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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) 1996-2021, 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/xloginsert.h"
78 #include "access/xlogutils.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 MultiXactOffsetSLRULock and
196  * MultiXactMemberSLRULock 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  */
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;
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);
367 static bool find_multixact_start(MultiXactId multi, MultiXactOffset *result);
368 static void WriteMZeroPageXlogRec(int pageno, uint8 info);
369 static void WriteMTruncateXlogRec(Oid oldestMultiDB,
370  MultiXactId startTruncOff,
371  MultiXactId endTruncOff,
372  MultiXactOffset startTruncMemb,
373  MultiXactOffset endTruncMemb);
374 
375 
376 /*
377  * MultiXactIdCreate
378  * Construct a MultiXactId representing two TransactionIds.
379  *
380  * The two XIDs must be different, or be requesting different statuses.
381  *
382  * NB - we don't worry about our local MultiXactId cache here, because that
383  * is handled by the lower-level routines.
384  */
387  TransactionId xid2, MultiXactStatus status2)
388 {
389  MultiXactId newMulti;
390  MultiXactMember members[2];
391 
394 
395  Assert(!TransactionIdEquals(xid1, xid2) || (status1 != status2));
396 
397  /* MultiXactIdSetOldestMember() must have been called already. */
399 
400  /*
401  * Note: unlike MultiXactIdExpand, we don't bother to check that both XIDs
402  * are still running. In typical usage, xid2 will be our own XID and the
403  * caller just did a check on xid1, so it'd be wasted effort.
404  */
405 
406  members[0].xid = xid1;
407  members[0].status = status1;
408  members[1].xid = xid2;
409  members[1].status = status2;
410 
411  newMulti = MultiXactIdCreateFromMembers(2, members);
412 
413  debug_elog3(DEBUG2, "Create: %s",
414  mxid_to_string(newMulti, 2, members));
415 
416  return newMulti;
417 }
418 
419 /*
420  * MultiXactIdExpand
421  * Add a TransactionId to a pre-existing MultiXactId.
422  *
423  * If the TransactionId is already a member of the passed MultiXactId with the
424  * same status, just return it as-is.
425  *
426  * Note that we do NOT actually modify the membership of a pre-existing
427  * MultiXactId; instead we create a new one. This is necessary to avoid
428  * a race condition against code trying to wait for one MultiXactId to finish;
429  * see notes in heapam.c.
430  *
431  * NB - we don't worry about our local MultiXactId cache here, because that
432  * is handled by the lower-level routines.
433  *
434  * Note: It is critical that MultiXactIds that come from an old cluster (i.e.
435  * one upgraded by pg_upgrade from a cluster older than this feature) are not
436  * passed in.
437  */
440 {
441  MultiXactId newMulti;
442  MultiXactMember *members;
443  MultiXactMember *newMembers;
444  int nmembers;
445  int i;
446  int j;
447 
450 
451  /* MultiXactIdSetOldestMember() must have been called already. */
453 
454  debug_elog5(DEBUG2, "Expand: received multi %u, xid %u status %s",
455  multi, xid, mxstatus_to_string(status));
456 
457  /*
458  * Note: we don't allow for old multis here. The reason is that the only
459  * caller of this function does a check that the multixact is no longer
460  * running.
461  */
462  nmembers = GetMultiXactIdMembers(multi, &members, false, false);
463 
464  if (nmembers < 0)
465  {
466  MultiXactMember member;
467 
468  /*
469  * The MultiXactId is obsolete. This can only happen if all the
470  * MultiXactId members stop running between the caller checking and
471  * passing it to us. It would be better to return that fact to the
472  * caller, but it would complicate the API and it's unlikely to happen
473  * too often, so just deal with it by creating a singleton MultiXact.
474  */
475  member.xid = xid;
476  member.status = status;
477  newMulti = MultiXactIdCreateFromMembers(1, &member);
478 
479  debug_elog4(DEBUG2, "Expand: %u has no members, create singleton %u",
480  multi, newMulti);
481  return newMulti;
482  }
483 
484  /*
485  * If the TransactionId is already a member of the MultiXactId with the
486  * same status, just return the existing MultiXactId.
487  */
488  for (i = 0; i < nmembers; i++)
489  {
490  if (TransactionIdEquals(members[i].xid, xid) &&
491  (members[i].status == status))
492  {
493  debug_elog4(DEBUG2, "Expand: %u is already a member of %u",
494  xid, multi);
495  pfree(members);
496  return multi;
497  }
498  }
499 
500  /*
501  * Determine which of the members of the MultiXactId are still of
502  * interest. This is any running transaction, and also any transaction
503  * that grabbed something stronger than just a lock and was committed. (An
504  * update that aborted is of no interest here; and having more than one
505  * update Xid in a multixact would cause errors elsewhere.)
506  *
507  * Removing dead members is not just an optimization: freezing of tuples
508  * whose Xmax are multis depends on this behavior.
509  *
510  * Note we have the same race condition here as above: j could be 0 at the
511  * end of the loop.
512  */
513  newMembers = (MultiXactMember *)
514  palloc(sizeof(MultiXactMember) * (nmembers + 1));
515 
516  for (i = 0, j = 0; i < nmembers; i++)
517  {
518  if (TransactionIdIsInProgress(members[i].xid) ||
519  (ISUPDATE_from_mxstatus(members[i].status) &&
520  TransactionIdDidCommit(members[i].xid)))
521  {
522  newMembers[j].xid = members[i].xid;
523  newMembers[j++].status = members[i].status;
524  }
525  }
526 
527  newMembers[j].xid = xid;
528  newMembers[j++].status = status;
529  newMulti = MultiXactIdCreateFromMembers(j, newMembers);
530 
531  pfree(members);
532  pfree(newMembers);
533 
534  debug_elog3(DEBUG2, "Expand: returning new multi %u", newMulti);
535 
536  return newMulti;
537 }
538 
539 /*
540  * MultiXactIdIsRunning
541  * Returns whether a MultiXactId is "running".
542  *
543  * We return true if at least one member of the given MultiXactId is still
544  * running. Note that a "false" result is certain not to change,
545  * because it is not legal to add members to an existing MultiXactId.
