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multixact.c
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1 /*-------------------------------------------------------------------------
2  *
3  * multixact.c
4  * PostgreSQL multi-transaction-log manager
5  *
6  * The pg_multixact manager is a pg_xact-like manager that stores an array of
7  * MultiXactMember for each MultiXactId. It is a fundamental part of the
8  * shared-row-lock implementation. Each MultiXactMember is comprised of a
9  * TransactionId and a set of flag bits. The name is a bit historical:
10  * originally, a MultiXactId consisted of more than one TransactionId (except
11  * in rare corner cases), hence "multi". Nowadays, however, it's perfectly
12  * legitimate to have MultiXactIds that only include a single Xid.
13  *
14  * The meaning of the flag bits is opaque to this module, but they are mostly
15  * used in heapam.c to identify lock modes that each of the member transactions
16  * is holding on any given tuple. This module just contains support to store
17  * and retrieve the arrays.
18  *
19  * We use two SLRU areas, one for storing the offsets at which the data
20  * starts for each MultiXactId in the other one. This trick allows us to
21  * store variable length arrays of TransactionIds. (We could alternatively
22  * use one area containing counts and TransactionIds, with valid MultiXactId
23  * values pointing at slots containing counts; but that way seems less robust
24  * since it would get completely confused if someone inquired about a bogus
25  * MultiXactId that pointed to an intermediate slot containing an XID.)
26  *
27  * XLOG interactions: this module generates a record whenever a new OFFSETs or
28  * MEMBERs page is initialized to zeroes, as well as an
29  * XLOG_MULTIXACT_CREATE_ID record whenever a new MultiXactId is defined.
30  * This module ignores the WAL rule "write xlog before data," because it
31  * suffices that actions recording a MultiXactId in a heap xmax do follow that
32  * rule. The only way for the MXID to be referenced from any data page is for
33  * heap_lock_tuple() or heap_update() to have put it there, and each generates
34  * an XLOG record that must follow ours. The normal LSN interlock between the
35  * data page and that XLOG record will ensure that our XLOG record reaches
36  * disk first. If the SLRU members/offsets data reaches disk sooner than the
37  * XLOG records, we do not care; after recovery, no xmax will refer to it. On
38  * the flip side, to ensure that all referenced entries _do_ reach disk, this
39  * module's XLOG records completely rebuild the data entered since the last
40  * checkpoint. We flush and sync all dirty OFFSETs and MEMBERs pages to disk
41  * before each checkpoint is considered complete.
42  *
43  * Like clog.c, and unlike subtrans.c, we have to preserve state across
44  * crashes and ensure that MXID and offset numbering increases monotonically
45  * across a crash. We do this in the same way as it's done for transaction
46  * IDs: the WAL record is guaranteed to contain evidence of every MXID we
47  * could need to worry about, and we just make sure that at the end of
48  * replay, the next-MXID and next-offset counters are at least as large as
49  * anything we saw during replay.
50  *
51  * We are able to remove segments no longer necessary by carefully tracking
52  * each table's used values: during vacuum, any multixact older than a certain
53  * value is removed; the cutoff value is stored in pg_class. The minimum value
54  * across all tables in each database is stored in pg_database, and the global
55  * minimum across all databases is part of pg_control and is kept in shared
56  * memory. Whenever that minimum is advanced, the SLRUs are truncated.
57  *
58  * When new multixactid values are to be created, care is taken that the
59  * counter does not fall within the wraparound horizon considering the global
60  * minimum value.
61  *
62  * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
63  * Portions Copyright (c) 1994, Regents of the University of California
64  *
65  * src/backend/access/transam/multixact.c
66  *
67  *-------------------------------------------------------------------------
68  */
69 #include "postgres.h"
70 
71 #include "access/multixact.h"
72 #include "access/slru.h"
73 #include "access/transam.h"
74 #include "access/twophase.h"
75 #include "access/twophase_rmgr.h"
76 #include "access/xact.h"
77 #include "access/xlog.h"
78 #include "access/xloginsert.h"
79 #include "catalog/pg_type.h"
80 #include "commands/dbcommands.h"
81 #include "funcapi.h"
82 #include "lib/ilist.h"
83 #include "miscadmin.h"
84 #include "pg_trace.h"
85 #include "postmaster/autovacuum.h"
86 #include "storage/lmgr.h"
87 #include "storage/pmsignal.h"
88 #include "storage/proc.h"
89 #include "storage/procarray.h"
90 #include "utils/builtins.h"
91 #include "utils/memutils.h"
92 #include "utils/snapmgr.h"
93 
94 
95 /*
96  * Defines for MultiXactOffset page sizes. A page is the same BLCKSZ as is
97  * used everywhere else in Postgres.
98  *
99  * Note: because MultiXactOffsets are 32 bits and wrap around at 0xFFFFFFFF,
100  * MultiXact page numbering also wraps around at
101  * 0xFFFFFFFF/MULTIXACT_OFFSETS_PER_PAGE, and segment numbering at
102  * 0xFFFFFFFF/MULTIXACT_OFFSETS_PER_PAGE/SLRU_PAGES_PER_SEGMENT. We need
103  * take no explicit notice of that fact in this module, except when comparing
104  * segment and page numbers in TruncateMultiXact (see
105  * MultiXactOffsetPagePrecedes).
106  */
107 
108 /* We need four bytes per offset */
109 #define MULTIXACT_OFFSETS_PER_PAGE (BLCKSZ / sizeof(MultiXactOffset))
110 
111 #define MultiXactIdToOffsetPage(xid) \
112  ((xid) / (MultiXactOffset) MULTIXACT_OFFSETS_PER_PAGE)
113 #define MultiXactIdToOffsetEntry(xid) \
114  ((xid) % (MultiXactOffset) MULTIXACT_OFFSETS_PER_PAGE)
115 #define MultiXactIdToOffsetSegment(xid) (MultiXactIdToOffsetPage(xid) / SLRU_PAGES_PER_SEGMENT)
116 
117 /*
118  * The situation for members is a bit more complex: we store one byte of
119  * additional flag bits for each TransactionId. To do this without getting
120  * into alignment issues, we store four bytes of flags, and then the
121  * corresponding 4 Xids. Each such 5-word (20-byte) set we call a "group", and
122  * are stored as a whole in pages. Thus, with 8kB BLCKSZ, we keep 409 groups
123  * per page. This wastes 12 bytes per page, but that's OK -- simplicity (and
124  * performance) trumps space efficiency here.
125  *
126  * Note that the "offset" macros work with byte offset, not array indexes, so
127  * arithmetic must be done using "char *" pointers.
128  */
129 /* We need eight bits per xact, so one xact fits in a byte */
130 #define MXACT_MEMBER_BITS_PER_XACT 8
131 #define MXACT_MEMBER_FLAGS_PER_BYTE 1
132 #define MXACT_MEMBER_XACT_BITMASK ((1 << MXACT_MEMBER_BITS_PER_XACT) - 1)
133 
134 /* how many full bytes of flags are there in a group? */
135 #define MULTIXACT_FLAGBYTES_PER_GROUP 4
136 #define MULTIXACT_MEMBERS_PER_MEMBERGROUP \
137  (MULTIXACT_FLAGBYTES_PER_GROUP * MXACT_MEMBER_FLAGS_PER_BYTE)
138 /* size in bytes of a complete group */
139 #define MULTIXACT_MEMBERGROUP_SIZE \
140  (sizeof(TransactionId) * MULTIXACT_MEMBERS_PER_MEMBERGROUP + MULTIXACT_FLAGBYTES_PER_GROUP)
141 #define MULTIXACT_MEMBERGROUPS_PER_PAGE (BLCKSZ / MULTIXACT_MEMBERGROUP_SIZE)
142 #define MULTIXACT_MEMBERS_PER_PAGE \
143  (MULTIXACT_MEMBERGROUPS_PER_PAGE * MULTIXACT_MEMBERS_PER_MEMBERGROUP)
144 
145 /*
146  * Because the number of items per page is not a divisor of the last item
147  * number (member 0xFFFFFFFF), the last segment does not use the maximum number
148  * of pages, and moreover the last used page therein does not use the same
149  * number of items as previous pages. (Another way to say it is that the
150  * 0xFFFFFFFF member is somewhere in the middle of the last page, so the page
151  * has some empty space after that item.)
152  *
153  * This constant is the number of members in the last page of the last segment.
154  */
155 #define MAX_MEMBERS_IN_LAST_MEMBERS_PAGE \
156  ((uint32) ((0xFFFFFFFF % MULTIXACT_MEMBERS_PER_PAGE) + 1))
157 
158 /* page in which a member is to be found */
159 #define MXOffsetToMemberPage(xid) ((xid) / (TransactionId) MULTIXACT_MEMBERS_PER_PAGE)
160 #define MXOffsetToMemberSegment(xid) (MXOffsetToMemberPage(xid) / SLRU_PAGES_PER_SEGMENT)
161 
162 /* Location (byte offset within page) of flag word for a given member */
163 #define MXOffsetToFlagsOffset(xid) \
164  ((((xid) / (TransactionId) MULTIXACT_MEMBERS_PER_MEMBERGROUP) % \
165  (TransactionId) MULTIXACT_MEMBERGROUPS_PER_PAGE) * \
166  (TransactionId) MULTIXACT_MEMBERGROUP_SIZE)
167 #define MXOffsetToFlagsBitShift(xid) \
168  (((xid) % (TransactionId) MULTIXACT_MEMBERS_PER_MEMBERGROUP) * \
169  MXACT_MEMBER_BITS_PER_XACT)
170 
171 /* Location (byte offset within page) of TransactionId of given member */
172 #define MXOffsetToMemberOffset(xid) \
173  (MXOffsetToFlagsOffset(xid) + MULTIXACT_FLAGBYTES_PER_GROUP + \
174  ((xid) % MULTIXACT_MEMBERS_PER_MEMBERGROUP) * sizeof(TransactionId))
175 
176 /* Multixact members wraparound thresholds. */
177 #define MULTIXACT_MEMBER_SAFE_THRESHOLD (MaxMultiXactOffset / 2)
178 #define MULTIXACT_MEMBER_DANGER_THRESHOLD \
179  (MaxMultiXactOffset - MaxMultiXactOffset / 4)
180 
181 #define PreviousMultiXactId(xid) \
182  ((xid) == FirstMultiXactId ? MaxMultiXactId : (xid) - 1)
183 
184 /*
185  * Links to shared-memory data structures for MultiXact control
186  */
189 
190 #define MultiXactOffsetCtl (&MultiXactOffsetCtlData)
191 #define MultiXactMemberCtl (&MultiXactMemberCtlData)
192 
193 /*
194  * MultiXact state shared across all backends. All this state is protected
195  * by MultiXactGenLock. (We also use MultiXactOffsetControlLock and
196  * MultiXactMemberControlLock to guard accesses to the two sets of SLRU
197  * buffers. For concurrency's sake, we avoid holding more than one of these
198  * locks at a time.)
199  */
200 typedef struct MultiXactStateData
201 {
202  /* next-to-be-assigned MultiXactId */
204 
205  /* next-to-be-assigned offset */
207 
208  /* Have we completed multixact startup? */
210 
211  /*
212  * Oldest multixact that is still potentially referenced by a relation.
213  * Anything older than this should not be consulted. These values are
214  * updated by vacuum.
215  */
218 
219  /*
220  * Oldest multixact offset that is potentially referenced by a multixact
221  * referenced by a relation. We don't always know this value, so there's
222  * a flag here to indicate whether or not we currently do.
223  */
226 
227  /* support for anti-wraparound measures */
232 
233  /* support for members anti-wraparound measures */
234  MultiXactOffset offsetStopLimit; /* known if oldestOffsetKnown */
235 
236  /*
237  * Per-backend data starts here. We have two arrays stored in the area
238  * immediately following the MultiXactStateData struct. Each is indexed by
239  * BackendId.
240  *
241  * In both arrays, there's a slot for all normal backends (1..MaxBackends)
242  * followed by a slot for max_prepared_xacts prepared transactions. Valid
243  * BackendIds start from 1; element zero of each array is never used.
244  *
245  * OldestMemberMXactId[k] is the oldest MultiXactId each backend's current
246  * transaction(s) could possibly be a member of, or InvalidMultiXactId
247  * when the backend has no live transaction that could possibly be a
248  * member of a MultiXact. Each backend sets its entry to the current
249  * nextMXact counter just before first acquiring a shared lock in a given
250  * transaction, and clears it at transaction end. (This works because only
251  * during or after acquiring a shared lock could an XID possibly become a
252  * member of a MultiXact, and that MultiXact would have to be created
253  * during or after the lock acquisition.)
254  *
255  * OldestVisibleMXactId[k] is the oldest MultiXactId each backend's
256  * current transaction(s) think is potentially live, or InvalidMultiXactId
257  * when not in a transaction or not in a transaction that's paid any
258  * attention to MultiXacts yet. This is computed when first needed in a
259  * given transaction, and cleared at transaction end. We can compute it
260  * as the minimum of the valid OldestMemberMXactId[] entries at the time
261  * we compute it (using nextMXact if none are valid). Each backend is
262  * required not to attempt to access any SLRU data for MultiXactIds older
263  * than its own OldestVisibleMXactId[] setting; this is necessary because
264  * the checkpointer could truncate away such data at any instant.
265  *
266  * The oldest valid value among all of the OldestMemberMXactId[] and
267  * OldestVisibleMXactId[] entries is considered by vacuum as the earliest
268  * possible value still having any live member transaction. Subtracting
269  * vacuum_multixact_freeze_min_age from that value we obtain the freezing
270  * point for multixacts for that table. Any value older than that is
271  * removed from tuple headers (or "frozen"; see FreezeMultiXactId. Note
272  * that multis that have member xids that are older than the cutoff point
273  * for xids must also be frozen, even if the multis themselves are newer
274  * than the multixid cutoff point). Whenever a full table vacuum happens,
275  * the freezing point so computed is used as the new pg_class.relminmxid
276  * value. The minimum of all those values in a database is stored as
277  * pg_database.datminmxid. In turn, the minimum of all of those values is
278  * stored in pg_control and used as truncation point for pg_multixact. At
279  * checkpoint or restartpoint, unneeded segments are removed.
280  */
281  MultiXactId perBackendXactIds[FLEXIBLE_ARRAY_MEMBER];
283 
284 /*
285  * Last element of OldestMemberMXactID and OldestVisibleMXactId arrays.
286  * Valid elements are (1..MaxOldestSlot); element 0 is never used.
287  */
288 #define MaxOldestSlot (MaxBackends + max_prepared_xacts)
289 
290 /* Pointers to the state data in shared memory */
294 
295 
296 /*
297  * Definitions for the backend-local MultiXactId cache.
298  *
299  * We use this cache to store known MultiXacts, so we don't need to go to
300  * SLRU areas every time.
301  *
302  * The cache lasts for the duration of a single transaction, the rationale
303  * for this being that most entries will contain our own TransactionId and
304  * so they will be uninteresting by the time our next transaction starts.
305  * (XXX not clear that this is correct --- other members of the MultiXact
306  * could hang around longer than we did. However, it's not clear what a
307  * better policy for flushing old cache entries would be.) FIXME actually
308  * this is plain wrong now that multixact's may contain update Xids.
309  *
310  * We allocate the cache entries in a memory context that is deleted at
311  * transaction end, so we don't need to do retail freeing of entries.
312  */
313 typedef struct mXactCacheEnt
314 {
316  int nmembers;
318  MultiXactMember members[FLEXIBLE_ARRAY_MEMBER];
319 } mXactCacheEnt;
320 
321 #define MAX_CACHE_ENTRIES 256
323 static int MXactCacheMembers = 0;
325 
326 #ifdef MULTIXACT_DEBUG
327 #define debug_elog2(a,b) elog(a,b)
328 #define debug_elog3(a,b,c) elog(a,b,c)
329 #define debug_elog4(a,b,c,d) elog(a,b,c,d)
330 #define debug_elog5(a,b,c,d,e) elog(a,b,c,d,e)
331 #define debug_elog6(a,b,c,d,e,f) elog(a,b,c,d,e,f)
332 #else
333 #define debug_elog2(a,b)
334 #define debug_elog3(a,b,c)
335 #define debug_elog4(a,b,c,d)
336 #define debug_elog5(a,b,c,d,e)
337 #define debug_elog6(a,b,c,d,e,f)
338 #endif
339 
340 /* internal MultiXactId management */
341 static void MultiXactIdSetOldestVisible(void);
342 static void RecordNewMultiXact(MultiXactId multi, MultiXactOffset offset,
343  int nmembers, MultiXactMember *members);
344 static MultiXactId GetNewMultiXactId(int nmembers, MultiXactOffset *offset);
345 
346 /* MultiXact cache management */
347 static int mxactMemberComparator(const void *arg1, const void *arg2);
348 static MultiXactId mXactCacheGetBySet(int nmembers, MultiXactMember *members);
349 static int mXactCacheGetById(MultiXactId multi, MultiXactMember **members);
350 static void mXactCachePut(MultiXactId multi, int nmembers,
351  MultiXactMember *members);
352 
354 
355 /* management of SLRU infrastructure */
356 static int ZeroMultiXactOffsetPage(int pageno, bool writeXlog);
357 static int ZeroMultiXactMemberPage(int pageno, bool writeXlog);
358 static bool MultiXactOffsetPagePrecedes(int page1, int page2);
359 static bool MultiXactMemberPagePrecedes(int page1, int page2);
360 static bool MultiXactOffsetPrecedes(MultiXactOffset offset1,
361  MultiXactOffset offset2);
362 static void ExtendMultiXactOffset(MultiXactId multi);
363 static void ExtendMultiXactMember(MultiXactOffset offset, int nmembers);
364 static bool MultiXactOffsetWouldWrap(MultiXactOffset boundary,
365  MultiXactOffset start, uint32 distance);
366 static bool SetOffsetVacuumLimit(bool is_startup);
368 static void WriteMZeroPageXlogRec(int pageno, uint8 info);
369 static void WriteMTruncateXlogRec(Oid oldestMultiDB,
370  MultiXactId startOff, MultiXactId endOff,
371  MultiXactOffset startMemb, MultiXactOffset endMemb);
372 
373 
374 /*
375  * MultiXactIdCreate
376  * Construct a MultiXactId representing two TransactionIds.
377  *
378  * The two XIDs must be different, or be requesting different statuses.
379  *
380  * NB - we don't worry about our local MultiXactId cache here, because that
381  * is handled by the lower-level routines.