546  *
547  * Caller is expected to have verified that the multixact does not come from
548  * a pg_upgraded share-locked tuple.
549  */
550 bool
551 MultiXactIdIsRunning(MultiXactId multi, bool isLockOnly)
552 {
553  MultiXactMember *members;
554  int nmembers;
555  int i;
556 
557  debug_elog3(DEBUG2, "IsRunning %u?", multi);
558 
559  /*
560  * "false" here means we assume our callers have checked that the given
561  * multi cannot possibly come from a pg_upgraded database.
562  */
563  nmembers = GetMultiXactIdMembers(multi, &members, false, isLockOnly);
564 
565  if (nmembers <= 0)
566  {
567  debug_elog2(DEBUG2, "IsRunning: no members");
568  return false;
569  }
570 
571  /*
572  * Checking for myself is cheap compared to looking in shared memory;
573  * return true if any live subtransaction of the current top-level
574  * transaction is a member.
575  *
576  * This is not needed for correctness, it's just a fast path.
577  */
578  for (i = 0; i < nmembers; i++)
579  {
580  if (TransactionIdIsCurrentTransactionId(members[i].xid))
581  {
582  debug_elog3(DEBUG2, "IsRunning: I (%d) am running!", i);
583  pfree(members);
584  return true;
585  }
586  }
587 
588  /*
589  * This could be made faster by having another entry point in procarray.c,
590  * walking the PGPROC array only once for all the members. But in most
591  * cases nmembers should be small enough that it doesn't much matter.
592  */
593  for (i = 0; i < nmembers; i++)
594  {
595  if (TransactionIdIsInProgress(members[i].xid))
596  {
597  debug_elog4(DEBUG2, "IsRunning: member %d (%u) is running",
598  i, members[i].xid);
599  pfree(members);
600  return true;
601  }
602  }
603 
604  pfree(members);
605 
606  debug_elog3(DEBUG2, "IsRunning: %u is not running", multi);
607 
608  return false;
609 }
610 
611 /*
612  * MultiXactIdSetOldestMember
613  * Save the oldest MultiXactId this transaction could be a member of.
614  *
615  * We set the OldestMemberMXactId for a given transaction the first time it's
616  * going to do some operation that might require a MultiXactId (tuple lock,
617  * update or delete). We need to do this even if we end up using a
618  * TransactionId instead of a MultiXactId, because there is a chance that
619  * another transaction would add our XID to a MultiXactId.
620  *
621  * The value to set is the next-to-be-assigned MultiXactId, so this is meant to
622  * be called just before doing any such possibly-MultiXactId-able operation.
623  */
624 void
626 {
628  {
630 
631  /*
632  * You might think we don't need to acquire a lock here, since
633  * fetching and storing of TransactionIds is probably atomic, but in
634  * fact we do: suppose we pick up nextMXact and then lose the CPU for
635  * a long time. Someone else could advance nextMXact, and then
636  * another someone else could compute an OldestVisibleMXactId that
637  * would be after the value we are going to store when we get control
638  * back. Which would be wrong.
639  *
640  * Note that a shared lock is sufficient, because it's enough to stop
641  * someone from advancing nextMXact; and nobody else could be trying
642  * to write to our OldestMember entry, only reading (and we assume
643  * storing it is atomic.)
644  */
645  LWLockAcquire(MultiXactGenLock, LW_SHARED);
646 
647  /*
648  * We have to beware of the possibility that nextMXact is in the
649  * wrapped-around state. We don't fix the counter itself here, but we
650  * must be sure to store a valid value in our array entry.
651  */
652  nextMXact = MultiXactState->nextMXact;
653  if (nextMXact < FirstMultiXactId)
654  nextMXact = FirstMultiXactId;
655 
657 
658  LWLockRelease(MultiXactGenLock);
659 
660  debug_elog4(DEBUG2, "MultiXact: setting OldestMember[%d] = %u",
661  MyBackendId, nextMXact);
662  }
663 }
664 
665 /*
666  * MultiXactIdSetOldestVisible
667  * Save the oldest MultiXactId this transaction considers possibly live.
668  *
669  * We set the OldestVisibleMXactId for a given transaction the first time
670  * it's going to inspect any MultiXactId. Once we have set this, we are
671  * guaranteed that the checkpointer won't truncate off SLRU data for
672  * MultiXactIds at or after our OldestVisibleMXactId.
673  *
674  * The value to set is the oldest of nextMXact and all the valid per-backend
675  * OldestMemberMXactId[] entries. Because of the locking we do, we can be
676  * certain that no subsequent call to MultiXactIdSetOldestMember can set
677  * an OldestMemberMXactId[] entry older than what we compute here. Therefore
678  * there is no live transaction, now or later, that can be a member of any
679  * MultiXactId older than the OldestVisibleMXactId we compute here.
680  */
681 static void
683 {
685  {
686  MultiXactId oldestMXact;
687  int i;
688 
689  LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
690 
691  /*
692  * We have to beware of the possibility that nextMXact is in the
693  * wrapped-around state. We don't fix the counter itself here, but we
694  * must be sure to store a valid value in our array entry.
695  */
696  oldestMXact = MultiXactState->nextMXact;
697  if (oldestMXact < FirstMultiXactId)
698  oldestMXact = FirstMultiXactId;
699 
700  for (i = 1; i <= MaxOldestSlot; i++)
701  {
702  MultiXactId thisoldest = OldestMemberMXactId[i];
703 
704  if (MultiXactIdIsValid(thisoldest) &&
705  MultiXactIdPrecedes(thisoldest, oldestMXact))
706  oldestMXact = thisoldest;
707  }
708 
709  OldestVisibleMXactId[MyBackendId] = oldestMXact;
710 
711  LWLockRelease(MultiXactGenLock);
712 
713  debug_elog4(DEBUG2, "MultiXact: setting OldestVisible[%d] = %u",
714  MyBackendId, oldestMXact);
715  }
716 }
717 
718 /*
719  * ReadNextMultiXactId
720  * Return the next MultiXactId to be assigned, but don't allocate it
721  */
724 {
725  MultiXactId mxid;
726 
727  /* XXX we could presumably do this without a lock. */
728  LWLockAcquire(MultiXactGenLock, LW_SHARED);
729  mxid = MultiXactState->nextMXact;
730  LWLockRelease(MultiXactGenLock);
731 
732  if (mxid < FirstMultiXactId)
733  mxid = FirstMultiXactId;
734 
735  return mxid;
736 }
737 
738 /*
739  * ReadMultiXactIdRange
740  * Get the range of IDs that may still be referenced by a relation.