382  */
385  TransactionId xid2, MultiXactStatus status2)
386 {
387  MultiXactId newMulti;
388  MultiXactMember members[2];
389 
392 
393  Assert(!TransactionIdEquals(xid1, xid2) || (status1 != status2));
394 
395  /* MultiXactIdSetOldestMember() must have been called already. */
397 
398  /*
399  * Note: unlike MultiXactIdExpand, we don't bother to check that both XIDs
400  * are still running. In typical usage, xid2 will be our own XID and the
401  * caller just did a check on xid1, so it'd be wasted effort.
402  */
403 
404  members[0].xid = xid1;
405  members[0].status = status1;
406  members[1].xid = xid2;
407  members[1].status = status2;
408 
409  newMulti = MultiXactIdCreateFromMembers(2, members);
410 
411  debug_elog3(DEBUG2, "Create: %s",
412  mxid_to_string(newMulti, 2, members));
413 
414  return newMulti;
415 }
416 
417 /*
418  * MultiXactIdExpand
419  * Add a TransactionId to a pre-existing MultiXactId.
420  *
421  * If the TransactionId is already a member of the passed MultiXactId with the
422  * same status, just return it as-is.
423  *
424  * Note that we do NOT actually modify the membership of a pre-existing
425  * MultiXactId; instead we create a new one. This is necessary to avoid
426  * a race condition against code trying to wait for one MultiXactId to finish;
427  * see notes in heapam.c.
428  *
429  * NB - we don't worry about our local MultiXactId cache here, because that
430  * is handled by the lower-level routines.
431  *
432  * Note: It is critical that MultiXactIds that come from an old cluster (i.e.
433  * one upgraded by pg_upgrade from a cluster older than this feature) are not
434  * passed in.
435  */
438 {
439  MultiXactId newMulti;
440  MultiXactMember *members;
441  MultiXactMember *newMembers;
442  int nmembers;
443  int i;
444  int j;
445 
448 
449  /* MultiXactIdSetOldestMember() must have been called already. */
451 
452  debug_elog5(DEBUG2, "Expand: received multi %u, xid %u status %s",
453  multi, xid, mxstatus_to_string(status));
454 
455  /*
456  * Note: we don't allow for old multis here. The reason is that the only
457  * caller of this function does a check that the multixact is no longer
458  * running.
459  */
460  nmembers = GetMultiXactIdMembers(multi, &members, false, false);
461 
462  if (nmembers < 0)
463  {
464  MultiXactMember member;
465 
466  /*
467  * The MultiXactId is obsolete. This can only happen if all the
468  * MultiXactId members stop running between the caller checking and
469  * passing it to us. It would be better to return that fact to the
470  * caller, but it would complicate the API and it's unlikely to happen
471  * too often, so just deal with it by creating a singleton MultiXact.
472  */
473  member.xid = xid;
474  member.status = status;
475  newMulti = MultiXactIdCreateFromMembers(1, &member);
476 
477  debug_elog4(DEBUG2, "Expand: %u has no members, create singleton %u",
478  multi, newMulti);
479  return newMulti;
480  }
481 
482  /*
483  * If the TransactionId is already a member of the MultiXactId with the
484  * same status, just return the existing MultiXactId.
485  */
486  for (i = 0; i < nmembers; i++)
487  {
488  if (TransactionIdEquals(members[i].xid, xid) &&
489  (members[i].status == status))
490  {
491  debug_elog4(DEBUG2, "Expand: %u is already a member of %u",
492  xid, multi);
493  pfree(members);
494  return multi;
495  }
496  }
497 
498  /*
499  * Determine which of the members of the MultiXactId are still of
500  * interest. This is any running transaction, and also any transaction
501  * that grabbed something stronger than just a lock and was committed. (An
502  * update that aborted is of no interest here; and having more than one
503  * update Xid in a multixact would cause errors elsewhere.)
504  *
505  * Removing dead members is not just an optimization: freezing of tuples
506  * whose Xmax are multis depends on this behavior.
507  *
508  * Note we have the same race condition here as above: j could be 0 at the
509  * end of the loop.
510  */
511  newMembers = (MultiXactMember *)
512  palloc(sizeof(MultiXactMember) * (nmembers + 1));
513 
514  for (i = 0, j = 0; i < nmembers; i++)
515  {
516  if (TransactionIdIsInProgress(members[i].xid) ||
517  (ISUPDATE_from_mxstatus(members[i].status) &&
518  TransactionIdDidCommit(members[i].xid)))
519  {
520  newMembers[j].xid = members[i].xid;
521  newMembers[j++].status = members[i].status;
522  }
523  }
524 
525  newMembers[j].xid = xid;
526  newMembers[j++].status = status;
527  newMulti = MultiXactIdCreateFromMembers(j, newMembers);
528 
529  pfree(members);
530  pfree(newMembers);
531 
532  debug_elog3(DEBUG2, "Expand: returning new multi %u", newMulti);
533 
534  return newMulti;
535 }
536 
537 /*
538  * MultiXactIdIsRunning
539  * Returns whether a MultiXactId is "running".
540  *
541  * We return true if at least one member of the given MultiXactId is still
542  * running. Note that a "false" result is certain not to change,
543  * because it is not legal to add members to an existing MultiXactId.
544  *
545  * Caller is expected to have verified that the multixact does not come from
546  * a pg_upgraded share-locked tuple.
547  */
548 bool
549 MultiXactIdIsRunning(MultiXactId multi, bool isLockOnly)
550 {
551  MultiXactMember *members;
552  int nmembers;
553  int i;
554 
555  debug_elog3(DEBUG2, "IsRunning %u?", multi);
556 
557  /*
558  * "false" here means we assume our callers have checked that the given
559  * multi cannot possibly come from a pg_upgraded database.
560  */
561  nmembers = GetMultiXactIdMembers(multi, &members, false, isLockOnly);
562 
563  if (nmembers <= 0)
564  {
565  debug_elog2(DEBUG2, "IsRunning: no members");
566  return false;
567  }
568 
569  /*
570  * Checking for myself is cheap compared to looking in shared memory;
571  * return true if any live subtransaction of the current top-level
572  * transaction is a member.
573  *
574  * This is not needed for correctness, it's just a fast path.
575  */
576  for (i = 0; i < nmembers; i++)
577  {
578  if (TransactionIdIsCurrentTransactionId(members[i].xid))
579  {
580  debug_elog3(DEBUG2, "IsRunning: I (%d) am running!", i);
581  pfree(members);
582  return true;
583  }
584  }
585 
586  /*
587  * This could be made faster by having another entry point in procarray.c,
588  * walking the PGPROC array only once for all the members. But in most
589  * cases nmembers should be small enough that it doesn't much matter.
590  */
591  for (i = 0; i < nmembers; i++)
592  {
593  if (TransactionIdIsInProgress(members[i].xid))
594  {
595  debug_elog4(DEBUG2, "IsRunning: member %d (%u) is running",
596  i, members[i].xid);
597  pfree(members);
598  return true;
599  }
600  }
601 
602  pfree(members);
603 
604  debug_elog3(DEBUG2, "IsRunning: %u is not running", multi);
605 
606  return false;
607 }
608 
609 /*
610  * MultiXactIdSetOldestMember
611  * Save the oldest MultiXactId this transaction could be a member of.
612  *
613  * We set the OldestMemberMXactId for a given transaction the first time it's
614  * going to do some operation that might require a MultiXactId (tuple lock,
615  * update or delete). We need to do this even if we end up using a
616  * TransactionId instead of a MultiXactId, because there is a chance that
617  * another transaction would add our XID to a MultiXactId.
618  *
619  * The value to set is the next-to-be-assigned MultiXactId, so this is meant to
620  * be called just before doing any such possibly-MultiXactId-able operation.
621  */
622 void
624 {
626  {
627  MultiXactId nextMXact;
628 
629  /*
630  * You might think we don't need to acquire a lock here, since
631  * fetching and storing of TransactionIds is probably atomic, but in
632  * fact we do: suppose we pick up nextMXact and then lose the CPU for
633  * a long time. Someone else could advance nextMXact, and then
634  * another someone else could compute an OldestVisibleMXactId that
635  * would be after the value we are going to store when we get control
636  * back. Which would be wrong.
637  *
638  * Note that a shared lock is sufficient, because it's enough to stop
639  * someone from advancing nextMXact; and nobody else could be trying
640  * to write to our OldestMember entry, only reading (and we assume
641  * storing it is atomic.)
642  */
643  LWLockAcquire(MultiXactGenLock, LW_SHARED);
644 
645  /*
646  * We have to beware of the possibility that nextMXact is in the
647  * wrapped-around state. We don't fix the counter itself here, but we
648  * must be sure to store a valid value in our array entry.
649  */
650  nextMXact = MultiXactState->nextMXact;
651  if (nextMXact < FirstMultiXactId)
652  nextMXact = FirstMultiXactId;
653 
654  OldestMemberMXactId[MyBackendId] = nextMXact;
655 
656  LWLockRelease(MultiXactGenLock);
657 
658  debug_elog4(DEBUG2, "MultiXact: setting OldestMember[%d] = %u",
659  MyBackendId, nextMXact);
660  }
661 }
662 
663 /*
664  * MultiXactIdSetOldestVisible
665  * Save the oldest MultiXactId this transaction considers possibly live.
666  *
667  * We set the OldestVisibleMXactId for a given transaction the first time
668  * it's going to inspect any MultiXactId. Once we have set this, we are
669  * guaranteed that the checkpointer won't truncate off SLRU data for
670  * MultiXactIds at or after our OldestVisibleMXactId.
671  *
672  * The value to set is the oldest of nextMXact and all the valid per-backend
673  * OldestMemberMXactId[] entries. Because of the locking we do, we can be
674  * certain that no subsequent call to MultiXactIdSetOldestMember can set
675  * an OldestMemberMXactId[] entry older than what we compute here. Therefore
676  * there is no live transaction, now or later, that can be a member of any
677  * MultiXactId older than the OldestVisibleMXactId we compute here.
678  */
679 static void
681 {
683  {
684  MultiXactId oldestMXact;
685  int i;
686 
687  LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
688 
689  /*
690  * We have to beware of the possibility that nextMXact is in the
691  * wrapped-around state. We don't fix the counter itself here, but we
692  * must be sure to store a valid value in our array entry.
693  */
694  oldestMXact = MultiXactState->nextMXact;
695  if (oldestMXact < FirstMultiXactId)
696  oldestMXact = FirstMultiXactId;
697 
698  for (i = 1; i <= MaxOldestSlot; i++)
699  {
700  MultiXactId thisoldest = OldestMemberMXactId[i];
701 
702  if (MultiXactIdIsValid(thisoldest) &&
703  MultiXactIdPrecedes(thisoldest, oldestMXact))
704  oldestMXact = thisoldest;
705  }
706 
707  OldestVisibleMXactId[MyBackendId] = oldestMXact;
708 
709  LWLockRelease(MultiXactGenLock);
710 
711  debug_elog4(DEBUG2, "MultiXact: setting OldestVisible[%d] = %u",
712  MyBackendId, oldestMXact);
713  }
714 }
715 
716 /*
717  * ReadNextMultiXactId
718  * Return the next MultiXactId to be assigned, but don't allocate it
719  */
722 {
723  MultiXactId mxid;
724 
725  /* XXX we could presumably do this without a lock. */
726  LWLockAcquire(MultiXactGenLock, LW_SHARED);
727  mxid = MultiXactState->nextMXact;
728  LWLockRelease(MultiXactGenLock);
729 
730  if (mxid < FirstMultiXactId)
731  mxid = FirstMultiXactId;
732 
733  return mxid;
734 }
735 
736 /*
737  * MultiXactIdCreateFromMembers
738  * Make a new MultiXactId from the specified set of members
739  *
740  * Make XLOG, SLRU and cache entries for a new MultiXactId, recording the
741  * given TransactionIds as members. Returns the newly created MultiXactId.
742  *
743  * NB: the passed members[] array will be sorted in-place.
744  */
747 {
748  MultiXactId multi;
749  MultiXactOffset offset;
750  xl_multixact_create xlrec;
751 
752  debug_elog3(DEBUG2, "Create: %s",
753  mxid_to_string(InvalidMultiXactId, nmembers, members));
754 
755  /*
756  * See if the same set of members already exists in our cache; if so, just
757  * re-use that MultiXactId. (Note: it might seem that looking in our
758  * cache is insufficient, and we ought to search disk to see if a
759  * duplicate definition already exists. But since we only ever create
760  * MultiXacts containing our own XID, in most cases any such MultiXacts
761  * were in fact created by us, and so will be in our cache. There are
762  * corner cases where someone else added us to a MultiXact without our
763  * knowledge, but it's not worth checking for.)
764  */
765  multi = mXactCacheGetBySet(nmembers, members);
766  if (MultiXactIdIsValid(multi))
767  {
768  debug_elog2(DEBUG2, "Create: in cache!");
769  return multi;
770  }
771 
772  /* Verify that there is a single update Xid among the given members. */
773  {
774  int i;
775  bool has_update = false;
776 
777  for (i = 0; i < nmembers; i++)
778  {
779  if (ISUPDATE_from_mxstatus(members[i].status))
780  {
781  if (has_update)
782  elog(ERROR, "new multixact has more than one updating member");
783  has_update = true;
784  }
785  }
786  }
787 
788  /*
789  * Assign the MXID and offsets range to use, and make sure there is space
790  * in the OFFSETs and MEMBERs files. NB: this routine does
791  * START_CRIT_SECTION().
792  *
793  * Note: unlike MultiXactIdCreate and MultiXactIdExpand, we do not check
794  * that we've called MultiXactIdSetOldestMember here. This is because
795  * this routine is used in some places to create new MultiXactIds of which
796  * the current backend is not a member, notably during freezing of multis
797  * in vacuum. During vacuum, in particular, it would be unacceptable to
798  * keep OldestMulti set, in case it runs for long.
799  */
800  multi = GetNewMultiXactId(nmembers, &offset);
801 
802  /* Make an XLOG entry describing the new MXID. */
803  xlrec.mid = multi;
804  xlrec.moff = offset;
805  xlrec.nmembers = nmembers;
806 
807  /*
808  * XXX Note: there's a lot of padding space in MultiXactMember. We could
809  * find a more compact representation of this Xlog record -- perhaps all
810  * the status flags in one XLogRecData, then all the xids in another one?
811  * Not clear that it's worth the trouble though.
812  */
813  XLogBeginInsert();
814  XLogRegisterData((char *) (&xlrec), SizeOfMultiXactCreate);
815  XLogRegisterData((char *) members, nmembers * sizeof(MultiXactMember));
816 
817  (void) XLogInsert(RM_MULTIXACT_ID, XLOG_MULTIXACT_CREATE_ID);
818 
819  /* Now enter the information into the OFFSETs and MEMBERs logs */
820  RecordNewMultiXact(multi, offset, nmembers, members);
821 
822  /* Done with critical section */
824 
825  /* Store the new MultiXactId in the local cache, too */
826  mXactCachePut(multi, nmembers, members);
827 
828  debug_elog2(DEBUG2, "Create: all done");
829 
830  return multi;
831 }
832 
833 /*
834  * RecordNewMultiXact
835  * Write info about a new multixact into the offsets and members files
836  *
837  * This is broken out of MultiXactIdCreateFromMembers so that xlog replay can
838  * use it.
839  */
840 static void
842  int nmembers, MultiXactMember *members)
843 {
844  int pageno;
845  int prev_pageno;
846  int entryno;
847  int slotno;
848  MultiXactOffset *offptr;
849  int i;
850 
851  LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
852 
853  pageno = MultiXactIdToOffsetPage(multi);
854  entryno = MultiXactIdToOffsetEntry(multi);
855 
856  /*
857  * Note: we pass the MultiXactId to SimpleLruReadPage as the "transaction"
858  * to complain about if there's any I/O error. This is kinda bogus, but
859  * since the errors will always give the full pathname, it should be clear
860  * enough that a MultiXactId is really involved. Perhaps someday we'll
861  * take the trouble to generalize the slru.c error reporting code.
862  */
863  slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, multi);
864  offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
865  offptr += entryno;
866 
867  *offptr = offset;
868 
869  MultiXactOffsetCtl->shared->page_dirty[slotno] = true;
870 
871  /* Exchange our lock */
872  LWLockRelease(MultiXactOffsetControlLock);
873 
874  LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
875 
876  prev_pageno = -1;
877 
878  for (i = 0; i < nmembers; i++, offset++)
879  {
880  TransactionId *memberptr;
881  uint32 *flagsptr;
882  uint32 flagsval;
883  int bshift;
884  int flagsoff;
885  int memberoff;
886 
887  Assert(members[i].status <= MultiXactStatusUpdate);
888 
889  pageno = MXOffsetToMemberPage(offset);
890  memberoff = MXOffsetToMemberOffset(offset);
891  flagsoff = MXOffsetToFlagsOffset(offset);
892  bshift = MXOffsetToFlagsBitShift(offset);
893 
894  if (pageno != prev_pageno)
895  {
896  slotno = SimpleLruReadPage(MultiXactMemberCtl, pageno, true, multi);
897  prev_pageno = pageno;
898  }
899 
900  memberptr = (TransactionId *)
901  (MultiXactMemberCtl->shared->page_buffer[slotno] + memberoff);
902 
903  *memberptr = members[i].xid;
904 
905  flagsptr = (uint32 *)
906  (MultiXactMemberCtl->shared->page_buffer[slotno] + flagsoff);
907 
908  flagsval = *flagsptr;
909  flagsval &= ~(((1 << MXACT_MEMBER_BITS_PER_XACT) - 1) << bshift);
910  flagsval |= (members[i].status << bshift);
911  *flagsptr = flagsval;
912 
913  MultiXactMemberCtl->shared->page_dirty[slotno] = true;
914  }
915 
916  LWLockRelease(MultiXactMemberControlLock);
917 }
918 
919 /*
920  * GetNewMultiXactId
921  * Get the next MultiXactId.
922  *
923  * Also, reserve the needed amount of space in the "members" area. The
924  * starting offset of the reserved space is returned in *offset.
925  *
926  * This may generate XLOG records for expansion of the offsets and/or members
927  * files. Unfortunately, we have to do that while holding MultiXactGenLock
928  * to avoid race conditions --- the XLOG record for zeroing a page must appear
929  * before any backend can possibly try to store data in that page!
930  *
931  * We start a critical section before advancing the shared counters. The
932  * caller must end the critical section after writing SLRU data.