741  */
742 void
744 {
745  LWLockAcquire(MultiXactGenLock, LW_SHARED);
746  *oldest = MultiXactState->oldestMultiXactId;
747  *next = MultiXactState->nextMXact;
748  LWLockRelease(MultiXactGenLock);
749 
750  if (*oldest < FirstMultiXactId)
751  *oldest = FirstMultiXactId;
752  if (*next < FirstMultiXactId)
753  *next = FirstMultiXactId;
754 }
755 
756 
757 /*
758  * MultiXactIdCreateFromMembers
759  * Make a new MultiXactId from the specified set of members
760  *
761  * Make XLOG, SLRU and cache entries for a new MultiXactId, recording the
762  * given TransactionIds as members. Returns the newly created MultiXactId.
763  *
764  * NB: the passed members[] array will be sorted in-place.
765  */
768 {
769  MultiXactId multi;
770  MultiXactOffset offset;
771  xl_multixact_create xlrec;
772 
773  debug_elog3(DEBUG2, "Create: %s",
774  mxid_to_string(InvalidMultiXactId, nmembers, members));
775 
776  /*
777  * See if the same set of members already exists in our cache; if so, just
778  * re-use that MultiXactId. (Note: it might seem that looking in our
779  * cache is insufficient, and we ought to search disk to see if a
780  * duplicate definition already exists. But since we only ever create
781  * MultiXacts containing our own XID, in most cases any such MultiXacts
782  * were in fact created by us, and so will be in our cache. There are
783  * corner cases where someone else added us to a MultiXact without our
784  * knowledge, but it's not worth checking for.)
785  */
786  multi = mXactCacheGetBySet(nmembers, members);
787  if (MultiXactIdIsValid(multi))
788  {
789  debug_elog2(DEBUG2, "Create: in cache!");
790  return multi;
791  }
792 
793  /* Verify that there is a single update Xid among the given members. */
794  {
795  int i;
796  bool has_update = false;
797 
798  for (i = 0; i < nmembers; i++)
799  {
800  if (ISUPDATE_from_mxstatus(members[i].status))
801  {
802  if (has_update)
803  elog(ERROR, "new multixact has more than one updating member");
804  has_update = true;
805  }
806  }
807  }
808 
809  /*
810  * Assign the MXID and offsets range to use, and make sure there is space
811  * in the OFFSETs and MEMBERs files. NB: this routine does
812  * START_CRIT_SECTION().
813  *
814  * Note: unlike MultiXactIdCreate and MultiXactIdExpand, we do not check
815  * that we've called MultiXactIdSetOldestMember here. This is because
816  * this routine is used in some places to create new MultiXactIds of which
817  * the current backend is not a member, notably during freezing of multis
818  * in vacuum. During vacuum, in particular, it would be unacceptable to
819  * keep OldestMulti set, in case it runs for long.
820  */
821  multi = GetNewMultiXactId(nmembers, &offset);
822 
823  /* Make an XLOG entry describing the new MXID. */
824  xlrec.mid = multi;
825  xlrec.moff = offset;
826  xlrec.nmembers = nmembers;
827 
828  /*
829  * XXX Note: there's a lot of padding space in MultiXactMember. We could
830  * find a more compact representation of this Xlog record -- perhaps all
831  * the status flags in one XLogRecData, then all the xids in another one?
832  * Not clear that it's worth the trouble though.
833  */
834  XLogBeginInsert();
835  XLogRegisterData((char *) (&xlrec), SizeOfMultiXactCreate);
836  XLogRegisterData((char *) members, nmembers * sizeof(MultiXactMember));
837 
838  (void) XLogInsert(RM_MULTIXACT_ID, XLOG_MULTIXACT_CREATE_ID);
839 
840  /* Now enter the information into the OFFSETs and MEMBERs logs */
841  RecordNewMultiXact(multi, offset, nmembers, members);
842 
843  /* Done with critical section */
845 
846  /* Store the new MultiXactId in the local cache, too */
847  mXactCachePut(multi, nmembers, members);
848 
849  debug_elog2(DEBUG2, "Create: all done");
850 
851  return multi;
852 }
853 
854 /*
855  * RecordNewMultiXact
856  * Write info about a new multixact into the offsets and members files
857  *
858  * This is broken out of MultiXactIdCreateFromMembers so that xlog replay can
859  * use it.
860  */
861 static void
863  int nmembers, MultiXactMember *members)
864 {
865  int pageno;
866  int prev_pageno;
867  int entryno;
868  int slotno;
869  MultiXactOffset *offptr;
870  int i;
871 
872  LWLockAcquire(MultiXactOffsetSLRULock, LW_EXCLUSIVE);
873 
874  pageno = MultiXactIdToOffsetPage(multi);
875  entryno = MultiXactIdToOffsetEntry(multi);
876 
877  /*
878  * Note: we pass the MultiXactId to SimpleLruReadPage as the "transaction"
879  * to complain about if there's any I/O error. This is kinda bogus, but
880  * since the errors will always give the full pathname, it should be clear
881  * enough that a MultiXactId is really involved. Perhaps someday we'll
882  * take the trouble to generalize the slru.c error reporting code.
883  */
884  slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, multi);
885  offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
886  offptr += entryno;
887 
888  *offptr = offset;
889 
890  MultiXactOffsetCtl->shared->page_dirty[slotno] = true;
891 
892  /* Exchange our lock */
893  LWLockRelease(MultiXactOffsetSLRULock);
894 
895  LWLockAcquire(MultiXactMemberSLRULock, LW_EXCLUSIVE);
896 
897  prev_pageno = -1;
898 
899  for (i = 0; i < nmembers; i++, offset++)
900  {
901  TransactionId *memberptr;
902  uint32 *flagsptr;
903  uint32 flagsval;
904  int bshift;
905  int flagsoff;
906  int memberoff;
907 
908  Assert(members[i].status <= MultiXactStatusUpdate);
909 
910  pageno = MXOffsetToMemberPage(offset);
911  memberoff = MXOffsetToMemberOffset(offset);
912  flagsoff = MXOffsetToFlagsOffset(offset);
913  bshift = MXOffsetToFlagsBitShift(offset);
914 
915  if (pageno != prev_pageno)
916  {
917  slotno = SimpleLruReadPage(MultiXactMemberCtl, pageno, true, multi);
918  prev_pageno = pageno;
919  }
920 
921  memberptr = (TransactionId *)
922  (MultiXactMemberCtl->shared->page_buffer[slotno] + memberoff);
923 
924  *memberptr = members[i].xid;
925 
926  flagsptr = (uint32 *)
927  (MultiXactMemberCtl->shared->page_buffer[slotno] + flagsoff);
928 
929  flagsval = *flagsptr;
930  flagsval &= ~(((1 << MXACT_MEMBER_BITS_PER_XACT) - 1) << bshift);
931  flagsval |= (members[i].status << bshift);
932  *flagsptr = flagsval;
933 
934  MultiXactMemberCtl->shared->page_dirty[slotno] = true;
935  }
936 
937  LWLockRelease(MultiXactMemberSLRULock);
938 }
939 
940 /*
941  * GetNewMultiXactId
942  * Get the next MultiXactId.
943  *
944  * Also, reserve the needed amount of space in the "members" area. The
945  * starting offset of the reserved space is returned in *offset.
946  *
947  * This may generate XLOG records for expansion of the offsets and/or members
948  * files. Unfortunately, we have to do that while holding MultiXactGenLock
949  * to avoid race conditions --- the XLOG record for zeroing a page must appear
950  * before any backend can possibly try to store data in that page!
951  *
952  * We start a critical section before advancing the shared counters. The
953  * caller must end the critical section after writing SLRU data.
954  */
955 static MultiXactId
956 GetNewMultiXactId(int nmembers, MultiXactOffset *offset)
957 {
958  MultiXactId result;
960 
961  debug_elog3(DEBUG2, "GetNew: for %d xids", nmembers);
962 
963  /* safety check, we should never get this far in a HS standby */
964  if (RecoveryInProgress())
965  elog(ERROR, "cannot assign MultiXactIds during recovery");
966 
967  LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
968 
969  /* Handle wraparound of the nextMXact counter */
970  if (MultiXactState->nextMXact < FirstMultiXactId)
971  MultiXactState->nextMXact = FirstMultiXactId;
972 
973  /* Assign the MXID */
974  result = MultiXactState->nextMXact;
975 
976  /*----------
977  * Check to see if it's safe to assign another MultiXactId. This protects
978  * against catastrophic data loss due to multixact wraparound. The basic
979  * rules are:
980  *
981  * If we're past multiVacLimit or the safe threshold for member storage
982  * space, or we don't know what the safe threshold for member storage is,
983  * start trying to force autovacuum cycles.
984  * If we're past multiWarnLimit, start issuing warnings.
985  * If we're past multiStopLimit, refuse to create new MultiXactIds.
986  *
987  * Note these are pretty much the same protections in GetNewTransactionId.
988  *----------
989  */
990  if (!MultiXactIdPrecedes(result, MultiXactState->multiVacLimit))
991  {
992  /*
993  * For safety's sake, we release MultiXactGenLock while sending
994  * signals, warnings, etc. This is not so much because we care about
995  * preserving concurrency in this situation, as to avoid any
996  * possibility of deadlock while doing get_database_name(). First,
997  * copy all the shared values we'll need in this path.
998  */
999  MultiXactId multiWarnLimit = MultiXactState->multiWarnLimit;
1000  MultiXactId multiStopLimit = MultiXactState->multiStopLimit;
1001  MultiXactId multiWrapLimit = MultiXactState->multiWrapLimit;
1002  Oid oldest_datoid = MultiXactState->oldestMultiXactDB;
1003 
1004  LWLockRelease(MultiXactGenLock);
1005 
1006  if (IsUnderPostmaster &&
1007  !MultiXactIdPrecedes(result, multiStopLimit))
1008  {
1009  char *oldest_datname = get_database_name(oldest_datoid);
1010 
1011  /*
1012  * Immediately kick autovacuum into action as we're already in
1013  * ERROR territory.
1014  */
1016 
1017  /* complain even if that DB has disappeared */
1018  if (oldest_datname)
1019  ereport(ERROR,
1020  (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
1021  errmsg("database is not accepting commands that generate new MultiXactIds to avoid wraparound data loss in database \"%s\"",
1022  oldest_datname),
1023  errhint("Execute a database-wide VACUUM in that database.\n"
1024  "You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
1025  else
1026  ereport(ERROR,
1027  (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
1028  errmsg("database is not accepting commands that generate new MultiXactIds to avoid wraparound data loss in database with OID %u",
1029  oldest_datoid),
1030  errhint("Execute a database-wide VACUUM in that database.\n"
1031  "You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
1032  }
1033 
1034  /*
1035  * To avoid swamping the postmaster with signals, we issue the autovac
1036  * request only once per 64K multis generated. This still gives
1037  * plenty of chances before we get into real trouble.