933  */
934 static MultiXactId
935 GetNewMultiXactId(int nmembers, MultiXactOffset *offset)
936 {
938  MultiXactOffset nextOffset;
939 
940  debug_elog3(DEBUG2, "GetNew: for %d xids", nmembers);
941 
942  /* safety check, we should never get this far in a HS slave */
943  if (RecoveryInProgress())
944  elog(ERROR, "cannot assign MultiXactIds during recovery");
945 
946  LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
947 
948  /* Handle wraparound of the nextMXact counter */
949  if (MultiXactState->nextMXact < FirstMultiXactId)
950  MultiXactState->nextMXact = FirstMultiXactId;
951 
952  /* Assign the MXID */
953  result = MultiXactState->nextMXact;
954 
955  /*----------
956  * Check to see if it's safe to assign another MultiXactId. This protects
957  * against catastrophic data loss due to multixact wraparound. The basic
958  * rules are:
959  *
960  * If we're past multiVacLimit or the safe threshold for member storage
961  * space, or we don't know what the safe threshold for member storage is,
962  * start trying to force autovacuum cycles.
963  * If we're past multiWarnLimit, start issuing warnings.
964  * If we're past multiStopLimit, refuse to create new MultiXactIds.
965  *
966  * Note these are pretty much the same protections in GetNewTransactionId.
967  *----------
968  */
969  if (!MultiXactIdPrecedes(result, MultiXactState->multiVacLimit))
970  {
971  /*
972  * For safety's sake, we release MultiXactGenLock while sending
973  * signals, warnings, etc. This is not so much because we care about
974  * preserving concurrency in this situation, as to avoid any
975  * possibility of deadlock while doing get_database_name(). First,
976  * copy all the shared values we'll need in this path.
977  */
978  MultiXactId multiWarnLimit = MultiXactState->multiWarnLimit;
979  MultiXactId multiStopLimit = MultiXactState->multiStopLimit;
980  MultiXactId multiWrapLimit = MultiXactState->multiWrapLimit;
981  Oid oldest_datoid = MultiXactState->oldestMultiXactDB;
982 
983  LWLockRelease(MultiXactGenLock);
984 
985  if (IsUnderPostmaster &&
986  !MultiXactIdPrecedes(result, multiStopLimit))
987  {
988  char *oldest_datname = get_database_name(oldest_datoid);
989 
990  /*
991  * Immediately kick autovacuum into action as we're already in
992  * ERROR territory.
993  */
995 
996  /* complain even if that DB has disappeared */
997  if (oldest_datname)
998  ereport(ERROR,
999  (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
1000  errmsg("database is not accepting commands that generate new MultiXactIds to avoid wraparound data loss in database \"%s\"",
1001  oldest_datname),
1002  errhint("Execute a database-wide VACUUM in that database.\n"
1003  "You might also need to commit or roll back old prepared transactions.")));
1004  else
1005  ereport(ERROR,
1006  (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
1007  errmsg("database is not accepting commands that generate new MultiXactIds to avoid wraparound data loss in database with OID %u",
1008  oldest_datoid),
1009  errhint("Execute a database-wide VACUUM in that database.\n"
1010  "You might also need to commit or roll back old prepared transactions.")));
1011  }
1012 
1013  /*
1014  * To avoid swamping the postmaster with signals, we issue the autovac
1015  * request only once per 64K multis generated. This still gives
1016  * plenty of chances before we get into real trouble.
1017  */
1018  if (IsUnderPostmaster && (result % 65536) == 0)
1020 
1021  if (!MultiXactIdPrecedes(result, multiWarnLimit))
1022  {
1023  char *oldest_datname = get_database_name(oldest_datoid);
1024 
1025  /* complain even if that DB has disappeared */
1026  if (oldest_datname)
1027  ereport(WARNING,
1028  (errmsg_plural("database \"%s\" must be vacuumed before %u more MultiXactId is used",
1029  "database \"%s\" must be vacuumed before %u more MultiXactIds are used",
1030  multiWrapLimit - result,
1031  oldest_datname,
1032  multiWrapLimit - result),
1033  errhint("Execute a database-wide VACUUM in that database.\n"
1034  "You might also need to commit or roll back old prepared transactions.")));
1035  else
1036  ereport(WARNING,
1037  (errmsg_plural("database with OID %u must be vacuumed before %u more MultiXactId is used",
1038  "database with OID %u must be vacuumed before %u more MultiXactIds are used",
1039  multiWrapLimit - result,
1040  oldest_datoid,
1041  multiWrapLimit - result),
1042  errhint("Execute a database-wide VACUUM in that database.\n"
1043  "You might also need to commit or roll back old prepared transactions.")));
1044  }
1045 
1046  /* Re-acquire lock and start over */
1047  LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
1048  result = MultiXactState->nextMXact;
1049  if (result < FirstMultiXactId)
1050  result = FirstMultiXactId;
1051  }
1052 
1053  /* Make sure there is room for the MXID in the file. */
1054  ExtendMultiXactOffset(result);
1055 
1056  /*
1057  * Reserve the members space, similarly to above. Also, be careful not to
1058  * return zero as the starting offset for any multixact. See
1059  * GetMultiXactIdMembers() for motivation.
1060  */
1061  nextOffset = MultiXactState->nextOffset;
1062  if (nextOffset == 0)
1063  {
1064  *offset = 1;
1065  nmembers++; /* allocate member slot 0 too */
1066  }
1067  else
1068  *offset = nextOffset;
1069 
1070  /*----------
1071  * Protect against overrun of the members space as well, with the
1072  * following rules:
1073  *
1074  * If we're past offsetStopLimit, refuse to generate more multis.
1075  * If we're close to offsetStopLimit, emit a warning.
1076  *
1077  * Arbitrarily, we start emitting warnings when we're 20 segments or less
1078  * from offsetStopLimit.
1079  *
1080  * Note we haven't updated the shared state yet, so if we fail at this
1081  * point, the multixact ID we grabbed can still be used by the next guy.
1082  *
1083  * Note that there is no point in forcing autovacuum runs here: the
1084  * multixact freeze settings would have to be reduced for that to have any
1085  * effect.
1086  *----------
1087  */
1088 #define OFFSET_WARN_SEGMENTS 20
1089  if (MultiXactState->oldestOffsetKnown &&
1090  MultiXactOffsetWouldWrap(MultiXactState->offsetStopLimit, nextOffset,
1091  nmembers))
1092  {
1093  /* see comment in the corresponding offsets wraparound case */
1095 
1096  ereport(ERROR,
1097  (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
1098  errmsg("multixact \"members\" limit exceeded"),
1099  errdetail_plural("This command would create a multixact with %u members, but the remaining space is only enough for %u member.",
1100  "This command would create a multixact with %u members, but the remaining space is only enough for %u members.",
1101  MultiXactState->offsetStopLimit - nextOffset - 1,
1102  nmembers,
1103  MultiXactState->offsetStopLimit - nextOffset - 1),
1104  errhint("Execute a database-wide VACUUM in database with OID %u with reduced vacuum_multixact_freeze_min_age and vacuum_multixact_freeze_table_age settings.",
1105  MultiXactState->oldestMultiXactDB)));
1106  }
1107 
1108  /*
1109  * Check whether we should kick autovacuum into action, to prevent members
1110  * wraparound. NB we use a much larger window to trigger autovacuum than
1111  * just the warning limit. The warning is just a measure of last resort -
1112  * this is in line with GetNewTransactionId's behaviour.
1113  */
1114  if (!MultiXactState->oldestOffsetKnown ||
1115  (MultiXactState->nextOffset - MultiXactState->oldestOffset
1117  {
1118  /*
1119  * To avoid swamping the postmaster with signals, we issue the autovac
1120  * request only when crossing a segment boundary. With default
1121  * compilation settings that's roughly after 50k members. This still
1122  * gives plenty of chances before we get into real trouble.
1123  */
1124  if ((MXOffsetToMemberPage(nextOffset) / SLRU_PAGES_PER_SEGMENT) !=
1125  (MXOffsetToMemberPage(nextOffset + nmembers) / SLRU_PAGES_PER_SEGMENT))
1127  }
1128 
1129  if (MultiXactState->oldestOffsetKnown &&
1130  MultiXactOffsetWouldWrap(MultiXactState->offsetStopLimit,
1131  nextOffset,
1133  ereport(WARNING,
1134  (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
1135  errmsg_plural("database with OID %u must be vacuumed before %d more multixact member is used",
1136  "database with OID %u must be vacuumed before %d more multixact members are used",
1137  MultiXactState->offsetStopLimit - nextOffset + nmembers,
1138  MultiXactState->oldestMultiXactDB,
1139  MultiXactState->offsetStopLimit - nextOffset + nmembers),
1140  errhint("Execute a database-wide VACUUM in that database with reduced vacuum_multixact_freeze_min_age and vacuum_multixact_freeze_table_age settings.")));
1141 
1142  ExtendMultiXactMember(nextOffset, nmembers);
1143 
1144  /*
1145  * Critical section from here until caller has written the data into the
1146  * just-reserved SLRU space; we don't want to error out with a partly
1147  * written MultiXact structure. (In particular, failing to write our
1148  * start offset after advancing nextMXact would effectively corrupt the
1149  * previous MultiXact.)
1150  */
1152 
1153  /*
1154  * Advance counters. As in GetNewTransactionId(), this must not happen
1155  * until after file extension has succeeded!
1156  *
1157  * We don't care about MultiXactId wraparound here; it will be handled by
1158  * the next iteration. But note that nextMXact may be InvalidMultiXactId
1159  * or the first value on a segment-beginning page after this routine
1160  * exits, so anyone else looking at the variable must be prepared to deal
1161  * with either case. Similarly, nextOffset may be zero, but we won't use
1162  * that as the actual start offset of the next multixact.
1163  */
1164  (MultiXactState->nextMXact)++;
1165 
1166  MultiXactState->nextOffset += nmembers;
1167 
1168  LWLockRelease(MultiXactGenLock);
1169 
1170  debug_elog4(DEBUG2, "GetNew: returning %u offset %u", result, *offset);
1171  return result;
1172 }
1173 
1174 /*
1175  * GetMultiXactIdMembers
1176  * Return the set of MultiXactMembers that make up a MultiXactId
1177  *
1178  * Return value is the number of members found, or -1 if there are none,
1179  * and *members is set to a newly palloc'ed array of members. It's the
1180  * caller's responsibility to free it when done with it.
1181  *
1182  * from_pgupgrade must be passed as true if and only if only the multixact
1183  * corresponds to a value from a tuple that was locked in a 9.2-or-older
1184  * installation and later pg_upgrade'd (that is, the infomask is
1185  * HEAP_LOCKED_UPGRADED). In this case, we know for certain that no members
1186  * can still be running, so we return -1 just like for an empty multixact
1187  * without any further checking. It would be wrong to try to resolve such a
1188  * multixact: either the multixact is within the current valid multixact
1189  * range, in which case the returned result would be bogus, or outside that
1190  * range, in which case an error would be raised.
1191  *
1192  * In all other cases, the passed multixact must be within the known valid
1193  * range, that is, greater to or equal than oldestMultiXactId, and less than
1194  * nextMXact. Otherwise, an error is raised.
1195  *
1196  * onlyLock must be set to true if caller is certain that the given multi
1197  * is used only to lock tuples; can be false without loss of correctness,
1198  * but passing a true means we can return quickly without checking for
1199  * old updates.
1200  */
1201 int
1203  bool from_pgupgrade, bool onlyLock)
1204 {
1205  int pageno;
1206  int prev_pageno;
1207  int entryno;
1208  int slotno;
1209  MultiXactOffset *offptr;
1210  MultiXactOffset offset;
1211  int length;
1212  int truelength;
1213  int i;
1214  MultiXactId oldestMXact;
1215  MultiXactId nextMXact;
1216  MultiXactId tmpMXact;
1217  MultiXactOffset nextOffset;
1218  MultiXactMember *ptr;
1219 
1220  debug_elog3(DEBUG2, "GetMembers: asked for %u", multi);
1221 
1222  if (!MultiXactIdIsValid(multi) || from_pgupgrade)
1223  return -1;
1224 
1225  /* See if the MultiXactId is in the local cache */
1226  length = mXactCacheGetById(multi, members);
1227  if (length >= 0)
1228  {
1229  debug_elog3(DEBUG2, "GetMembers: found %s in the cache",
1230  mxid_to_string(multi, length, *members));
1231  return length;
1232  }
1233 
1234  /* Set our OldestVisibleMXactId[] entry if we didn't already */
1236 
1237  /*
1238  * If we know the multi is used only for locking and not for updates, then
1239  * we can skip checking if the value is older than our oldest visible
1240  * multi. It cannot possibly still be running.
1241  */
1242  if (onlyLock &&
1244  {
1245  debug_elog2(DEBUG2, "GetMembers: a locker-only multi is too old");
1246  *members = NULL;
1247  return -1;
1248  }
1249 
1250  /*
1251  * We check known limits on MultiXact before resorting to the SLRU area.
1252  *
1253  * An ID older than MultiXactState->oldestMultiXactId cannot possibly be
1254  * useful; it has already been removed, or will be removed shortly, by
1255  * truncation. If one is passed, an error is raised.
1256  *
1257  * Also, an ID >= nextMXact shouldn't ever be seen here; if it is seen, it
1258  * implies undetected ID wraparound has occurred. This raises a hard
1259  * error.
1260  *
1261  * Shared lock is enough here since we aren't modifying any global state.
1262  * Acquire it just long enough to grab the current counter values. We may
1263  * need both nextMXact and nextOffset; see below.
1264  */
1265  LWLockAcquire(MultiXactGenLock, LW_SHARED);
1266 
1267  oldestMXact = MultiXactState->oldestMultiXactId;
1268  nextMXact = MultiXactState->nextMXact;
1269  nextOffset = MultiXactState->nextOffset;
1270 
1271  LWLockRelease(MultiXactGenLock);
1272 
1273  if (MultiXactIdPrecedes(multi, oldestMXact))
1274  {
1275  ereport(ERROR,
1276  (errcode(ERRCODE_INTERNAL_ERROR),
1277  errmsg("MultiXactId %u does no longer exist -- apparent wraparound",
1278  multi)));
1279  return -1;
1280  }
1281 
1282  if (!MultiXactIdPrecedes(multi, nextMXact))
1283  ereport(ERROR,
1284  (errcode(ERRCODE_INTERNAL_ERROR),
1285  errmsg("MultiXactId %u has not been created yet -- apparent wraparound",
1286  multi)));
1287 
1288  /*
1289  * Find out the offset at which we need to start reading MultiXactMembers
1290  * and the number of members in the multixact. We determine the latter as
1291  * the difference between this multixact's starting offset and the next
1292  * one's. However, there are some corner cases to worry about:
1293  *
1294  * 1. This multixact may be the latest one created, in which case there is
1295  * no next one to look at. In this case the nextOffset value we just
1296  * saved is the correct endpoint.
1297  *
1298  * 2. The next multixact may still be in process of being filled in: that
1299  * is, another process may have done GetNewMultiXactId but not yet written
1300  * the offset entry for that ID. In that scenario, it is guaranteed that
1301  * the offset entry for that multixact exists (because GetNewMultiXactId
1302  * won't release MultiXactGenLock until it does) but contains zero
1303  * (because we are careful to pre-zero offset pages). Because
1304  * GetNewMultiXactId will never return zero as the starting offset for a
1305  * multixact, when we read zero as the next multixact's offset, we know we
1306  * have this case. We sleep for a bit and try again.
1307  *
1308  * 3. Because GetNewMultiXactId increments offset zero to offset one to
1309  * handle case #2, there is an ambiguity near the point of offset
1310  * wraparound. If we see next multixact's offset is one, is that our
1311  * multixact's actual endpoint, or did it end at zero with a subsequent
1312  * increment? We handle this using the knowledge that if the zero'th
1313  * member slot wasn't filled, it'll contain zero, and zero isn't a valid
1314  * transaction ID so it can't be a multixact member. Therefore, if we
1315  * read a zero from the members array, just ignore it.
1316  *
1317  * This is all pretty messy, but the mess occurs only in infrequent corner
1318  * cases, so it seems better than holding the MultiXactGenLock for a long
1319  * time on every multixact creation.
1320  */
1321 retry:
1322  LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
1323 
1324  pageno = MultiXactIdToOffsetPage(multi);
1325  entryno = MultiXactIdToOffsetEntry(multi);
1326 
1327  slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, multi);
1328  offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
1329  offptr += entryno;
1330  offset = *offptr;
1331 
1332  Assert(offset != 0);
1333 
1334  /*
1335  * Use the same increment rule as GetNewMultiXactId(), that is, don't
1336  * handle wraparound explicitly until needed.
1337  */
1338  tmpMXact = multi + 1;
1339 
1340  if (nextMXact == tmpMXact)
1341  {
1342  /* Corner case 1: there is no next multixact */
1343  length = nextOffset - offset;
1344  }
1345  else
1346  {
1347  MultiXactOffset nextMXOffset;
1348 
1349  /* handle wraparound if needed */
1350  if (tmpMXact < FirstMultiXactId)
1351  tmpMXact = FirstMultiXactId;
1352 
1353  prev_pageno = pageno;
1354 
1355  pageno = MultiXactIdToOffsetPage(tmpMXact);
1356  entryno = MultiXactIdToOffsetEntry(tmpMXact);
1357 
1358  if (pageno != prev_pageno)
1359  slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, tmpMXact);
1360 
1361  offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
1362  offptr += entryno;
1363  nextMXOffset = *offptr;
1364 
1365  if (nextMXOffset == 0)
1366  {
1367  /* Corner case 2: next multixact is still being filled in */
1368  LWLockRelease(MultiXactOffsetControlLock);
1370  pg_usleep(1000L);
1371  goto retry;
1372  }
1373 
1374  length = nextMXOffset - offset;
1375  }
1376 
1377  LWLockRelease(MultiXactOffsetControlLock);
1378 
1379  ptr = (MultiXactMember *) palloc(length * sizeof(MultiXactMember));
1380  *members = ptr;
1381 
1382  /* Now get the members themselves. */
1383  LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
1384 
1385  truelength = 0;
1386  prev_pageno = -1;
1387  for (i = 0; i < length; i++, offset++)
1388  {
1389  TransactionId *xactptr;
1390  uint32 *flagsptr;
1391  int flagsoff;
1392  int bshift;
1393  int memberoff;
1394 
1395  pageno = MXOffsetToMemberPage(offset);
1396  memberoff = MXOffsetToMemberOffset(offset);
1397 
1398  if (pageno != prev_pageno)
1399  {
1400  slotno = SimpleLruReadPage(MultiXactMemberCtl, pageno, true, multi);
1401  prev_pageno = pageno;
1402  }
1403 
1404  xactptr = (TransactionId *)
1405  (MultiXactMemberCtl->shared->page_buffer[slotno] + memberoff);
1406 
1407  if (!TransactionIdIsValid(*xactptr))
1408  {
1409  /* Corner case 3: we must be looking at unused slot zero */
1410  Assert(offset == 0);
1411  continue;
1412  }
1413 
1414  flagsoff = MXOffsetToFlagsOffset(offset);
1415  bshift = MXOffsetToFlagsBitShift(offset);
1416  flagsptr = (uint32 *) (MultiXactMemberCtl->shared->page_buffer[slotno] + flagsoff);
1417 
1418  ptr[truelength].xid = *xactptr;
1419  ptr[truelength].status = (*flagsptr >> bshift) & MXACT_MEMBER_XACT_BITMASK;
1420  truelength++;
1421  }
1422 
1423  LWLockRelease(MultiXactMemberControlLock);
1424 
1425  /*
1426  * Copy the result into the local cache.