1038  */
1039  if (IsUnderPostmaster && (result % 65536) == 0)
1041 
1042  if (!MultiXactIdPrecedes(result, multiWarnLimit))
1043  {
1044  char *oldest_datname = get_database_name(oldest_datoid);
1045 
1046  /* complain even if that DB has disappeared */
1047  if (oldest_datname)
1048  ereport(WARNING,
1049  (errmsg_plural("database \"%s\" must be vacuumed before %u more MultiXactId is used",
1050  "database \"%s\" must be vacuumed before %u more MultiXactIds are used",
1051  multiWrapLimit - result,
1052  oldest_datname,
1053  multiWrapLimit - result),
1054  errhint("Execute a database-wide VACUUM in that database.\n"
1055  "You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
1056  else
1057  ereport(WARNING,
1058  (errmsg_plural("database with OID %u must be vacuumed before %u more MultiXactId is used",
1059  "database with OID %u must be vacuumed before %u more MultiXactIds are used",
1060  multiWrapLimit - result,
1061  oldest_datoid,
1062  multiWrapLimit - result),
1063  errhint("Execute a database-wide VACUUM in that database.\n"
1064  "You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
1065  }
1066 
1067  /* Re-acquire lock and start over */
1068  LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
1069  result = MultiXactState->nextMXact;
1070  if (result < FirstMultiXactId)
1071  result = FirstMultiXactId;
1072  }
1073 
1074  /* Make sure there is room for the MXID in the file. */
1075  ExtendMultiXactOffset(result);
1076 
1077  /*
1078  * Reserve the members space, similarly to above. Also, be careful not to
1079  * return zero as the starting offset for any multixact. See
1080  * GetMultiXactIdMembers() for motivation.
1081  */
1082  nextOffset = MultiXactState->nextOffset;
1083  if (nextOffset == 0)
1084  {
1085  *offset = 1;
1086  nmembers++; /* allocate member slot 0 too */
1087  }
1088  else
1089  *offset = nextOffset;
1090 
1091  /*----------
1092  * Protect against overrun of the members space as well, with the
1093  * following rules:
1094  *
1095  * If we're past offsetStopLimit, refuse to generate more multis.
1096  * If we're close to offsetStopLimit, emit a warning.
1097  *
1098  * Arbitrarily, we start emitting warnings when we're 20 segments or less
1099  * from offsetStopLimit.
1100  *
1101  * Note we haven't updated the shared state yet, so if we fail at this
1102  * point, the multixact ID we grabbed can still be used by the next guy.
1103  *
1104  * Note that there is no point in forcing autovacuum runs here: the
1105  * multixact freeze settings would have to be reduced for that to have any
1106  * effect.
1107  *----------
1108  */
1109 #define OFFSET_WARN_SEGMENTS 20
1110  if (MultiXactState->oldestOffsetKnown &&
1111  MultiXactOffsetWouldWrap(MultiXactState->offsetStopLimit, nextOffset,
1112  nmembers))
1113  {
1114  /* see comment in the corresponding offsets wraparound case */
1116 
1117  ereport(ERROR,
1118  (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
1119  errmsg("multixact \"members\" limit exceeded"),
1120  errdetail_plural("This command would create a multixact with %u members, but the remaining space is only enough for %u member.",
1121  "This command would create a multixact with %u members, but the remaining space is only enough for %u members.",
1122  MultiXactState->offsetStopLimit - nextOffset - 1,
1123  nmembers,
1124  MultiXactState->offsetStopLimit - nextOffset - 1),
1125  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.",
1126  MultiXactState->oldestMultiXactDB)));
1127  }
1128 
1129  /*
1130  * Check whether we should kick autovacuum into action, to prevent members
1131  * wraparound. NB we use a much larger window to trigger autovacuum than
1132  * just the warning limit. The warning is just a measure of last resort -
1133  * this is in line with GetNewTransactionId's behaviour.
1134  */
1135  if (!MultiXactState->oldestOffsetKnown ||
1136  (MultiXactState->nextOffset - MultiXactState->oldestOffset
1138  {
1139  /*
1140  * To avoid swamping the postmaster with signals, we issue the autovac
1141  * request only when crossing a segment boundary. With default
1142  * compilation settings that's roughly after 50k members. This still
1143  * gives plenty of chances before we get into real trouble.
1144  */
1145  if ((MXOffsetToMemberPage(nextOffset) / SLRU_PAGES_PER_SEGMENT) !=
1146  (MXOffsetToMemberPage(nextOffset + nmembers) / SLRU_PAGES_PER_SEGMENT))
1148  }
1149 
1150  if (MultiXactState->oldestOffsetKnown &&
1151  MultiXactOffsetWouldWrap(MultiXactState->offsetStopLimit,
1152  nextOffset,
1154  ereport(WARNING,
1155  (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
1156  errmsg_plural("database with OID %u must be vacuumed before %d more multixact member is used",
1157  "database with OID %u must be vacuumed before %d more multixact members are used",
1158  MultiXactState->offsetStopLimit - nextOffset + nmembers,
1159  MultiXactState->oldestMultiXactDB,
1160  MultiXactState->offsetStopLimit - nextOffset + nmembers),
1161  errhint("Execute a database-wide VACUUM in that database with reduced vacuum_multixact_freeze_min_age and vacuum_multixact_freeze_table_age settings.")));
1162 
1163  ExtendMultiXactMember(nextOffset, nmembers);
1164 
1165  /*
1166  * Critical section from here until caller has written the data into the
1167  * just-reserved SLRU space; we don't want to error out with a partly
1168  * written MultiXact structure. (In particular, failing to write our
1169  * start offset after advancing nextMXact would effectively corrupt the
1170  * previous MultiXact.)
1171  */
1173 
1174  /*
1175  * Advance counters. As in GetNewTransactionId(), this must not happen
1176  * until after file extension has succeeded!
1177  *
1178  * We don't care about MultiXactId wraparound here; it will be handled by
1179  * the next iteration. But note that nextMXact may be InvalidMultiXactId
1180  * or the first value on a segment-beginning page after this routine
1181  * exits, so anyone else looking at the variable must be prepared to deal
1182  * with either case. Similarly, nextOffset may be zero, but we won't use
1183  * that as the actual start offset of the next multixact.
1184  */
1185  (MultiXactState->nextMXact)++;
1186 
1187  MultiXactState->nextOffset += nmembers;
1188 
1189  LWLockRelease(MultiXactGenLock);
1190 
1191  debug_elog4(DEBUG2, "GetNew: returning %u offset %u", result, *offset);
1192  return result;
1193 }
1194 
1195 /*
1196  * GetMultiXactIdMembers
1197  * Return the set of MultiXactMembers that make up a MultiXactId
1198  *
1199  * Return value is the number of members found, or -1 if there are none,
1200  * and *members is set to a newly palloc'ed array of members. It's the
1201  * caller's responsibility to free it when done with it.
1202  *
1203  * from_pgupgrade must be passed as true if and only if only the multixact
1204  * corresponds to a value from a tuple that was locked in a 9.2-or-older
1205  * installation and later pg_upgrade'd (that is, the infomask is
1206  * HEAP_LOCKED_UPGRADED). In this case, we know for certain that no members
1207  * can still be running, so we return -1 just like for an empty multixact
1208  * without any further checking. It would be wrong to try to resolve such a
1209  * multixact: either the multixact is within the current valid multixact
1210  * range, in which case the returned result would be bogus, or outside that
1211  * range, in which case an error would be raised.
1212  *
1213  * In all other cases, the passed multixact must be within the known valid
1214  * range, that is, greater to or equal than oldestMultiXactId, and less than
1215  * nextMXact. Otherwise, an error is raised.
1216  *
1217  * onlyLock must be set to true if caller is certain that the given multi
1218  * is used only to lock tuples; can be false without loss of correctness,
1219  * but passing a true means we can return quickly without checking for
1220  * old updates.
1221  */
1222 int
1224  bool from_pgupgrade, bool onlyLock)
1225 {
1226  int pageno;
1227  int prev_pageno;
1228  int entryno;
1229  int slotno;
1230  MultiXactOffset *offptr;
1231  MultiXactOffset offset;
1232  int length;
1233  int truelength;
1234  int i;
1235  MultiXactId oldestMXact;
1237  MultiXactId tmpMXact;
1239  MultiXactMember *ptr;
1240 
1241  debug_elog3(DEBUG2, "GetMembers: asked for %u", multi);
1242 
1243  if (!MultiXactIdIsValid(multi) || from_pgupgrade)
1244  {
1245  *members = NULL;
1246  return -1;
1247  }
1248 
1249  /* See if the MultiXactId is in the local cache */
1250  length = mXactCacheGetById(multi, members);
1251  if (length >= 0)
1252  {
1253  debug_elog3(DEBUG2, "GetMembers: found %s in the cache",
1254  mxid_to_string(multi, length, *members));
1255  return length;
1256  }
1257 
1258  /* Set our OldestVisibleMXactId[] entry if we didn't already */
1260 
1261  /*
1262  * If we know the multi is used only for locking and not for updates, then
1263  * we can skip checking if the value is older than our oldest visible
1264  * multi. It cannot possibly still be running.
1265  */
1266  if (onlyLock &&
1268  {
1269  debug_elog2(DEBUG2, "GetMembers: a locker-only multi is too old");
1270  *members = NULL;
1271  return -1;
1272  }
1273 
1274  /*
1275  * We check known limits on MultiXact before resorting to the SLRU area.
1276  *
1277  * An ID older than MultiXactState->oldestMultiXactId cannot possibly be
1278  * useful; it has already been removed, or will be removed shortly, by
1279  * truncation. If one is passed, an error is raised.
1280  *
1281  * Also, an ID >= nextMXact shouldn't ever be seen here; if it is seen, it
1282  * implies undetected ID wraparound has occurred. This raises a hard
1283  * error.
1284  *
1285  * Shared lock is enough here since we aren't modifying any global state.
1286  * Acquire it just long enough to grab the current counter values. We may
1287  * need both nextMXact and nextOffset; see below.
1288  */
1289  LWLockAcquire(MultiXactGenLock, LW_SHARED);
1290 
1291  oldestMXact = MultiXactState->oldestMultiXactId;
1292  nextMXact = MultiXactState->nextMXact;
1293  nextOffset = MultiXactState->nextOffset;
1294 
1295  LWLockRelease(MultiXactGenLock);
1296 
1297  if (MultiXactIdPrecedes(multi, oldestMXact))
1298  ereport(ERROR,
1299  (errcode(ERRCODE_INTERNAL_ERROR),
1300  errmsg("MultiXactId %u does no longer exist -- apparent wraparound",
1301  multi)));
1302 
1303  if (!MultiXactIdPrecedes(multi, nextMXact))
1304  ereport(ERROR,
1305  (errcode(ERRCODE_INTERNAL_ERROR),
1306  errmsg("MultiXactId %u has not been created yet -- apparent wraparound",
1307  multi)));
1308 
1309  /*
1310  * Find out the offset at which we need to start reading MultiXactMembers
1311  * and the number of members in the multixact. We determine the latter as
1312  * the difference between this multixact's starting offset and the next
1313  * one's. However, there are some corner cases to worry about:
1314  *
1315  * 1. This multixact may be the latest one created, in which case there is
1316  * no next one to look at. In this case the nextOffset value we just
1317  * saved is the correct endpoint.
1318  *
1319  * 2. The next multixact may still be in process of being filled in: that
1320  * is, another process may have done GetNewMultiXactId but not yet written
1321  * the offset entry for that ID. In that scenario, it is guaranteed that
1322  * the offset entry for that multixact exists (because GetNewMultiXactId
1323  * won't release MultiXactGenLock until it does) but contains zero
1324  * (because we are careful to pre-zero offset pages). Because
1325  * GetNewMultiXactId will never return zero as the starting offset for a
1326  * multixact, when we read zero as the next multixact's offset, we know we
1327  * have this case. We sleep for a bit and try again.
1328  *
1329  * 3. Because GetNewMultiXactId increments offset zero to offset one to
1330  * handle case #2, there is an ambiguity near the point of offset
1331  * wraparound. If we see next multixact's offset is one, is that our
1332  * multixact's actual endpoint, or did it end at zero with a subsequent
1333  * increment? We handle this using the knowledge that if the zero'th
1334  * member slot wasn't filled, it'll contain zero, and zero isn't a valid
1335  * transaction ID so it can't be a multixact member. Therefore, if we
1336  * read a zero from the members array, just ignore it.
1337  *
1338  * This is all pretty messy, but the mess occurs only in infrequent corner
1339  * cases, so it seems better than holding the MultiXactGenLock for a long
1340  * time on every multixact creation.
1341  */
1342 retry:
1343  LWLockAcquire(MultiXactOffsetSLRULock, LW_EXCLUSIVE);
1344 
1345  pageno = MultiXactIdToOffsetPage(multi);
1346  entryno = MultiXactIdToOffsetEntry(multi);
1347 
1348  slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, multi);
1349  offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
1350  offptr += entryno;
1351  offset = *offptr;
1352 
1353  Assert(offset != 0);
1354 
1355  /*
1356  * Use the same increment rule as GetNewMultiXactId(), that is, don't
1357  * handle wraparound explicitly until needed.