1427  */
1428  mXactCachePut(multi, truelength, ptr);
1429 
1430  debug_elog3(DEBUG2, "GetMembers: no cache for %s",
1431  mxid_to_string(multi, truelength, ptr));
1432  return truelength;
1433 }
1434 
1435 /*
1436  * mxactMemberComparator
1437  * qsort comparison function for MultiXactMember
1438  *
1439  * We can't use wraparound comparison for XIDs because that does not respect
1440  * the triangle inequality! Any old sort order will do.
1441  */
1442 static int
1443 mxactMemberComparator(const void *arg1, const void *arg2)
1444 {
1445  MultiXactMember member1 = *(const MultiXactMember *) arg1;
1446  MultiXactMember member2 = *(const MultiXactMember *) arg2;
1447 
1448  if (member1.xid > member2.xid)
1449  return 1;
1450  if (member1.xid < member2.xid)
1451  return -1;
1452  if (member1.status > member2.status)
1453  return 1;
1454  if (member1.status < member2.status)
1455  return -1;
1456  return 0;
1457 }
1458 
1459 /*
1460  * mXactCacheGetBySet
1461  * returns a MultiXactId from the cache based on the set of
1462  * TransactionIds that compose it, or InvalidMultiXactId if
1463  * none matches.
1464  *
1465  * This is helpful, for example, if two transactions want to lock a huge
1466  * table. By using the cache, the second will use the same MultiXactId
1467  * for the majority of tuples, thus keeping MultiXactId usage low (saving
1468  * both I/O and wraparound issues).
1469  *
1470  * NB: the passed members array will be sorted in-place.
1471  */
1472 static MultiXactId
1473 mXactCacheGetBySet(int nmembers, MultiXactMember *members)
1474 {
1475  dlist_iter iter;
1476 
1477  debug_elog3(DEBUG2, "CacheGet: looking for %s",
1478  mxid_to_string(InvalidMultiXactId, nmembers, members));
1479 
1480  /* sort the array so comparison is easy */
1481  qsort(members, nmembers, sizeof(MultiXactMember), mxactMemberComparator);
1482 
1483  dlist_foreach(iter, &MXactCache)
1484  {
1485  mXactCacheEnt *entry = dlist_container(mXactCacheEnt, node, iter.cur);
1486 
1487  if (entry->nmembers != nmembers)
1488  continue;
1489 
1490  /*
1491  * We assume the cache entries are sorted, and that the unused bits in
1492  * "status" are zeroed.
1493  */
1494  if (memcmp(members, entry->members, nmembers * sizeof(MultiXactMember)) == 0)
1495  {
1496  debug_elog3(DEBUG2, "CacheGet: found %u", entry->multi);
1497  dlist_move_head(&MXactCache, iter.cur);
1498  return entry->multi;
1499  }
1500  }
1501 
1502  debug_elog2(DEBUG2, "CacheGet: not found :-(");
1503  return InvalidMultiXactId;
1504 }
1505 
1506 /*
1507  * mXactCacheGetById
1508  * returns the composing MultiXactMember set from the cache for a
1509  * given MultiXactId, if present.
1510  *
1511  * If successful, *xids is set to the address of a palloc'd copy of the
1512  * MultiXactMember set. Return value is number of members, or -1 on failure.
1513  */
1514 static int
1516 {
1517  dlist_iter iter;
1518 
1519  debug_elog3(DEBUG2, "CacheGet: looking for %u", multi);
1520 
1521  dlist_foreach(iter, &MXactCache)
1522  {
1523  mXactCacheEnt *entry = dlist_container(mXactCacheEnt, node, iter.cur);
1524 
1525  if (entry->multi == multi)
1526  {
1527  MultiXactMember *ptr;
1528  Size size;
1529 
1530  size = sizeof(MultiXactMember) * entry->nmembers;
1531  ptr = (MultiXactMember *) palloc(size);
1532  *members = ptr;
1533 
1534  memcpy(ptr, entry->members, size);
1535 
1536  debug_elog3(DEBUG2, "CacheGet: found %s",
1537  mxid_to_string(multi,
1538  entry->nmembers,
1539  entry->members));
1540 
1541  /*
1542  * Note we modify the list while not using a modifiable iterator.
1543  * This is acceptable only because we exit the iteration
1544  * immediately afterwards.
1545  */
1546  dlist_move_head(&MXactCache, iter.cur);
1547 
1548  return entry->nmembers;
1549  }
1550  }
1551 
1552  debug_elog2(DEBUG2, "CacheGet: not found");
1553  return -1;
1554 }
1555 
1556 /*
1557  * mXactCachePut
1558  * Add a new MultiXactId and its composing set into the local cache.
1559  */
1560 static void
1561 mXactCachePut(MultiXactId multi, int nmembers, MultiXactMember *members)
1562 {
1563  mXactCacheEnt *entry;
1564 
1565  debug_elog3(DEBUG2, "CachePut: storing %s",
1566  mxid_to_string(multi, nmembers, members));
1567 
1568  if (MXactContext == NULL)
1569  {
1570  /* The cache only lives as long as the current transaction */
1571  debug_elog2(DEBUG2, "CachePut: initializing memory context");
1573  "MultiXact cache context",
1575  }
1576 
1577  entry = (mXactCacheEnt *)
1578  MemoryContextAlloc(MXactContext,
1579  offsetof(mXactCacheEnt, members) +
1580  nmembers * sizeof(MultiXactMember));
1581 
1582  entry->multi = multi;
1583  entry->nmembers = nmembers;
1584  memcpy(entry->members, members, nmembers * sizeof(MultiXactMember));
1585 
1586  /* mXactCacheGetBySet assumes the entries are sorted, so sort them */
1587  qsort(entry->members, nmembers, sizeof(MultiXactMember), mxactMemberComparator);
1588 
1589  dlist_push_head(&MXactCache, &entry->node);
1591  {
1592  dlist_node *node;
1593  mXactCacheEnt *entry;
1594 
1595  node = dlist_tail_node(&MXactCache);
1596  dlist_delete(node);
1598 
1599  entry = dlist_container(mXactCacheEnt, node, node);
1600  debug_elog3(DEBUG2, "CachePut: pruning cached multi %u",
1601  entry->multi);
1602 
1603  pfree(entry);
1604  }
1605 }
1606 
1607 static char *
1609 {
1610  switch (status)
1611  {
1613  return "keysh";
1615  return "sh";
1617  return "fornokeyupd";
1619  return "forupd";
1621  return "nokeyupd";
1622  case MultiXactStatusUpdate:
1623  return "upd";
1624  default:
1625  elog(ERROR, "unrecognized multixact status %d", status);
1626  return "";
1627  }
1628 }
1629 
1630 char *
1631 mxid_to_string(MultiXactId multi, int nmembers, MultiXactMember *members)
1632 {
1633  static char *str = NULL;
1635  int i;
1636 
1637  if (str != NULL)
1638  pfree(str);
1639 
1640  initStringInfo(&buf);
1641 
1642  appendStringInfo(&buf, "%u %d[%u (%s)", multi, nmembers, members[0].xid,
1643  mxstatus_to_string(members[0].status));
1644 
1645  for (i = 1; i < nmembers; i++)
1646  appendStringInfo(&buf, ", %u (%s)", members[i].xid,
1647  mxstatus_to_string(members[i].status));
1648 
1649  appendStringInfoChar(&buf, ']');
1651  pfree(buf.data);
1652  return str;
1653 }
1654 
1655 /*
1656  * AtEOXact_MultiXact
1657  * Handle transaction end for MultiXact
1658  *
1659  * This is called at top transaction commit or abort (we don't care which).
1660  */
1661 void
1663 {
1664  /*
1665  * Reset our OldestMemberMXactId and OldestVisibleMXactId values, both of
1666  * which should only be valid while within a transaction.
1667  *
1668  * We assume that storing a MultiXactId is atomic and so we need not take
1669  * MultiXactGenLock to do this.
1670  */
1673 
1674  /*
1675  * Discard the local MultiXactId cache. Since MXactContext was created as
1676  * a child of TopTransactionContext, we needn't delete it explicitly.
1677  */
1678  MXactContext = NULL;
1679  dlist_init(&MXactCache);
1680  MXactCacheMembers = 0;
1681 }
1682 
1683 /*
1684  * AtPrepare_MultiXact
1685  * Save multixact state at 2PC transaction prepare
1686  *
1687  * In this phase, we only store our OldestMemberMXactId value in the two-phase
1688  * state file.
1689  */
1690 void
1692 {
1693  MultiXactId myOldestMember = OldestMemberMXactId[MyBackendId];
1694 
1695  if (MultiXactIdIsValid(myOldestMember))
1697  &myOldestMember, sizeof(MultiXactId));
1698 }
1699 
1700 /*
1701  * PostPrepare_MultiXact
1702  * Clean up after successful PREPARE TRANSACTION
1703  */
1704 void
1706 {
1707  MultiXactId myOldestMember;
1708 
1709  /*
1710  * Transfer our OldestMemberMXactId value to the slot reserved for the
1711  * prepared transaction.
1712  */
1713  myOldestMember = OldestMemberMXactId[MyBackendId];
1714  if (MultiXactIdIsValid(myOldestMember))
1715  {
1716  BackendId dummyBackendId = TwoPhaseGetDummyBackendId(xid);
1717 
1718  /*
1719  * Even though storing MultiXactId is atomic, acquire lock to make
1720  * sure others see both changes, not just the reset of the slot of the
1721  * current backend. Using a volatile pointer might suffice, but this
1722  * isn't a hot spot.
1723  */
1724  LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
1725 
1726  OldestMemberMXactId[dummyBackendId] = myOldestMember;
1728 
1729  LWLockRelease(MultiXactGenLock);
1730  }
1731 
1732  /*
1733  * We don't need to transfer OldestVisibleMXactId value, because the
1734  * transaction is not going to be looking at any more multixacts once it's
1735  * prepared.
1736  *
1737  * We assume that storing a MultiXactId is atomic and so we need not take
1738  * MultiXactGenLock to do this.
1739  */
1741 
1742  /*
1743  * Discard the local MultiXactId cache like in AtEOX_MultiXact
1744  */
1745  MXactContext = NULL;
1746  dlist_init(&MXactCache);
1747  MXactCacheMembers = 0;
1748 }
1749 
1750 /*
1751  * multixact_twophase_recover
1752  * Recover the state of a prepared transaction at startup
1753  */
1754 void
1756  void *recdata, uint32 len)
1757 {
1758  BackendId dummyBackendId = TwoPhaseGetDummyBackendId(xid);
1759  MultiXactId oldestMember;
1760 
1761  /*
1762  * Get the oldest member XID from the state file record, and set it in the
1763  * OldestMemberMXactId slot reserved for this prepared transaction.
1764  */
1765  Assert(len == sizeof(MultiXactId));
1766  oldestMember = *((MultiXactId *) recdata);
1767 
1768  OldestMemberMXactId[dummyBackendId] = oldestMember;
1769 }
1770 
1771 /*
1772  * multixact_twophase_postcommit
1773  * Similar to AtEOX_MultiXact but for COMMIT PREPARED
1774  */
1775 void
1777  void *recdata, uint32 len)
1778 {
1779  BackendId dummyBackendId = TwoPhaseGetDummyBackendId(xid);
1780 
1781  Assert(len == sizeof(MultiXactId));
1782 
1783  OldestMemberMXactId[dummyBackendId] = InvalidMultiXactId;
1784 }
1785 
1786 /*
1787  * multixact_twophase_postabort
1788  * This is actually just the same as the COMMIT case.
1789  */
1790 void
1792  void *recdata, uint32 len)
1793 {
1794  multixact_twophase_postcommit(xid, info, recdata, len);
1795 }
1796 
1797 /*
1798  * Initialization of shared memory for MultiXact. We use two SLRU areas,
1799  * thus double memory. Also, reserve space for the shared MultiXactState
1800  * struct and the per-backend MultiXactId arrays (two of those, too).
1801  */
1802 Size
1804 {
1805  Size size;
1806 
1807  /* We need 2*MaxOldestSlot + 1 perBackendXactIds[] entries */
1808 #define SHARED_MULTIXACT_STATE_SIZE \
1809  add_size(offsetof(MultiXactStateData, perBackendXactIds) + sizeof(MultiXactId), \
1810  mul_size(sizeof(MultiXactId) * 2, MaxOldestSlot))
1811 
1815 
1816  return size;
1817 }
1818 
1819 void
1821 {
1822  bool found;
1823 
1824  debug_elog2(DEBUG2, "Shared Memory Init for MultiXact");
1825 
1828 
1830  "multixact_offset", NUM_MXACTOFFSET_BUFFERS, 0,
1831  MultiXactOffsetControlLock, "pg_multixact/offsets",
1834  "multixact_member", NUM_MXACTMEMBER_BUFFERS, 0,
1835  MultiXactMemberControlLock, "pg_multixact/members",
1837 
1838  /* Initialize our shared state struct */
1839  MultiXactState = ShmemInitStruct("Shared MultiXact State",
1841  &found);
1842  if (!IsUnderPostmaster)
1843  {
1844  Assert(!found);
1845 
1846  /* Make sure we zero out the per-backend state */
1847  MemSet(MultiXactState, 0, SHARED_MULTIXACT_STATE_SIZE);
1848  }
1849  else
1850  Assert(found);
1851 
1852  /*
1853  * Set up array pointers. Note that perBackendXactIds[0] is wasted space
1854  * since we only use indexes 1..MaxOldestSlot in each array.
1855  */
1856  OldestMemberMXactId = MultiXactState->perBackendXactIds;
1858 }
1859 
1860 /*
1861  * This func must be called ONCE on system install. It creates the initial
1862  * MultiXact segments. (The MultiXacts directories are assumed to have been
1863  * created by initdb, and MultiXactShmemInit must have been called already.)
1864  */
1865 void
1867 {
1868  int slotno;
1869 
1870  LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
1871 
1872  /* Create and zero the first page of the offsets log */
1873  slotno = ZeroMultiXactOffsetPage(0, false);
1874 
1875  /* Make sure it's written out */
1877  Assert(!MultiXactOffsetCtl->shared->page_dirty[slotno]);
1878 
1879  LWLockRelease(MultiXactOffsetControlLock);
1880 
1881  LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
1882 
1883  /* Create and zero the first page of the members log */
1884  slotno = ZeroMultiXactMemberPage(0, false);
1885 
1886  /* Make sure it's written out */
1888  Assert(!MultiXactMemberCtl->shared->page_dirty[slotno]);
1889 
1890  LWLockRelease(MultiXactMemberControlLock);
1891 }
1892 
1893 /*
1894  * Initialize (or reinitialize) a page of MultiXactOffset to zeroes.
1895  * If writeXlog is TRUE, also emit an XLOG record saying we did this.
1896  *
1897  * The page is not actually written, just set up in shared memory.
1898  * The slot number of the new page is returned.
1899  *
1900  * Control lock must be held at entry, and will be held at exit.
1901  */
1902 static int
1903 ZeroMultiXactOffsetPage(int pageno, bool writeXlog)
1904 {
1905  int slotno;
1906 
1907  slotno = SimpleLruZeroPage(MultiXactOffsetCtl, pageno);
1908 
1909  if (writeXlog)
1911 
1912  return slotno;
1913 }
1914 
1915 /*
1916  * Ditto, for MultiXactMember
1917  */
1918 static int
1919 ZeroMultiXactMemberPage(int pageno, bool writeXlog)
1920 {
1921  int slotno;
1922 
1923  slotno = SimpleLruZeroPage(MultiXactMemberCtl, pageno);
1924 
1925  if (writeXlog)
1927 
1928  return slotno;
1929 }
1930 
1931 /*
1932  * MaybeExtendOffsetSlru
1933  * Extend the offsets SLRU area, if necessary
1934  *
1935  * After a binary upgrade from <= 9.2, the pg_multixact/offset SLRU area might
1936  * contain files that are shorter than necessary; this would occur if the old
1937  * installation had used multixacts beyond the first page (files cannot be
1938  * copied, because the on-disk representation is different). pg_upgrade would
1939  * update pg_control to set the next offset value to be at that position, so
1940  * that tuples marked as locked by such MultiXacts would be seen as visible
1941  * without having to consult multixact. However, trying to create and use a
1942  * new MultiXactId would result in an error because the page on which the new
1943  * value would reside does not exist. This routine is in charge of creating
1944  * such pages.
1945  */
1946 static void
1948 {
1949  int pageno;
1950 
1951  pageno = MultiXactIdToOffsetPage(MultiXactState->nextMXact);
1952 
1953  LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
1954 
1956  {
1957  int slotno;
1958 
1959  /*
1960  * Fortunately for us, SimpleLruWritePage is already prepared to deal
1961  * with creating a new segment file even if the page we're writing is
1962  * not the first in it, so this is enough.
1963  */
1964  slotno = ZeroMultiXactOffsetPage(pageno, false);
1966  }
1967 
1968  LWLockRelease(MultiXactOffsetControlLock);
1969 }
1970 
1971 /*
1972  * This must be called ONCE during postmaster or standalone-backend startup.
1973  *
1974  * StartupXLOG has already established nextMXact/nextOffset by calling
1975  * MultiXactSetNextMXact and/or MultiXactAdvanceNextMXact, and the oldestMulti
1976  * info from pg_control and/or MultiXactAdvanceOldest, but we haven't yet
1977  * replayed WAL.
1978  */
1979 void
1981 {
1982  MultiXactId multi = MultiXactState->nextMXact;
1983  MultiXactOffset offset = MultiXactState->nextOffset;
1984  int pageno;
1985 
1986  /*
1987  * Initialize offset's idea of the latest page number.