1358  */
1359  tmpMXact = multi + 1;
1360 
1361  if (nextMXact == tmpMXact)
1362  {
1363  /* Corner case 1: there is no next multixact */
1364  length = nextOffset - offset;
1365  }
1366  else
1367  {
1368  MultiXactOffset nextMXOffset;
1369 
1370  /* handle wraparound if needed */
1371  if (tmpMXact < FirstMultiXactId)
1372  tmpMXact = FirstMultiXactId;
1373 
1374  prev_pageno = pageno;
1375 
1376  pageno = MultiXactIdToOffsetPage(tmpMXact);
1377  entryno = MultiXactIdToOffsetEntry(tmpMXact);
1378 
1379  if (pageno != prev_pageno)
1380  slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, tmpMXact);
1381 
1382  offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
1383  offptr += entryno;
1384  nextMXOffset = *offptr;
1385 
1386  if (nextMXOffset == 0)
1387  {
1388  /* Corner case 2: next multixact is still being filled in */
1389  LWLockRelease(MultiXactOffsetSLRULock);
1391  pg_usleep(1000L);
1392  goto retry;
1393  }
1394 
1395  length = nextMXOffset - offset;
1396  }
1397 
1398  LWLockRelease(MultiXactOffsetSLRULock);
1399 
1400  ptr = (MultiXactMember *) palloc(length * sizeof(MultiXactMember));
1401 
1402  /* Now get the members themselves. */
1403  LWLockAcquire(MultiXactMemberSLRULock, LW_EXCLUSIVE);
1404 
1405  truelength = 0;
1406  prev_pageno = -1;
1407  for (i = 0; i < length; i++, offset++)
1408  {
1409  TransactionId *xactptr;
1410  uint32 *flagsptr;
1411  int flagsoff;
1412  int bshift;
1413  int memberoff;
1414 
1415  pageno = MXOffsetToMemberPage(offset);
1416  memberoff = MXOffsetToMemberOffset(offset);
1417 
1418  if (pageno != prev_pageno)
1419  {
1420  slotno = SimpleLruReadPage(MultiXactMemberCtl, pageno, true, multi);
1421  prev_pageno = pageno;
1422  }
1423 
1424  xactptr = (TransactionId *)
1425  (MultiXactMemberCtl->shared->page_buffer[slotno] + memberoff);
1426 
1427  if (!TransactionIdIsValid(*xactptr))
1428  {
1429  /* Corner case 3: we must be looking at unused slot zero */
1430  Assert(offset == 0);
1431  continue;
1432  }
1433 
1434  flagsoff = MXOffsetToFlagsOffset(offset);
1435  bshift = MXOffsetToFlagsBitShift(offset);
1436  flagsptr = (uint32 *) (MultiXactMemberCtl->shared->page_buffer[slotno] + flagsoff);
1437 
1438  ptr[truelength].xid = *xactptr;
1439  ptr[truelength].status = (*flagsptr >> bshift) & MXACT_MEMBER_XACT_BITMASK;
1440  truelength++;
1441  }
1442 
1443  LWLockRelease(MultiXactMemberSLRULock);
1444 
1445  /* A multixid with zero members should not happen */
1446  Assert(truelength > 0);
1447 
1448  /*
1449  * Copy the result into the local cache.
1450  */
1451  mXactCachePut(multi, truelength, ptr);
1452 
1453  debug_elog3(DEBUG2, "GetMembers: no cache for %s",
1454  mxid_to_string(multi, truelength, ptr));
1455  *members = ptr;
1456  return truelength;
1457 }
1458 
1459 /*
1460  * mxactMemberComparator
1461  * qsort comparison function for MultiXactMember
1462  *
1463  * We can't use wraparound comparison for XIDs because that does not respect
1464  * the triangle inequality! Any old sort order will do.
1465  */
1466 static int
1467 mxactMemberComparator(const void *arg1, const void *arg2)
1468 {
1469  MultiXactMember member1 = *(const MultiXactMember *) arg1;
1470  MultiXactMember member2 = *(const MultiXactMember *) arg2;
1471 
1472  if (member1.xid > member2.xid)
1473  return 1;
1474  if (member1.xid < member2.xid)
1475  return -1;
1476  if (member1.status > member2.status)
1477  return 1;
1478  if (member1.status < member2.status)
1479  return -1;
1480  return 0;
1481 }
1482 
1483 /*
1484  * mXactCacheGetBySet
1485  * returns a MultiXactId from the cache based on the set of
1486  * TransactionIds that compose it, or InvalidMultiXactId if
1487  * none matches.
1488  *
1489  * This is helpful, for example, if two transactions want to lock a huge
1490  * table. By using the cache, the second will use the same MultiXactId
1491  * for the majority of tuples, thus keeping MultiXactId usage low (saving
1492  * both I/O and wraparound issues).
1493  *
1494  * NB: the passed members array will be sorted in-place.
1495  */
1496 static MultiXactId
1497 mXactCacheGetBySet(int nmembers, MultiXactMember *members)
1498 {
1499  dlist_iter iter;
1500 
1501  debug_elog3(DEBUG2, "CacheGet: looking for %s",
1502  mxid_to_string(InvalidMultiXactId, nmembers, members));
1503 
1504  /* sort the array so comparison is easy */
1505  qsort(members, nmembers, sizeof(MultiXactMember), mxactMemberComparator);
1506 
1507  dlist_foreach(iter, &MXactCache)
1508  {
1509  mXactCacheEnt *entry = dlist_container(mXactCacheEnt, node, iter.cur);
1510 
1511  if (entry->nmembers != nmembers)
1512  continue;
1513 
1514  /*
1515  * We assume the cache entries are sorted, and that the unused bits in
1516  * "status" are zeroed.