1988  */
1989  pageno = MultiXactIdToOffsetPage(multi);
1990  MultiXactOffsetCtl->shared->latest_page_number = pageno;
1991 
1992  /*
1993  * Initialize member's idea of the latest page number.
1994  */
1995  pageno = MXOffsetToMemberPage(offset);
1996  MultiXactMemberCtl->shared->latest_page_number = pageno;
1997 }
1998 
1999 /*
2000  * This must be called ONCE at the end of startup/recovery.
2001  */
2002 void
2004 {
2005  MultiXactId nextMXact;
2006  MultiXactOffset offset;
2007  MultiXactId oldestMXact;
2008  Oid oldestMXactDB;
2009  int pageno;
2010  int entryno;
2011  int flagsoff;
2012 
2013  LWLockAcquire(MultiXactGenLock, LW_SHARED);
2014  nextMXact = MultiXactState->nextMXact;
2015  offset = MultiXactState->nextOffset;
2016  oldestMXact = MultiXactState->oldestMultiXactId;
2017  oldestMXactDB = MultiXactState->oldestMultiXactDB;
2018  LWLockRelease(MultiXactGenLock);
2019 
2020  /* Clean up offsets state */
2021  LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
2022 
2023  /*
2024  * (Re-)Initialize our idea of the latest page number for offsets.
2025  */
2026  pageno = MultiXactIdToOffsetPage(nextMXact);
2027  MultiXactOffsetCtl->shared->latest_page_number = pageno;
2028 
2029  /*
2030  * Zero out the remainder of the current offsets page. See notes in
2031  * TrimCLOG() for background. Unlike CLOG, some WAL record covers every
2032  * pg_multixact SLRU mutation. Since, also unlike CLOG, we ignore the WAL
2033  * rule "write xlog before data," nextMXact successors may carry obsolete,
2034  * nonzero offset values. Zero those so case 2 of GetMultiXactIdMembers()
2035  * operates normally.
2036  */
2037  entryno = MultiXactIdToOffsetEntry(nextMXact);
2038  if (entryno != 0)
2039  {
2040  int slotno;
2041  MultiXactOffset *offptr;
2042 
2043  slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, nextMXact);
2044  offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
2045  offptr += entryno;
2046 
2047  MemSet(offptr, 0, BLCKSZ - (entryno * sizeof(MultiXactOffset)));
2048 
2049  MultiXactOffsetCtl->shared->page_dirty[slotno] = true;
2050  }
2051 
2052  LWLockRelease(MultiXactOffsetControlLock);
2053 
2054  /* And the same for members */
2055  LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
2056 
2057  /*
2058  * (Re-)Initialize our idea of the latest page number for members.
2059  */
2060  pageno = MXOffsetToMemberPage(offset);
2061  MultiXactMemberCtl->shared->latest_page_number = pageno;
2062 
2063  /*
2064  * Zero out the remainder of the current members page. See notes in
2065  * TrimCLOG() for motivation.
2066  */
2067  flagsoff = MXOffsetToFlagsOffset(offset);
2068  if (flagsoff != 0)
2069  {
2070  int slotno;
2071  TransactionId *xidptr;
2072  int memberoff;
2073 
2074  memberoff = MXOffsetToMemberOffset(offset);
2075  slotno = SimpleLruReadPage(MultiXactMemberCtl, pageno, true, offset);
2076  xidptr = (TransactionId *)
2077  (MultiXactMemberCtl->shared->page_buffer[slotno] + memberoff);
2078 
2079  MemSet(xidptr, 0, BLCKSZ - memberoff);
2080 
2081  /*
2082  * Note: we don't need to zero out the flag bits in the remaining
2083  * members of the current group, because they are always reset before
2084  * writing.
2085  */
2086 
2087  MultiXactMemberCtl->shared->page_dirty[slotno] = true;
2088  }
2089 
2090  LWLockRelease(MultiXactMemberControlLock);
2091 
2092  /* signal that we're officially up */
2093  LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
2094  MultiXactState->finishedStartup = true;
2095  LWLockRelease(MultiXactGenLock);
2096 
2097  /* Now compute how far away the next members wraparound is. */
2098  SetMultiXactIdLimit(oldestMXact, oldestMXactDB, true);
2099 }
2100 
2101 /*
2102  * This must be called ONCE during postmaster or standalone-backend shutdown
2103  */
2104 void
2106 {
2107  /* Flush dirty MultiXact pages to disk */
2108  TRACE_POSTGRESQL_MULTIXACT_CHECKPOINT_START(false);
2111  TRACE_POSTGRESQL_MULTIXACT_CHECKPOINT_DONE(false);
2112 }
2113 
2114 /*
2115  * Get the MultiXact data to save in a checkpoint record
2116  */
2117 void
2118 MultiXactGetCheckptMulti(bool is_shutdown,
2119  MultiXactId *nextMulti,
2120  MultiXactOffset *nextMultiOffset,
2121  MultiXactId *oldestMulti,
2122  Oid *oldestMultiDB)
2123 {
2124  LWLockAcquire(MultiXactGenLock, LW_SHARED);
2125  *nextMulti = MultiXactState->nextMXact;
2126  *nextMultiOffset = MultiXactState->nextOffset;
2127  *oldestMulti = MultiXactState->oldestMultiXactId;
2128  *oldestMultiDB = MultiXactState->oldestMultiXactDB;
2129  LWLockRelease(MultiXactGenLock);
2130 
2132  "MultiXact: checkpoint is nextMulti %u, nextOffset %u, oldestMulti %u in DB %u",
2133  *nextMulti, *nextMultiOffset, *oldestMulti, *oldestMultiDB);
2134 }
2135 
2136 /*
2137  * Perform a checkpoint --- either during shutdown, or on-the-fly
2138  */
2139 void
2141 {
2142  TRACE_POSTGRESQL_MULTIXACT_CHECKPOINT_START(true);
2143 
2144  /* Flush dirty MultiXact pages to disk */
2147 
2148  TRACE_POSTGRESQL_MULTIXACT_CHECKPOINT_DONE(true);
2149 }
2150 
2151 /*
2152  * Set the next-to-be-assigned MultiXactId and offset
2153  *
2154  * This is used when we can determine the correct next ID/offset exactly
2155  * from a checkpoint record. Although this is only called during bootstrap
2156  * and XLog replay, we take the lock in case any hot-standby backends are
2157  * examining the values.
2158  */
2159 void
2161  MultiXactOffset nextMultiOffset)
2162 {
2163  debug_elog4(DEBUG2, "MultiXact: setting next multi to %u offset %u",
2164  nextMulti, nextMultiOffset);
2165  LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
2166  MultiXactState->nextMXact = nextMulti;
2167  MultiXactState->nextOffset = nextMultiOffset;
2168  LWLockRelease(MultiXactGenLock);
2169 
2170  /*
2171  * During a binary upgrade, make sure that the offsets SLRU is large
2172  * enough to contain the next value that would be created.
2173  *
2174  * We need to do this pretty early during the first startup in binary
2175  * upgrade mode: before StartupMultiXact() in fact, because this routine
2176  * is called even before that by StartupXLOG(). And we can't do it
2177  * earlier than at this point, because during that first call of this
2178  * routine we determine the MultiXactState->nextMXact value that
2179  * MaybeExtendOffsetSlru needs.
2180  */
2181  if (IsBinaryUpgrade)
2183 }
2184 
2185 /*
2186  * Determine the last safe MultiXactId to allocate given the currently oldest
2187  * datminmxid (ie, the oldest MultiXactId that might exist in any database
2188  * of our cluster), and the OID of the (or a) database with that value.
2189  *
2190  * is_startup is true when we are just starting the cluster, false when we
2191  * are updating state in a running cluster. This only affects log messages.
2192  */
2193 void
2194 SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid,
2195  bool is_startup)
2196 {
2197  MultiXactId multiVacLimit;
2198  MultiXactId multiWarnLimit;
2199  MultiXactId multiStopLimit;
2200  MultiXactId multiWrapLimit;
2201  MultiXactId curMulti;
2202  bool needs_offset_vacuum;
2203 
2204  Assert(MultiXactIdIsValid(oldest_datminmxid));
2205 
2206  /*
2207  * We pretend that a wrap will happen halfway through the multixact ID
2208  * space, but that's not really true, because multixacts wrap differently
2209  * from transaction IDs. Note that, separately from any concern about
2210  * multixact IDs wrapping, we must ensure that multixact members do not
2211  * wrap. Limits for that are set in DetermineSafeOldestOffset, not here.
2212  */
2213  multiWrapLimit = oldest_datminmxid + (MaxMultiXactId >> 1);
2214  if (multiWrapLimit < FirstMultiXactId)
2215  multiWrapLimit += FirstMultiXactId;
2216 
2217  /*
2218  * We'll refuse to continue assigning MultiXactIds once we get within 100
2219  * multi of data loss.
2220  *
2221  * Note: This differs from the magic number used in
2222  * SetTransactionIdLimit() since vacuum itself will never generate new
2223  * multis. XXX actually it does, if it needs to freeze old multis.
2224  */
2225  multiStopLimit = multiWrapLimit - 100;
2226  if (multiStopLimit < FirstMultiXactId)
2227  multiStopLimit -= FirstMultiXactId;
2228 
2229  /*
2230  * We'll start complaining loudly when we get within 10M multis of the
2231  * stop point. This is kind of arbitrary, but if you let your gas gauge
2232  * get down to 1% of full, would you be looking for the next gas station?
2233  * We need to be fairly liberal about this number because there are lots
2234  * of scenarios where most transactions are done by automatic clients that
2235  * won't pay attention to warnings. (No, we're not gonna make this
2236  * configurable. If you know enough to configure it, you know enough to
2237  * not get in this kind of trouble in the first place.)
2238  */
2239  multiWarnLimit = multiStopLimit - 10000000;
2240  if (multiWarnLimit < FirstMultiXactId)
2241  multiWarnLimit -= FirstMultiXactId;
2242 
2243  /*
2244  * We'll start trying to force autovacuums when oldest_datminmxid gets to
2245  * be more than autovacuum_multixact_freeze_max_age mxids old.
2246  *
2247  * Note: autovacuum_multixact_freeze_max_age is a PGC_POSTMASTER parameter
2248  * so that we don't have to worry about dealing with on-the-fly changes in
2249  * its value. See SetTransactionIdLimit.
2250  */
2251  multiVacLimit = oldest_datminmxid + autovacuum_multixact_freeze_max_age;
2252  if (multiVacLimit < FirstMultiXactId)
2253  multiVacLimit += FirstMultiXactId;
2254 
2255  /* Grab lock for just long enough to set the new limit values */
2256  LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
2257  MultiXactState->oldestMultiXactId = oldest_datminmxid;
2258  MultiXactState->oldestMultiXactDB = oldest_datoid;
2259  MultiXactState->multiVacLimit = multiVacLimit;
2260  MultiXactState->multiWarnLimit = multiWarnLimit;
2261  MultiXactState->multiStopLimit = multiStopLimit;
2262  MultiXactState->multiWrapLimit = multiWrapLimit;
2263  curMulti = MultiXactState->nextMXact;
2264  LWLockRelease(MultiXactGenLock);
2265 
2266  /* Log the info */
2267  ereport(DEBUG1,
2268  (errmsg("MultiXactId wrap limit is %u, limited by database with OID %u",
2269  multiWrapLimit, oldest_datoid)));
2270 
2271  /*
2272  * Computing the actual limits is only possible once the data directory is
2273  * in a consistent state. There's no need to compute the limits while
2274  * still replaying WAL - no decisions about new multis are made even
2275  * though multixact creations might be replayed. So we'll only do further
2276  * checks after TrimMultiXact() has been called.
2277  */
2278  if (!MultiXactState->finishedStartup)
2279  return;
2280 
2281  Assert(!InRecovery);
2282 
2283  /* Set limits for offset vacuum. */
2284  needs_offset_vacuum = SetOffsetVacuumLimit(is_startup);
2285 
2286  /*
2287  * If past the autovacuum force point, immediately signal an autovac
2288  * request. The reason for this is that autovac only processes one
2289  * database per invocation. Once it's finished cleaning up the oldest
2290  * database, it'll call here, and we'll signal the postmaster to start
2291  * another iteration immediately if there are still any old databases.
2292  */
2293  if ((MultiXactIdPrecedes(multiVacLimit, curMulti) ||
2294  needs_offset_vacuum) && IsUnderPostmaster)
2296 
2297  /* Give an immediate warning if past the wrap warn point */
2298  if (MultiXactIdPrecedes(multiWarnLimit, curMulti))
2299  {
2300  char *oldest_datname;
2301 
2302  /*
2303  * We can be called when not inside a transaction, for example during
2304  * StartupXLOG(). In such a case we cannot do database access, so we
2305  * must just report the oldest DB's OID.
2306  *
2307  * Note: it's also possible that get_database_name fails and returns
2308  * NULL, for example because the database just got dropped. We'll
2309  * still warn, even though the warning might now be unnecessary.
2310  */
2311  if (IsTransactionState())
2312  oldest_datname = get_database_name(oldest_datoid);
2313  else
2314  oldest_datname = NULL;
2315 
2316  if (oldest_datname)
2317  ereport(WARNING,
2318  (errmsg_plural("database \"%s\" must be vacuumed before %u more MultiXactId is used",
2319  "database \"%s\" must be vacuumed before %u more MultiXactIds are used",
2320  multiWrapLimit - curMulti,
2321  oldest_datname,
2322  multiWrapLimit - curMulti),
2323  errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
2324  "You might also need to commit or roll back old prepared transactions.")));
2325  else
2326  ereport(WARNING,
2327  (errmsg_plural("database with OID %u must be vacuumed before %u more MultiXactId is used",
2328  "database with OID %u must be vacuumed before %u more MultiXactIds are used",
2329  multiWrapLimit - curMulti,
2330  oldest_datoid,
2331  multiWrapLimit - curMulti),
2332  errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
2333  "You might also need to commit or roll back old prepared transactions.")));
2334  }
2335 }
2336 
2337 /*
2338  * Ensure the next-to-be-assigned MultiXactId is at least minMulti,
2339  * and similarly nextOffset is at least minMultiOffset.
2340  *
2341  * This is used when we can determine minimum safe values from an XLog
2342  * record (either an on-line checkpoint or an mxact creation log entry).
2343  * Although this is only called during XLog replay, we take the lock in case
2344  * any hot-standby backends are examining the values.
2345  */
2346 void
2348  MultiXactOffset minMultiOffset)
2349 {
2350  LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
2351  if (MultiXactIdPrecedes(MultiXactState->nextMXact, minMulti))
2352  {
2353  debug_elog3(DEBUG2, "MultiXact: setting next multi to %u", minMulti);
2354  MultiXactState->nextMXact = minMulti;
2355  }
2356  if (MultiXactOffsetPrecedes(MultiXactState->nextOffset, minMultiOffset))
2357  {
2358  debug_elog3(DEBUG2, "MultiXact: setting next offset to %u",
2359  minMultiOffset);
2360  MultiXactState->nextOffset = minMultiOffset;
2361  }
2362  LWLockRelease(MultiXactGenLock);
2363 }
2364 
2365 /*
2366  * Update our oldestMultiXactId value, but only if it's more recent than what
2367  * we had.
2368  *
2369  * This may only be called during WAL replay.
2370  */
2371 void
2372 MultiXactAdvanceOldest(MultiXactId oldestMulti, Oid oldestMultiDB)
2373 {
2374  Assert(InRecovery);
2375 
2376  if (MultiXactIdPrecedes(MultiXactState->oldestMultiXactId, oldestMulti))
2377  SetMultiXactIdLimit(oldestMulti, oldestMultiDB, false);
2378 }
2379 
2380 /*
2381  * Make sure that MultiXactOffset has room for a newly-allocated MultiXactId.
2382  *
2383  * NB: this is called while holding MultiXactGenLock. We want it to be very
2384  * fast most of the time; even when it's not so fast, no actual I/O need
2385  * happen unless we're forced to write out a dirty log or xlog page to make
2386  * room in shared memory.
2387  */
2388 static void
2390 {
2391  int pageno;
2392 
2393  /*
2394  * No work except at first MultiXactId of a page. But beware: just after
2395  * wraparound, the first MultiXactId of page zero is FirstMultiXactId.
2396  */
2397  if (MultiXactIdToOffsetEntry(multi) != 0 &&
2398  multi != FirstMultiXactId)
2399  return;
2400 
2401  pageno = MultiXactIdToOffsetPage(multi);
2402 
2403  LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
2404 
2405  /* Zero the page and make an XLOG entry about it */
2406  ZeroMultiXactOffsetPage(pageno, true);
2407 
2408  LWLockRelease(MultiXactOffsetControlLock);
2409 }
2410 
2411 /*
2412  * Make sure that MultiXactMember has room for the members of a newly-
2413  * allocated MultiXactId.
2414  *
2415  * Like the above routine, this is called while holding MultiXactGenLock;
2416  * same comments apply.
2417  */
2418 static void
2420 {
2421  /*
2422  * It's possible that the members span more than one page of the members
2423  * file, so we loop to ensure we consider each page. The coding is not
2424  * optimal if the members span several pages, but that seems unusual
2425  * enough to not worry much about.
2426  */
2427  while (nmembers > 0)
2428  {
2429  int flagsoff;
2430  int flagsbit;
2432 
2433  /*
2434  * Only zero when at first entry of a page.
2435  */
2436  flagsoff = MXOffsetToFlagsOffset(offset);
2437  flagsbit = MXOffsetToFlagsBitShift(offset);
2438  if (flagsoff == 0 && flagsbit == 0)
2439  {
2440  int pageno;
2441 
2442  pageno = MXOffsetToMemberPage(offset);
2443 
2444  LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
2445 
2446  /* Zero the page and make an XLOG entry about it */
2447  ZeroMultiXactMemberPage(pageno, true);
2448 
2449  LWLockRelease(MultiXactMemberControlLock);
2450  }
2451 
2452  /*
2453  * Compute the number of items till end of current page. Careful: if
2454  * addition of unsigned ints wraps around, we're at the last page of
2455  * the last segment; since that page holds a different number of items
2456  * than other pages, we need to do it differently.
2457  */
2458  if (offset + MAX_MEMBERS_IN_LAST_MEMBERS_PAGE < offset)
2459  {
2460  /*
2461  * This is the last page of the last segment; we can compute the
2462  * number of items left to allocate in it without modulo
2463  * arithmetic.
2464  */
2465  difference = MaxMultiXactOffset - offset + 1;
2466  }
2467  else
2469 
2470  /*
2471  * Advance to next page, taking care to properly handle the wraparound
2472  * case. OK if nmembers goes negative.
2473  */
2474  nmembers -= difference;
2475  offset += difference;
2476  }
2477 }
2478 
2479 /*
2480  * GetOldestMultiXactId
2481  *
2482  * Return the oldest MultiXactId that's still possibly still seen as live by
2483  * any running transaction. Older ones might still exist on disk, but they no
2484  * longer have any running member transaction.
2485  *
2486  * It's not safe to truncate MultiXact SLRU segments on the value returned by
2487  * this function; however, it can be used by a full-table vacuum to set the
2488  * point at which it will be possible to truncate SLRU for that table.
2489  */
2492 {
2493  MultiXactId oldestMXact;
2494  MultiXactId nextMXact;
2495  int i;
2496 
2497  /*
2498  * This is the oldest valid value among all the OldestMemberMXactId[] and
2499  * OldestVisibleMXactId[] entries, or nextMXact if none are valid.
2500  */
2501  LWLockAcquire(MultiXactGenLock, LW_SHARED);
2502 
2503  /*
2504  * We have to beware of the possibility that nextMXact is in the
2505  * wrapped-around state. We don't fix the counter itself here, but we
2506  * must be sure to use a valid value in our calculation.
2507  */
2508  nextMXact = MultiXactState->nextMXact;
2509  if (nextMXact < FirstMultiXactId)
2510  nextMXact = FirstMultiXactId;
2511 
2512  oldestMXact = nextMXact;
2513  for (i = 1; i <= MaxOldestSlot; i++)
2514  {
2515  MultiXactId thisoldest;
2516 
2517  thisoldest = OldestMemberMXactId[i];
2518  if (MultiXactIdIsValid(thisoldest) &&
2519  MultiXactIdPrecedes(thisoldest, oldestMXact))
2520  oldestMXact = thisoldest;
2521  thisoldest = OldestVisibleMXactId[i];
2522  if (MultiXactIdIsValid(thisoldest) &&
2523  MultiXactIdPrecedes(thisoldest, oldestMXact))
2524  oldestMXact = thisoldest;
2525  }
2526 
2527  LWLockRelease(MultiXactGenLock);
2528 
2529  return oldestMXact;
2530 }
2531 
2532 /*
2533  * Determine how aggressively we need to vacuum in order to prevent member
2534  * wraparound.
2535  *
2536  * To do so determine what's the oldest member offset and install the limit
2537  * info in MultiXactState, where it can be used to prevent overrun of old data
2538  * in the members SLRU area.
2539  *
2540  * The return value is true if emergency autovacuum is required and false
2541  * otherwise.
2542  */
2543 static bool
2544 SetOffsetVacuumLimit(bool is_startup)
2545 {
2546  MultiXactId oldestMultiXactId;
2547  MultiXactId nextMXact;
2548  MultiXactOffset oldestOffset = 0; /* placate compiler */
2549  MultiXactOffset prevOldestOffset;
2550  MultiXactOffset nextOffset;
2551  bool oldestOffsetKnown = false;
2552  bool prevOldestOffsetKnown;
2553  MultiXactOffset offsetStopLimit = 0;
2554  MultiXactOffset prevOffsetStopLimit;
2555 
2556  /*
2557  * NB: Have to prevent concurrent truncation, we might otherwise try to
2558  * lookup a oldestMulti that's concurrently getting truncated away.
2559  */
2560  LWLockAcquire(MultiXactTruncationLock, LW_SHARED);
2561 
2562  /* Read relevant fields from shared memory. */
2563  LWLockAcquire(MultiXactGenLock, LW_SHARED);
2564  oldestMultiXactId = MultiXactState->oldestMultiXactId;
2565  nextMXact = MultiXactState->nextMXact;
2566  nextOffset = MultiXactState->nextOffset;
2567  prevOldestOffsetKnown = MultiXactState->oldestOffsetKnown;
2568  prevOldestOffset = MultiXactState->oldestOffset;
2569  prevOffsetStopLimit = MultiXactState->offsetStopLimit;
2570  Assert(MultiXactState->finishedStartup);
2571  LWLockRelease(MultiXactGenLock);
2572 
2573  /*
2574  * Determine the offset of the oldest multixact. Normally, we can read
2575  * the offset from the multixact itself, but there's an important special
2576  * case: if there are no multixacts in existence at all, oldestMXact
2577  * obviously can't point to one. It will instead point to the multixact
2578  * ID that will be assigned the next time one is needed.
2579  */
2580  if (oldestMultiXactId == nextMXact)
2581  {
2582  /*
2583  * When the next multixact gets created, it will be stored at the next
2584  * offset.
2585  */
2586  oldestOffset = nextOffset;
2587  oldestOffsetKnown = true;
2588  }
2589  else
2590  {
2591  /*
2592  * Figure out where the oldest existing multixact's offsets are
2593  * stored. Due to bugs in early release of PostgreSQL 9.3.X and 9.4.X,
2594  * the supposedly-earliest multixact might not really exist. We are
2595  * careful not to fail in that case.
2596  */
2597  oldestOffsetKnown =
2598  find_multixact_start(oldestMultiXactId, &oldestOffset);
2599 
2600  if (oldestOffsetKnown)
2601  ereport(DEBUG1,
2602  (errmsg("oldest MultiXactId member is at offset %u",
2603  oldestOffset)));
2604  else
2605  ereport(LOG,
2606  (errmsg("MultiXact member wraparound protections are disabled because oldest checkpointed MultiXact %u does not exist on disk",
2607  oldestMultiXactId)));
2608  }
2609 
2610  LWLockRelease(MultiXactTruncationLock);
2611 
2612  /*
2613  * If we can, compute limits (and install them MultiXactState) to prevent
2614  * overrun of old data in the members SLRU area. We can only do so if the
2615  * oldest offset is known though.
2616  */
2617  if (oldestOffsetKnown)
2618  {
2619  /* move back to start of the corresponding segment */
2620  offsetStopLimit = oldestOffset - (oldestOffset %
2622 
2623  /* always leave one segment before the wraparound point */
2624  offsetStopLimit -= (MULTIXACT_MEMBERS_PER_PAGE * SLRU_PAGES_PER_SEGMENT);
2625 
2626  if (!prevOldestOffsetKnown && !is_startup)
2627  ereport(LOG,
2628  (errmsg("MultiXact member wraparound protections are now enabled")));
2629 
2630  ereport(DEBUG1,
2631  (errmsg("MultiXact member stop limit is now %u based on MultiXact %u",
2632  offsetStopLimit, oldestMultiXactId)));
2633  }
2634  else if (prevOldestOffsetKnown)
2635  {
2636  /*
2637  * If we failed to get the oldest offset this time, but we have a
2638  * value from a previous pass through this function, use the old
2639  * values rather than automatically forcing an emergency autovacuum
2640  * cycle again.
2641  */
2642  oldestOffset = prevOldestOffset;
2643  oldestOffsetKnown = true;
2644  offsetStopLimit = prevOffsetStopLimit;
2645  }
2646 
2647  /* Install the computed values */
2648  LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
2649  MultiXactState->oldestOffset = oldestOffset;
2650  MultiXactState->oldestOffsetKnown = oldestOffsetKnown;
2651  MultiXactState->offsetStopLimit = offsetStopLimit;
2652  LWLockRelease(MultiXactGenLock);
2653 
2654  /*
2655  * Do we need an emergency autovacuum? If we're not sure, assume yes.
2656  */
2657  return !oldestOffsetKnown ||
2658  (nextOffset - oldestOffset > MULTIXACT_MEMBER_SAFE_THRESHOLD);
2659 }
2660 
2661 /*
2662  * Return whether adding "distance" to "start" would move past "boundary".
2663  *
2664  * We use this to determine whether the addition is "wrapping around" the
2665  * boundary point, hence the name. The reason we don't want to use the regular
2666  * 2^31-modulo arithmetic here is that we want to be able to use the whole of
2667  * the 2^32-1 space here, allowing for more multixacts that would fit
2668  * otherwise.
2669  */
2670 static bool
2672  uint32 distance)
2673 {
2674  MultiXactOffset finish;
2675 
2676  /*
2677  * Note that offset number 0 is not used (see GetMultiXactIdMembers), so
2678  * if the addition wraps around the UINT_MAX boundary, skip that value.
2679  */
2680  finish = start + distance;
2681  if (finish < start)
2682  finish++;
2683 
2684  /*-----------------------------------------------------------------------
2685  * When the boundary is numerically greater than the starting point, any
2686  * value numerically between the two is not wrapped:
2687  *
2688  * <----S----B---->
2689  * [---) = F wrapped past B (and UINT_MAX)
2690  * [---) = F not wrapped
2691  * [----] = F wrapped past B
2692  *
2693  * When the boundary is numerically less than the starting point (i.e. the
2694  * UINT_MAX wraparound occurs somewhere in between) then all values in
2695  * between are wrapped:
2696  *
2697  * <----B----S---->
2698  * [---) = F not wrapped past B (but wrapped past UINT_MAX)
2699  * [---) = F wrapped past B (and UINT_MAX)
2700  * [----] = F not wrapped
2701  *-----------------------------------------------------------------------
2702  */
2703  if (start < boundary)
2704  return finish >= boundary || finish < start;
2705  else
2706  return finish >= boundary && finish < start;
2707 }
2708 
2709 /*
2710  * Find the starting offset of the given MultiXactId.
2711  *
2712  * Returns false if the file containing the multi does not exist on disk.
2713  * Otherwise, returns true and sets *result to the starting member offset.
2714  *
2715  * This function does not prevent concurrent truncation, so if that's
2716  * required, the caller has to protect against that.
2717  */
2718 static bool
2720 {
2721  MultiXactOffset offset;
2722  int pageno;
2723  int entryno;
2724  int slotno;
2725  MultiXactOffset *offptr;
2726 
2727  Assert(MultiXactState->finishedStartup);
2728 
2729  pageno = MultiXactIdToOffsetPage(multi);
2730  entryno = MultiXactIdToOffsetEntry(multi);
2731 
2732  /*
2733  * Flush out dirty data, so PhysicalPageExists can work correctly.
2734  * SimpleLruFlush() is a pretty big hammer for that. Alternatively we
2735  * could add a in-memory version of page exists, but find_multixact_start
2736  * is called infrequently, and it doesn't seem bad to flush buffers to
2737  * disk before truncation.
2738  */
2741 
2743  return false;
2744 
2745  /* lock is acquired by SimpleLruReadPage_ReadOnly */
2746  slotno = SimpleLruReadPage_ReadOnly(MultiXactOffsetCtl, pageno, multi);
2747  offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
2748  offptr += entryno;
2749  offset = *offptr;
2750  LWLockRelease(MultiXactOffsetControlLock);
2751 
2752  *result = offset;
2753  return true;
2754 }
2755 
2756 /*
2757  * Determine how many multixacts, and how many multixact members, currently
2758  * exist. Return false if unable to determine.
2759  */
2760 static bool
2762 {
2763  MultiXactOffset nextOffset;
2764  MultiXactOffset oldestOffset;
2765  MultiXactId oldestMultiXactId;
2766  MultiXactId nextMultiXactId;
2767  bool oldestOffsetKnown;
2768 
2769  LWLockAcquire(MultiXactGenLock, LW_SHARED);
2770  nextOffset = MultiXactState->nextOffset;
2771  oldestMultiXactId = MultiXactState->oldestMultiXactId;
2772  nextMultiXactId = MultiXactState->nextMXact;
2773  oldestOffset = MultiXactState->oldestOffset;
2774  oldestOffsetKnown = MultiXactState->oldestOffsetKnown;
2775  LWLockRelease(MultiXactGenLock);
2776 
2777  if (!oldestOffsetKnown)
2778  return false;
2779 
2780  *members = nextOffset - oldestOffset;
2781  *multixacts = nextMultiXactId - oldestMultiXactId;
2782  return true;
2783 }
2784 
2785 /*
2786  * Multixact members can be removed once the multixacts that refer to them
2787  * are older than every datminxmid. autovacuum_multixact_freeze_max_age and
2788  * vacuum_multixact_freeze_table_age work together to make sure we never have
2789  * too many multixacts; we hope that, at least under normal circumstances,
2790  * this will also be sufficient to keep us from using too many offsets.
2791  * However, if the average multixact has many members, we might exhaust the
2792  * members space while still using few enough members that these limits fail
2793  * to trigger full table scans for relminmxid advancement. At that point,
2794  * we'd have no choice but to start failing multixact-creating operations
2795  * with an error.
2796  *
2797  * To prevent that, if more than a threshold portion of the members space is
2798  * used, we effectively reduce autovacuum_multixact_freeze_max_age and
2799  * to a value just less than the number of multixacts in use. We hope that
2800  * this will quickly trigger autovacuuming on the table or tables with the
2801  * oldest relminmxid, thus allowing datminmxid values to advance and removing
2802  * some members.
2803  *
2804  * As the fraction of the member space currently in use grows, we become
2805  * more aggressive in clamping this value. That not only causes autovacuum
2806  * to ramp up, but also makes any manual vacuums the user issues more
2807  * aggressive. This happens because vacuum_set_xid_limits() clamps the
2808  * freeze table and the minimum freeze age based on the effective
2809  * autovacuum_multixact_freeze_max_age this function returns. In the worst
2810  * case, we'll claim the freeze_max_age to zero, and every vacuum of any
2811  * table will try to freeze every multixact.
2812  *
2813  * It's possible that these thresholds should be user-tunable, but for now
2814  * we keep it simple.
2815  */
2816 int
2818 {
2819  MultiXactOffset members;
2820  uint32 multixacts;
2821  uint32 victim_multixacts;
2822  double fraction;
2823 
2824  /* If we can't determine member space utilization, assume the worst. */
2825  if (!ReadMultiXactCounts(&multixacts, &members))
2826  return 0;
2827 
2828  /* If member space utilization is low, no special action is required. */
2829  if (members <= MULTIXACT_MEMBER_SAFE_THRESHOLD)
2831 
2832  /*
2833  * Compute a target for relminmxid advancement. The number of multixacts
2834  * we try to eliminate from the system is based on how far we are past
2835  * MULTIXACT_MEMBER_SAFE_THRESHOLD.
2836  */
2837  fraction = (double) (members - MULTIXACT_MEMBER_SAFE_THRESHOLD) /
2839  victim_multixacts = multixacts * fraction;
2840 
2841  /* fraction could be > 1.0, but lowest possible freeze age is zero */
2842  if (victim_multixacts > multixacts)
2843  return 0;
2844  return multixacts - victim_multixacts;
2845 }
2846 
2847 typedef struct mxtruncinfo
2848 {
2850 } mxtruncinfo;
2851 
2852 /*
2853  * SlruScanDirectory callback
2854  * This callback determines the earliest existing page number.
2855  */
2856 static bool
2857 SlruScanDirCbFindEarliest(SlruCtl ctl, char *filename, int segpage, void *data)
2858 {
2859  mxtruncinfo *trunc = (mxtruncinfo *) data;
2860 
2861  if (trunc->earliestExistingPage == -1 ||
2862  ctl->PagePrecedes(segpage, trunc->earliestExistingPage))
2863  {
2864  trunc->earliestExistingPage = segpage;
2865  }
2866 
2867  return false; /* keep going */
2868 }
2869 
2870 
2871 /*
2872  * Delete members segments [oldest, newOldest)
2873  *
2874  * The members SLRU can, in contrast to the offsets one, be filled to almost
2875  * the full range at once. This means SimpleLruTruncate() can't trivially be
2876  * used - instead the to-be-deleted range is computed using the offsets
2877  * SLRU. C.f. TruncateMultiXact().
2878  */
2879 static void
2881 {
2882  const int maxsegment = MXOffsetToMemberSegment(MaxMultiXactOffset);
2883  int startsegment = MXOffsetToMemberSegment(oldestOffset);
2884  int endsegment = MXOffsetToMemberSegment(newOldestOffset);
2885  int segment = startsegment;
2886 
2887  /*
2888  * Delete all the segments but the last one. The last segment can still
2889  * contain, possibly partially, valid data.
2890  */
2891  while (segment != endsegment)
2892  {
2893  elog(DEBUG2, "truncating multixact members segment %x", segment);
2895 
2896  /* move to next segment, handling wraparound correctly */
2897  if (segment == maxsegment)
2898  segment = 0;
2899  else
2900  segment += 1;
2901  }
2902 }
2903 
2904 /*
2905  * Delete offsets segments [oldest, newOldest)
2906  */
2907 static void
2909 {
2910  /*
2911  * We step back one multixact to avoid passing a cutoff page that hasn't
2912  * been created yet in the rare case that oldestMulti would be the first
2913  * item on a page and oldestMulti == nextMulti. In that case, if we
2914  * didn't subtract one, we'd trigger SimpleLruTruncate's wraparound
2915  * detection.
2916  */
2918  MultiXactIdToOffsetPage(PreviousMultiXactId(newOldestMulti)));
2919 }
2920 
2921 /*
2922  * Remove all MultiXactOffset and MultiXactMember segments before the oldest
2923  * ones still of interest.
2924  *
2925  * This is only called on a primary as part of vacuum (via
2926  * vac_truncate_clog()). During recovery truncation is done by replaying
2927  * truncation WAL records logged here.
2928  *
2929  * newOldestMulti is the oldest currently required multixact, newOldestMultiDB
2930  * is one of the databases preventing newOldestMulti from increasing.
2931  */
2932 void
2933 TruncateMultiXact(MultiXactId newOldestMulti, Oid newOldestMultiDB)
2934 {
2935  MultiXactId oldestMulti;
2936  MultiXactId nextMulti;
2937  MultiXactOffset newOldestOffset;
2938  MultiXactOffset oldestOffset;
2939  MultiXactOffset nextOffset;
2940  mxtruncinfo trunc;
2941  MultiXactId earliest;
2942 
2944  Assert(MultiXactState->finishedStartup);
2945 
2946  /*
2947  * We can only allow one truncation to happen at once. Otherwise parts of
2948  * members might vanish while we're doing lookups or similar. There's no
2949  * need to have an interlock with creating new multis or such, since those
2950  * are constrained by the limits (which only grow, never shrink).
2951  */
2952  LWLockAcquire(MultiXactTruncationLock, LW_EXCLUSIVE);
2953 
2954  LWLockAcquire(MultiXactGenLock, LW_SHARED);
2955  nextMulti = MultiXactState->nextMXact;
2956  nextOffset = MultiXactState->nextOffset;
2957  oldestMulti = MultiXactState->oldestMultiXactId;
2958  LWLockRelease(MultiXactGenLock);
2959  Assert(MultiXactIdIsValid(oldestMulti));
2960 
2961  /*
2962  * Make sure to only attempt truncation if there's values to truncate
2963  * away. In normal processing values shouldn't go backwards, but there's
2964  * some corner cases (due to bugs) where that's possible.
2965  */
2966  if (MultiXactIdPrecedesOrEquals(newOldestMulti, oldestMulti))
2967  {
2968  LWLockRelease(MultiXactTruncationLock);
2969  return;
2970  }
2971 
2972  /*
2973  * Note we can't just plow ahead with the truncation; it's possible that
2974  * there are no segments to truncate, which is a problem because we are
2975  * going to attempt to read the offsets page to determine where to
2976  * truncate the members SLRU. So we first scan the directory to determine
2977  * the earliest offsets page number that we can read without error.
2978  *
2979  * NB: It's also possible that the page that oldestMulti is on has already
2980  * been truncated away, and we crashed before updating oldestMulti.
2981  */
2982  trunc.earliestExistingPage = -1;
2985  if (earliest < FirstMultiXactId)
2986  earliest = FirstMultiXactId;
2987 
2988  /* If there's nothing to remove, we can bail out early. */
2989  if (MultiXactIdPrecedes(oldestMulti, earliest))
2990  {
2991  LWLockRelease(MultiXactTruncationLock);
2992  return;
2993  }
2994 
2995  /*
2996  * First, compute the safe truncation point for MultiXactMember. This is
2997  * the starting offset of the oldest multixact.
2998  *
2999  * Hopefully, find_multixact_start will always work here, because we've
3000  * already checked that it doesn't precede the earliest MultiXact on disk.
3001  * But if it fails, don't truncate anything, and log a message.
3002  */
3003  if (oldestMulti == nextMulti)
3004  {
3005  /* there are NO MultiXacts */
3006  oldestOffset = nextOffset;
3007  }
3008  else if (!find_multixact_start(oldestMulti, &oldestOffset))
3009  {
3010  ereport(LOG,
3011  (errmsg("oldest MultiXact %u not found, earliest MultiXact %u, skipping truncation",
3012  oldestMulti, earliest)));
3013  LWLockRelease(MultiXactTruncationLock);
3014  return;
3015  }
3016 
3017  /*
3018  * Secondly compute up to where to truncate. Lookup the corresponding
3019  * member offset for newOldestMulti for that.
3020  */
3021  if (newOldestMulti == nextMulti)
3022  {
3023  /* there are NO MultiXacts */
3024  newOldestOffset = nextOffset;
3025  }
3026  else if (!find_multixact_start(newOldestMulti, &newOldestOffset))
3027  {
3028  ereport(LOG,
3029  (errmsg("cannot truncate up to MultiXact %u because it does not exist on disk, skipping truncation",
3030  newOldestMulti)));
3031  LWLockRelease(MultiXactTruncationLock);
3032  return;
3033  }
3034 
3035  elog(DEBUG1, "performing multixact truncation: "
3036  "offsets [%u, %u), offsets segments [%x, %x), "
3037  "members [%u, %u), members segments [%x, %x)",
3038  oldestMulti, newOldestMulti,
3039  MultiXactIdToOffsetSegment(oldestMulti),
3040  MultiXactIdToOffsetSegment(newOldestMulti),
3041  oldestOffset, newOldestOffset,
3042  MXOffsetToMemberSegment(oldestOffset),
3043  MXOffsetToMemberSegment(newOldestOffset));
3044 
3045  /*
3046  * Do truncation, and the WAL logging of the truncation, in a critical
3047  * section. That way offsets/members cannot get out of sync anymore, i.e.
3048  * once consistent the newOldestMulti will always exist in members, even
3049  * if we crashed in the wrong moment.
3050  */
3052 
3053  /*
3054  * Prevent checkpoints from being scheduled concurrently. This is critical
3055  * because otherwise a truncation record might not be replayed after a
3056  * crash/basebackup, even though the state of the data directory would
3057  * require it.
3058  */
3060  MyPgXact->delayChkpt = true;
3061 
3062  /* WAL log truncation */
3063  WriteMTruncateXlogRec(newOldestMultiDB,
3064  oldestMulti, newOldestMulti,
3065  oldestOffset, newOldestOffset);
3066 
3067  /*
3068  * Update in-memory limits before performing the truncation, while inside
3069  * the critical section: Have to do it before truncation, to prevent
3070  * concurrent lookups of those values. Has to be inside the critical
3071  * section as otherwise a future call to this function would error out,
3072  * while looking up the oldest member in offsets, if our caller crashes
3073  * before updating the limits.
3074  */
3075  LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
3076  MultiXactState->oldestMultiXactId = newOldestMulti;
3077  MultiXactState->oldestMultiXactDB = newOldestMultiDB;
3078  LWLockRelease(MultiXactGenLock);
3079 
3080  /* First truncate members */
3081  PerformMembersTruncation(oldestOffset, newOldestOffset);
3082 
3083  /* Then offsets */
3084  PerformOffsetsTruncation(oldestMulti, newOldestMulti);
3085 
3086  MyPgXact->delayChkpt = false;
3087 
3088  END_CRIT_SECTION();
3089  LWLockRelease(MultiXactTruncationLock);
3090 }
3091 
3092 /*
3093  * Decide which of two MultiXactOffset page numbers is "older" for truncation
3094  * purposes.
3095  *
3096  * We need to use comparison of MultiXactId here in order to do the right
3097  * thing with wraparound. However, if we are asked about page number zero, we
3098  * don't want to hand InvalidMultiXactId to MultiXactIdPrecedes: it'll get
3099  * weird. So, offset both multis by FirstMultiXactId to avoid that.
3100  * (Actually, the current implementation doesn't do anything weird with
3101  * InvalidMultiXactId, but there's no harm in leaving this code like this.)
3102  */
3103 static bool
3104 MultiXactOffsetPagePrecedes(int page1, int page2)
3105 {
3106  MultiXactId multi1;
3107  MultiXactId multi2;
3108 
3109  multi1 = ((MultiXactId) page1) * MULTIXACT_OFFSETS_PER_PAGE;
3110  multi1 += FirstMultiXactId;
3111  multi2 = ((MultiXactId) page2) * MULTIXACT_OFFSETS_PER_PAGE;
3112  multi2 += FirstMultiXactId;
3113 
3114  return MultiXactIdPrecedes(multi1, multi2);
3115 }
3116 
3117 /*
3118  * Decide which of two MultiXactMember page numbers is "older" for truncation
3119  * purposes. There is no "invalid offset number" so use the numbers verbatim.
3120  */
3121 static bool
3122 MultiXactMemberPagePrecedes(int page1, int page2)
3123 {
3124  MultiXactOffset offset1;
3125  MultiXactOffset offset2;
3126 
3127  offset1 = ((MultiXactOffset) page1) * MULTIXACT_MEMBERS_PER_PAGE;
3128  offset2 = ((MultiXactOffset) page2) * MULTIXACT_MEMBERS_PER_PAGE;
3129 
3130  return MultiXactOffsetPrecedes(offset1, offset2);
3131 }
3132 
3133 /*
3134  * Decide which of two MultiXactIds is earlier.
3135  *
3136  * XXX do we need to do something special for InvalidMultiXactId?
3137  * (Doesn't look like it.)
3138  */
3139 bool
3141 {
3142  int32 diff = (int32) (multi1 - multi2);
3143 
3144  return (diff < 0);
3145 }
3146 
3147 /*
3148  * MultiXactIdPrecedesOrEquals -- is multi1 logically <= multi2?
3149  *
3150  * XXX do we need to do something special for InvalidMultiXactId?
3151  * (Doesn't look like it.)
3152  */
3153 bool
3155 {
3156  int32 diff = (int32) (multi1 - multi2);
3157 
3158  return (diff <= 0);
3159 }
3160 
3161 
3162 /*
3163  * Decide which of two offsets is earlier.
3164  */
3165 static bool
3167 {
3168  int32 diff = (int32) (offset1 - offset2);
3169 
3170  return (diff < 0);
3171 }
3172 
3173 /*
3174  * Write an xlog record reflecting the zeroing of either a MEMBERs or
3175  * OFFSETs page (info shows which)
3176  */
3177 static void
3178 WriteMZeroPageXlogRec(int pageno, uint8 info)
3179 {
3180  XLogBeginInsert();
3181  XLogRegisterData((char *) (&pageno), sizeof(int));
3182  (void) XLogInsert(RM_MULTIXACT_ID, info);
3183 }
3184 
3185 /*
3186  * Write a TRUNCATE xlog record
3187  *
3188  * We must flush the xlog record to disk before returning --- see notes in
3189  * TruncateCLOG().
3190  */
3191 static void
3193  MultiXactId startTruncOff, MultiXactId endTruncOff,
3194  MultiXactOffset startTruncMemb, MultiXactOffset endTruncMemb)
3195 {
3196  XLogRecPtr recptr;
3197  xl_multixact_truncate xlrec;
3198 
3199  xlrec.oldestMultiDB = oldestMultiDB;
3200 
3201  xlrec.startTruncOff = startTruncOff;
3202  xlrec.endTruncOff = endTruncOff;
3203 
3204  xlrec.startTruncMemb = startTruncMemb;
3205  xlrec.endTruncMemb = endTruncMemb;
3206 
3207  XLogBeginInsert();
3208  XLogRegisterData((char *) (&xlrec), SizeOfMultiXactTruncate);
3209  recptr = XLogInsert(RM_MULTIXACT_ID, XLOG_MULTIXACT_TRUNCATE_ID);
3210  XLogFlush(recptr);
3211 }
3212 
3213 /*
3214  * MULTIXACT resource manager's routines
3215  */
3216 void
3218 {
3219  uint8 info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
3220 
3221  /* Backup blocks are not used in multixact records */
3222  Assert(!XLogRecHasAnyBlockRefs(record));
3223 
3224  if (info == XLOG_MULTIXACT_ZERO_OFF_PAGE)
3225  {
3226  int pageno;
3227  int slotno;
3228 
3229  memcpy(&pageno, XLogRecGetData(record), sizeof(int));
3230 
3231  LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
3232 
3233  slotno = ZeroMultiXactOffsetPage(pageno, false);
3235  Assert(!MultiXactOffsetCtl->shared->page_dirty[slotno]);
3236 
3237  LWLockRelease(MultiXactOffsetControlLock);
3238  }
3239  else if (info == XLOG_MULTIXACT_ZERO_MEM_PAGE)
3240  {
3241  int pageno;
3242  int slotno;
3243 
3244  memcpy(&pageno, XLogRecGetData(record), sizeof(int));
3245 
3246  LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
3247 
3248  slotno = ZeroMultiXactMemberPage(pageno, false);
3250  Assert(!MultiXactMemberCtl->shared->page_dirty[slotno]);
3251 
3252  LWLockRelease(MultiXactMemberControlLock);
3253  }
3254  else if (info == XLOG_MULTIXACT_CREATE_ID)
3255  {
3256  xl_multixact_create *xlrec =
3257  (xl_multixact_create *) XLogRecGetData(record);
3258  TransactionId max_xid;
3259  int i;
3260 
3261  /* Store the data back into the SLRU files */
3262  RecordNewMultiXact(xlrec->mid, xlrec->moff, xlrec->nmembers,
3263  xlrec->members);
3264 
3265  /* Make sure nextMXact/nextOffset are beyond what this record has */
3266  MultiXactAdvanceNextMXact(xlrec->mid + 1,
3267  xlrec->moff + xlrec->nmembers);
3268 
3269  /*
3270  * Make sure nextXid is beyond any XID mentioned in the record. This
3271  * should be unnecessary, since any XID found here ought to have other
3272  * evidence in the XLOG, but let's be safe.
3273  */
3274  max_xid = XLogRecGetXid(record);
3275  for (i = 0; i < xlrec->nmembers; i++)
3276  {
3277  if (TransactionIdPrecedes(max_xid, xlrec->members[i].xid))
3278  max_xid = xlrec->members[i].xid;
3279  }
3280 
3281  /*
3282  * We don't expect anyone else to modify nextXid, hence startup
3283  * process doesn't need to hold a lock while checking this. We still
3284  * acquire the lock to modify it, though.
3285  */
3286  if (TransactionIdFollowsOrEquals(max_xid,
3288  {
3289  LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
3290  ShmemVariableCache->nextXid = max_xid;
3292  LWLockRelease(XidGenLock);
3293  }
3294  }
3295  else if (info == XLOG_MULTIXACT_TRUNCATE_ID)
3296  {
3297  xl_multixact_truncate xlrec;
3298  int pageno;
3299 
3300  memcpy(&xlrec, XLogRecGetData(record),
3302 
3303  elog(DEBUG1, "replaying multixact truncation: "
3304  "offsets [%u, %u), offsets segments [%x, %x), "
3305  "members [%u, %u), members segments [%x, %x)",
3306  xlrec.startTruncOff, xlrec.endTruncOff,
3309  xlrec.startTruncMemb, xlrec.endTruncMemb,
3312 
3313  /* should not be required, but more than cheap enough */
3314  LWLockAcquire(MultiXactTruncationLock, LW_EXCLUSIVE);
3315 
3316  /*
3317  * Advance the horizon values, so they're current at the end of
3318  * recovery.
3319  */
3320  SetMultiXactIdLimit(xlrec.endTruncOff, xlrec.oldestMultiDB, false);
3321 
3323 
3324  /*
3325  * During XLOG replay, latest_page_number isn't necessarily set up
3326  * yet; insert a suitable value to bypass the sanity test in
3327  * SimpleLruTruncate.
3328  */
3329  pageno = MultiXactIdToOffsetPage(xlrec.endTruncOff);
3330  MultiXactOffsetCtl->shared->latest_page_number = pageno;
3332 
3333  LWLockRelease(MultiXactTruncationLock);
3334  }
3335  else
3336  elog(PANIC, "multixact_redo: unknown op code %u", info);
3337 }
3338 
3339 Datum
3341 {
3342  typedef struct
3343  {
3344  MultiXactMember *members;
3345  int nmembers;
3346  int iter;
3347  } mxact;
3348  MultiXactId mxid = PG_GETARG_UINT32(0);
3349  mxact *multi;
3350  FuncCallContext *funccxt;
3351 
3352  if (mxid < FirstMultiXactId)
3353  ereport(ERROR,
3354  (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
3355  errmsg("invalid MultiXactId: %u", mxid)));
3356 
3357  if (SRF_IS_FIRSTCALL())
3358  {
3359  MemoryContext oldcxt;
3360  TupleDesc tupdesc;
3361 
3362  funccxt = SRF_FIRSTCALL_INIT();
3363  oldcxt = MemoryContextSwitchTo(funccxt->multi_call_memory_ctx);
3364 
3365  multi = palloc(sizeof(mxact));
3366  /* no need to allow for old values here */
3367  multi->nmembers = GetMultiXactIdMembers(mxid, &multi->members, false,
3368  false);
3369  multi->iter = 0;
3370 
3371  tupdesc = CreateTemplateTupleDesc(2, false);
3372  TupleDescInitEntry(tupdesc, (AttrNumber) 1, "xid",
3373  XIDOID, -1, 0);
3374  TupleDescInitEntry(tupdesc, (AttrNumber) 2, "mode",
3375  TEXTOID, -1, 0);
3376 
3377  funccxt->attinmeta = TupleDescGetAttInMetadata(tupdesc);
3378  funccxt->user_fctx = multi;
3379 
3380  MemoryContextSwitchTo(oldcxt);
3381  }
3382 
3383  funccxt = SRF_PERCALL_SETUP();
3384  multi = (mxact *) funccxt->user_fctx;
3385 
3386  while (multi->iter < multi->nmembers)
3387  {
3388  HeapTuple tuple;
3389  char *values[2];
3390 
3391  values[0] = psprintf("%u", multi->members[multi->iter].xid);
3392  values[1] = mxstatus_to_string(multi->members[multi->iter].status);
3393 
3394  tuple = BuildTupleFromCStrings(funccxt->attinmeta, values);
3395 
3396  multi->iter++;
3397  pfree(values[0]);
3398  SRF_RETURN_NEXT(funccxt, HeapTupleGetDatum(tuple));
3399  }
3400 
3401  if (multi->nmembers > 0)
3402  pfree(multi->members);
3403  pfree(multi);
3404 
3405  SRF_RETURN_DONE(funccxt);
3406 }
#define MaxMultiXactOffset
Definition: multixact.h:29
void TrimMultiXact(void)
Definition: multixact.c:2003
#define TransactionIdAdvance(dest)
Definition: transam.h:48
#define PG_GETARG_UINT32(n)
Definition: fmgr.h:235
Datum pg_get_multixact_members(PG_FUNCTION_ARGS)
Definition: multixact.c:3340
static SlruCtlData MultiXactMemberCtlData
Definition: multixact.c:188
int length(const List *list)
Definition: list.c:1271
MultiXactStatus
Definition: multixact.h:40
#define MULTIXACT_MEMBER_DANGER_THRESHOLD
Definition: multixact.c:178
MultiXactId nextMXact
Definition: multixact.c:203
#define DEBUG1
Definition: elog.h:25
void StartupMultiXact(void)
Definition: multixact.c:1980
int errhint(const char *fmt,...)
Definition: elog.c:987
BackendId MyBackendId
Definition: globals.c:72
void AtPrepare_MultiXact(void)
Definition: multixact.c:1691
MemoryContext TopTransactionContext
Definition: mcxt.c:48
#define MXOffsetToFlagsBitShift(xid)
Definition: multixact.c:167
#define NUM_MXACTMEMBER_BUFFERS
Definition: multixact.h:33
static bool SlruScanDirCbFindEarliest(SlruCtl ctl, char *filename, int segpage, void *data)
Definition: multixact.c:2857
uint32 MultiXactOffset
Definition: c.h:409
#define TransactionIdEquals(id1, id2)
Definition: transam.h:43
#define debug_elog4(a, b, c, d)
Definition: multixact.c:335
uint32 TransactionId
Definition: c.h:397
static void dlist_push_head(dlist_head *head, dlist_node *node)
Definition: ilist.h:300
bool TransactionIdIsCurrentTransactionId(TransactionId xid)
Definition: xact.c:773
#define MaxMultiXactId
Definition: multixact.h:25
static MultiXactId * OldestMemberMXactId
Definition: multixact.c:292
int errmsg_plural(const char *fmt_singular, const char *fmt_plural, unsigned long n,...)
Definition: elog.c:850
MultiXactMember members[FLEXIBLE_ARRAY_MEMBER]
Definition: multixact.c:318
static int ZeroMultiXactOffsetPage(int pageno, bool writeXlog)
Definition: multixact.c:1903
static dlist_node * dlist_tail_node(dlist_head *head)
Definition: ilist.h:466
#define TEXTOID
Definition: pg_type.h:324
MultiXactOffset nextOffset
Definition: multixact.c:206
bool TransactionIdIsInProgress(TransactionId xid)
Definition: procarray.c:995
#define SRF_IS_FIRSTCALL()
Definition: funcapi.h:285
MultiXactId perBackendXactIds[FLEXIBLE_ARRAY_MEMBER]
Definition: multixact.c:281
#define MAX_CACHE_ENTRIES
Definition: multixact.c:321
#define dlist_foreach(iter, lhead)
Definition: ilist.h:507
void multixact_redo(XLogReaderState *record)
Definition: multixact.c:3217
char * psprintf(const char *fmt,...)
Definition: psprintf.c:46
#define ALLOCSET_SMALL_SIZES
Definition: memutils.h:175
void SimpleLruTruncate(SlruCtl ctl, int cutoffPage)
Definition: slru.c:1165
bool InRecovery
Definition: xlog.c:192
static bool MultiXactOffsetPagePrecedes(int page1, int page2)
Definition: multixact.c:3104
#define MULTIXACT_MEMBERS_PER_PAGE
Definition: multixact.c:142
#define END_CRIT_SECTION()
Definition: miscadmin.h:132
void BootStrapMultiXact(void)
Definition: multixact.c:1866
MultiXactId MultiXactIdCreateFromMembers(int nmembers, MultiXactMember *members)
Definition: multixact.c:746
bool TransactionIdFollowsOrEquals(TransactionId id1, TransactionId id2)
Definition: transam.c:349
static MemoryContext MemoryContextSwitchTo(MemoryContext context)
Definition: palloc.h:109
unsigned char uint8
Definition: c.h:266
static bool find_multixact_start(MultiXactId multi, MultiXactOffset *result)
Definition: multixact.c:2719
#define PreviousMultiXactId(xid)
Definition: multixact.c:181
static MultiXactId GetNewMultiXactId(int nmembers, MultiXactOffset *offset)
Definition: multixact.c:935
#define XLOG_MULTIXACT_ZERO_MEM_PAGE
Definition: multixact.h:72
#define START_CRIT_SECTION()
Definition: miscadmin.h:130
int autovacuum_multixact_freeze_max_age
Definition: autovacuum.c:119
int errcode(int sqlerrcode)
Definition: elog.c:575
#define MemSet(start, val, len)
Definition: c.h:857
void MultiXactGetCheckptMulti(bool is_shutdown, MultiXactId *nextMulti, MultiXactOffset *nextMultiOffset, MultiXactId *oldestMulti, Oid *oldestMultiDB)
Definition: multixact.c:2118
return result
Definition: formatting.c:1618
#define MXOffsetToMemberPage(xid)
Definition: multixact.c:159
#define XIDOID
Definition: pg_type.h:336
bool TransactionIdDidCommit(TransactionId transactionId)
Definition: transam.c:125
static MultiXactId * OldestVisibleMXactId
Definition: multixact.c:293
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Definition: multixact.c:317
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Definition: elog.h:26
unsigned int Oid
Definition: postgres_ext.h:31
bool RecoveryInProgress(void)
Definition: xlog.c:7860
static void MaybeExtendOffsetSlru(void)
Definition: multixact.c:1947
#define MXOffsetToFlagsOffset(xid)
Definition: multixact.c:163
void MultiXactAdvanceNextMXact(MultiXactId minMulti, MultiXactOffset minMultiOffset)
Definition: multixact.c:2347
struct mXactCacheEnt mXactCacheEnt
#define PANIC
Definition: elog.h:53
Size SimpleLruShmemSize(int nslots, int nlsns)
Definition: slru.c:145
void SimpleLruFlush(SlruCtl ctl, bool allow_redirtied)
Definition: slru.c:1100
#define SRF_PERCALL_SETUP()
Definition: funcapi.h:289
void XLogFlush(XLogRecPtr record)
Definition: xlog.c:2754
bool IsBinaryUpgrade
Definition: globals.c:101
void RegisterTwoPhaseRecord(TwoPhaseRmgrId rmid, uint16 info, const void *data, uint32 len)
Definition: twophase.c:1120
signed int int32
Definition: c.h:256
#define SizeOfMultiXactTruncate
Definition: multixact.h:99
PGXACT * MyPgXact
Definition: proc.c:68
#define MultiXactIdToOffsetEntry(xid)
Definition: multixact.c:113
HeapTuple BuildTupleFromCStrings(AttInMetadata *attinmeta, char **values)
Definition: execTuples.c:1115
#define MultiXactIdToOffsetPage(xid)
Definition: multixact.c:111
void MultiXactIdSetOldestMember(void)
Definition: multixact.c:623
static MultiXactStateData * MultiXactState
Definition: multixact.c:291
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Definition: lwlock.c:1715
#define SRF_RETURN_NEXT(_funcctx, _result)
Definition: funcapi.h:291
MultiXactId oldestMultiXactId
Definition: multixact.c:216
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Definition: multixact.h:84
MultiXactMember members[FLEXIBLE_ARRAY_MEMBER]
Definition: multixact.h:81
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Definition: signal.c:53
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Definition: ilist.h:477
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Definition: c.h:267
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Definition: mcxt.c:950
static bool MultiXactOffsetWouldWrap(MultiXactOffset boundary, MultiXactOffset start, uint32 distance)
Definition: multixact.c:2671
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Definition: xlogreader.h:218
#define NUM_MXACTOFFSET_BUFFERS
Definition: multixact.h:32
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Definition: stringinfo.c:110
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Definition: multixact.c:1820
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Definition: multixact.c:2544
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Definition: elog.h:43
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Definition: multixact.c:337
#define XLOG_MULTIXACT_CREATE_ID
Definition: multixact.h:73
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Definition: multixact.h:61
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Definition: multixact.c:228
#define MXOffsetToMemberOffset(xid)
Definition: multixact.c:172
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Definition: shmem.c:372
#define MXACT_MEMBER_XACT_BITMASK
Definition: multixact.c:132
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Definition: transam.h:117
int SimpleLruReadPage(SlruCtl ctl, int pageno, bool write_ok, TransactionId xid)
Definition: slru.c:371
static int MXactCacheMembers
Definition: multixact.c:323
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Definition: multixact.h:79
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Definition: dbcommands.c:2048
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Definition: elog.h:24
static void WriteMZeroPageXlogRec(int pageno, uint8 info)
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Definition: pg_test_fsync.c:65
#define MultiXactIdToOffsetSegment(xid)
Definition: multixact.c:115
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Definition: globals.c:100
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Definition: funcapi.h:99
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Definition: multixact.h:62
BackendId TwoPhaseGetDummyBackendId(TransactionId xid)
Definition: twophase.c:812
static void WriteMTruncateXlogRec(Oid oldestMultiDB, MultiXactId startOff, MultiXactId endOff, MultiXactOffset startMemb, MultiXactOffset endMemb)
Definition: multixact.c:3192
static void PerformMembersTruncation(MultiXactOffset oldestOffset, MultiXactOffset newOldestOffset)
Definition: multixact.c:2880
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Definition: varsup.c:34
void multixact_twophase_postcommit(TransactionId xid, uint16 info, void *recdata, uint32 len)
Definition: multixact.c:1776
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Definition: multixact.c:230
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#define ISUPDATE_from_mxstatus(status)
Definition: multixact.h:55
unsigned int uint32
Definition: c.h:268
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Definition: multixact.c:2105
#define MultiXactIdIsValid(multi)
Definition: multixact.h:27
bool SimpleLruDoesPhysicalPageExist(SlruCtl ctl, int pageno)
Definition: slru.c:586
#define debug_elog2(a, b)
Definition: multixact.c:333
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Definition: slru.c:574
#define FirstMultiXactId
Definition: multixact.h:24
static void dlist_delete(dlist_node *node)
Definition: ilist.h:358
char * mxid_to_string(MultiXactId multi, int nmembers, MultiXactMember *members)
Definition: multixact.c:1631
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Definition: tupdesc.c:493
#define TWOPHASE_RM_MULTIXACT_ID
Definition: twophase_rmgr.h:27
#define ereport(elevel, rest)
Definition: elog.h:122
#define MULTIXACT_OFFSETS_PER_PAGE
Definition: multixact.c:109
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Definition: multixact.c:2817
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Definition: c.h:677
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Definition: proc.h:220
#define XLogRecGetInfo(decoder)
Definition: xlogreader.h:214
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Definition: mcxt.c:43
bool TransactionIdPrecedes(TransactionId id1, TransactionId id2)
Definition: transam.c:300
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Definition: multixact.h:96
static bool MultiXactMemberPagePrecedes(int page1, int page2)
Definition: multixact.c:3122
#define MultiXactOffsetCtl
Definition: multixact.c:190
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Definition: stringinfo.c:201
void initStringInfo(StringInfo str)
Definition: stringinfo.c:65
#define DLIST_STATIC_INIT(name)
Definition: ilist.h:248
#define WARNING
Definition: elog.h:40
MultiXactOffset offsetStopLimit
Definition: multixact.c:234
MultiXactId MultiXactIdCreate(TransactionId xid1, MultiXactStatus status1, TransactionId xid2, MultiXactStatus status2)
Definition: multixact.c:384
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Definition: multixact.c:2140
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Definition: xloginsert.c:323
XLogRecPtr XLogInsert(RmgrId rmid, uint8 info)
Definition: xloginsert.c:415
#define XLogRecGetXid(decoder)
Definition: xlogreader.h:216
MultiXactId GetOldestMultiXactId(void)
Definition: multixact.c:2491
MemoryContext AllocSetContextCreate(MemoryContext parent, const char *name, Size minContextSize, Size initBlockSize, Size maxBlockSize)
Definition: aset.c:322
#define XLOG_MULTIXACT_ZERO_OFF_PAGE
Definition: multixact.h:71
uintptr_t Datum
Definition: postgres.h:372
MultiXactOffset oldestOffset
Definition: multixact.c:224
Datum difference(PG_FUNCTION_ARGS)
#define debug_elog3(a, b, c)
Definition: multixact.c:334
Size add_size(Size s1, Size s2)
Definition: shmem.c:475
int BackendId
Definition: backendid.h:21
#define OFFSET_WARN_SEGMENTS
AttInMetadata * TupleDescGetAttInMetadata(TupleDesc tupdesc)
Definition: execTuples.c:1068
bool(* PagePrecedes)(int, int)
Definition: slru.h:132
static void ExtendMultiXactOffset(MultiXactId multi)
Definition: multixact.c:2389
int SimpleLruReadPage_ReadOnly(SlruCtl ctl, int pageno, TransactionId xid)
Definition: slru.c:463
#define InvalidMultiXactId
Definition: multixact.h:23
dlist_node * cur
Definition: ilist.h:161
MultiXactOffset startTruncMemb
Definition: multixact.h:95
void SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid, bool is_startup)
Definition: multixact.c:2194
static void dlist_init(dlist_head *head)
Definition: ilist.h:278
static bool ReadMultiXactCounts(uint32 *multixacts, MultiXactOffset *members)
Definition: multixact.c:2761
TransactionId MultiXactId
Definition: c.h:407
MultiXactId multiWrapLimit
Definition: multixact.c:231
static SlruCtlData MultiXactOffsetCtlData
Definition: multixact.c:187
MultiXactId mid
Definition: multixact.h:78
#define NULL
Definition: c.h:229
uint64 XLogRecPtr
Definition: xlogdefs.h:21
#define Assert(condition)
Definition: c.h:675
#define XLR_INFO_MASK
Definition: xlogrecord.h:62
bool SlruScanDirectory(SlruCtl ctl, SlruScanCallback callback, void *data)
Definition: slru.c:1373
static dlist_head MXactCache
Definition: multixact.c:322
static void MultiXactIdSetOldestVisible(void)
Definition: multixact.c:680
#define XLOG_MULTIXACT_TRUNCATE_ID
Definition: multixact.h:74
MemoryContext multi_call_memory_ctx
Definition: funcapi.h:109
struct MultiXactMember MultiXactMember
size_t Size
Definition: c.h:356
#define MXOffsetToMemberSegment(xid)
Definition: multixact.c:160
int errdetail_plural(const char *fmt_singular, const char *fmt_plural, unsigned long n,...)
Definition: elog.c:965
void AtEOXact_MultiXact(void)
Definition: multixact.c:1662
void PostPrepare_MultiXact(TransactionId xid)
Definition: multixact.c:1705
MultiXactId startTruncOff
Definition: multixact.h:91
bool LWLockAcquire(LWLock *lock, LWLockMode mode)
Definition: lwlock.c:1111
bool IsTransactionState(void)
Definition: xact.c:350
static void mXactCachePut(MultiXactId multi, int nmembers, MultiXactMember *members)
Definition: multixact.c:1561
bool MultiXactIdPrecedes(MultiXactId multi1, MultiXactId multi2)
Definition: multixact.c:3140
MultiXactId multiWarnLimit
Definition: multixact.c:229
#define HeapTupleGetDatum(tuple)
Definition: funcapi.h:222
TupleDesc CreateTemplateTupleDesc(int natts, bool hasoid)
Definition: tupdesc.c:41
Size MultiXactShmemSize(void)
Definition: multixact.c:1803
void multixact_twophase_recover(TransactionId xid, uint16 info, void *recdata, uint32 len)
Definition: multixact.c:1755
static void dlist_move_head(dlist_head *head, dlist_node *node)
Definition: ilist.h:385
#define MXACT_MEMBER_BITS_PER_XACT
Definition: multixact.c:130
static Datum values[MAXATTR]
Definition: bootstrap.c:162
static char * filename
Definition: pg_dumpall.c:87
void * user_fctx
Definition: funcapi.h:90
void * palloc(Size size)
Definition: mcxt.c:849
int errmsg(const char *fmt,...)
Definition: elog.c:797
char * MemoryContextStrdup(MemoryContext context, const char *string)
Definition: mcxt.c:1064
static int ZeroMultiXactMemberPage(int pageno, bool writeXlog)
Definition: multixact.c:1919
void * MemoryContextAlloc(MemoryContext context, Size size)
Definition: mcxt.c:707
static int mXactCacheGetById(MultiXactId multi, MultiXactMember **members)
Definition: multixact.c:1515
static int mxactMemberComparator(const void *arg1, const void *arg2)
Definition: multixact.c:1443
bool MultiXactIdPrecedesOrEquals(MultiXactId multi1, MultiXactId multi2)
Definition: multixact.c:3154
int i
static char * mxstatus_to_string(MultiXactStatus status)
Definition: multixact.c:1608
static MemoryContext MXactContext
Definition: multixact.c:324
int earliestExistingPage
Definition: multixact.c:2849
#define MaxOldestSlot
Definition: multixact.c:288
#define XLogRecHasAnyBlockRefs(decoder)
Definition: xlogreader.h:220
#define PG_FUNCTION_ARGS
Definition: fmgr.h:158
void SlruDeleteSegment(SlruCtl ctl, int segno)
Definition: slru.c:1258
#define CHECK_FOR_INTERRUPTS()
Definition: miscadmin.h:97
#define MAX_MEMBERS_IN_LAST_MEMBERS_PAGE
Definition: multixact.c:155
void SendPostmasterSignal(PMSignalReason reason)
Definition: pmsignal.c:113
int GetMultiXactIdMembers(MultiXactId multi, MultiXactMember **members, bool from_pgupgrade, bool onlyLock)
Definition: multixact.c:1202
#define elog
Definition: elog.h:219
#define SLRU_PAGES_PER_SEGMENT
Definition: slru.h:37
static void RecordNewMultiXact(MultiXactId multi, MultiXactOffset offset, int nmembers, MultiXactMember *members)
Definition: multixact.c:841
struct MultiXactStateData MultiXactStateData
#define qsort(a, b, c, d)
Definition: port.h:440
#define TransactionIdIsValid(xid)
Definition: transam.h:41
MultiXactId endTruncOff
Definition: multixact.h:92
static void PerformOffsetsTruncation(MultiXactId oldestMulti, MultiXactId newOldestMulti)
Definition: multixact.c:2908
static void static void status(const char *fmt,...) pg_attribute_printf(1
Definition: pg_regress.c:224
#define MULTIXACT_MEMBER_SAFE_THRESHOLD
Definition: multixact.c:177
void TruncateMultiXact(MultiXactId newOldestMulti, Oid newOldestMultiDB)
Definition: multixact.c:2933
void XLogBeginInsert(void)
Definition: xloginsert.c:120
#define MultiXactMemberCtl
Definition: multixact.c:191
#define SHARED_MULTIXACT_STATE_SIZE
#define debug_elog5(a, b, c, d, e)
Definition: multixact.c:336
int16 AttrNumber
Definition: attnum.h:21
bool MultiXactIdIsRunning(MultiXactId multi, bool isLockOnly)
Definition: multixact.c:549
static bool MultiXactOffsetPrecedes(MultiXactOffset offset1, MultiXactOffset offset2)
Definition: multixact.c:3166
int SimpleLruZeroPage(SlruCtl ctl, int pageno)
Definition: slru.c:259
void MultiXactAdvanceOldest(MultiXactId oldestMulti, Oid oldestMultiDB)
Definition: multixact.c:2372
static MultiXactId mXactCacheGetBySet(int nmembers, MultiXactMember *members)
Definition: multixact.c:1473
static void ExtendMultiXactMember(MultiXactOffset offset, int nmembers)
Definition: multixact.c:2419
MultiXactId multi
Definition: multixact.c:315
#define offsetof(type, field)
Definition: c.h:555
MultiXactId MultiXactIdExpand(MultiXactId multi, TransactionId xid, MultiXactStatus status)
Definition: multixact.c:437
#define SRF_RETURN_DONE(_funcctx)
Definition: funcapi.h:309
MultiXactId ReadNextMultiXactId(void)
Definition: multixact.c:721
void MultiXactSetNextMXact(MultiXactId nextMulti, MultiXactOffset nextMultiOffset)
Definition: multixact.c:2160
void SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns, LWLock *ctllock, const char *subdir, int tranche_id)
Definition: slru.c:165
#define SRF_FIRSTCALL_INIT()
Definition: funcapi.h:287