1517  */
1518  if (memcmp(members, entry->members, nmembers * sizeof(MultiXactMember)) == 0)
1519  {
1520  debug_elog3(DEBUG2, "CacheGet: found %u", entry->multi);
1521  dlist_move_head(&MXactCache, iter.cur);
1522  return entry->multi;
1523  }
1524  }
1525 
1526  debug_elog2(DEBUG2, "CacheGet: not found :-(");
1527  return InvalidMultiXactId;
1528 }
1529 
1530 /*
1531  * mXactCacheGetById
1532  * returns the composing MultiXactMember set from the cache for a
1533  * given MultiXactId, if present.
1534  *
1535  * If successful, *xids is set to the address of a palloc'd copy of the
1536  * MultiXactMember set. Return value is number of members, or -1 on failure.
1537  */
1538 static int
1540 {
1541  dlist_iter iter;
1542 
1543  debug_elog3(DEBUG2, "CacheGet: looking for %u", multi);
1544 
1545  dlist_foreach(iter, &MXactCache)
1546  {
1547  mXactCacheEnt *entry = dlist_container(mXactCacheEnt, node, iter.cur);
1548 
1549  if (entry->multi == multi)
1550  {
1551  MultiXactMember *ptr;
1552  Size size;
1553 
1554  size = sizeof(MultiXactMember) * entry->nmembers;
1555  ptr = (MultiXactMember *) palloc(size);
1556 
1557  memcpy(ptr, entry->members, size);
1558 
1559  debug_elog3(DEBUG2, "CacheGet: found %s",
1560  mxid_to_string(multi,
1561  entry->nmembers,
1562  entry->members));
1563 
1564  /*
1565  * Note we modify the list while not using a modifiable iterator.
1566  * This is acceptable only because we exit the iteration
1567  * immediately afterwards.
1568  */
1569  dlist_move_head(&MXactCache, iter.cur);
1570 
1571  *members = ptr;
1572  return entry->nmembers;
1573  }
1574  }
1575 
1576  debug_elog2(DEBUG2, "CacheGet: not found");
1577  return -1;
1578 }
1579 
1580 /*
1581  * mXactCachePut
1582  * Add a new MultiXactId and its composing set into the local cache.
1583  */
1584 static void
1585 mXactCachePut(MultiXactId multi, int nmembers, MultiXactMember *members)
1586 {
1587  mXactCacheEnt *entry;
1588 
1589  debug_elog3(DEBUG2, "CachePut: storing %s",
1590  mxid_to_string(multi, nmembers, members));
1591 
1592  if (MXactContext == NULL)
1593  {
1594  /* The cache only lives as long as the current transaction */
1595  debug_elog2(DEBUG2, "CachePut: initializing memory context");
1597  "MultiXact cache context",
1599  }
1600 
1601  entry = (mXactCacheEnt *)
1602  MemoryContextAlloc(MXactContext,
1603  offsetof(mXactCacheEnt, members) +
1604  nmembers * sizeof(MultiXactMember));
1605 
1606  entry->multi = multi;
1607  entry->nmembers = nmembers;
1608  memcpy(entry->members, members, nmembers * sizeof(MultiXactMember));
1609 
1610  /* mXactCacheGetBySet assumes the entries are sorted, so sort them */
1611  qsort(entry->members, nmembers, sizeof(MultiXactMember), mxactMemberComparator);
1612 
1613  dlist_push_head(&MXactCache, &entry->node);
1615  {
1616  dlist_node *node;
1617  mXactCacheEnt *entry;
1618 
1619  node = dlist_tail_node(&MXactCache);
1620  dlist_delete(node);
1622 
1623  entry = dlist_container(mXactCacheEnt, node, node);
1624  debug_elog3(DEBUG2, "CachePut: pruning cached multi %u",
1625  entry->multi);
1626 
1627  pfree(entry);
1628  }
1629 }
1630 
1631 static char *
1633 {
1634  switch (status)
1635  {
1637  return "keysh";
1639  return "sh";
1641  return "fornokeyupd";
1643  return "forupd";
1645  return "nokeyupd";
1646  case MultiXactStatusUpdate:
1647  return "upd";
1648  default:
1649  elog(ERROR, "unrecognized multixact status %d", status);
1650  return "";
1651  }
1652 }
1653 
1654 char *
1655 mxid_to_string(MultiXactId multi, int nmembers, MultiXactMember *members)
1656 {
1657  static char *str = NULL;
1659  int i;
1660 
1661  if (str != NULL)
1662  pfree(str);
1663 
1664  initStringInfo(&buf);
1665 
1666  appendStringInfo(&buf, "%u %d[%u (%s)", multi, nmembers, members[0].xid,
1667  mxstatus_to_string(members[0].status));
1668 
1669  for (i = 1; i < nmembers; i++)
1670  appendStringInfo(&buf, ", %u (%s)", members[i].xid,
1671  mxstatus_to_string(members[i].status));
1672 
1673  appendStringInfoChar(&buf, ']');
1675  pfree(buf.data);
1676  return str;
1677 }
1678 
1679 /*
1680  * AtEOXact_MultiXact
1681  * Handle transaction end for MultiXact
1682  *
1683  * This is called at top transaction commit or abort (we don't care which).
1684  */
1685 void
1687 {
1688  /*
1689  * Reset our OldestMemberMXactId and OldestVisibleMXactId values, both of
1690  * which should only be valid while within a transaction.
1691  *
1692  * We assume that storing a MultiXactId is atomic and so we need not take
1693  * MultiXactGenLock to do this.
1694  */
1697 
1698  /*
1699  * Discard the local MultiXactId cache. Since MXactContext was created as
1700  * a child of TopTransactionContext, we needn't delete it explicitly.
1701  */
1702  MXactContext = NULL;
1703  dlist_init(&MXactCache);
1704  MXactCacheMembers = 0;
1705 }
1706 
1707 /*
1708  * AtPrepare_MultiXact
1709  * Save multixact state at 2PC transaction prepare
1710  *
1711  * In this phase, we only store our OldestMemberMXactId value in the two-phase
1712  * state file.
1713  */
1714 void
1716 {
1717  MultiXactId myOldestMember = OldestMemberMXactId[MyBackendId];
1718 
1719  if (MultiXactIdIsValid(myOldestMember))
1721  &myOldestMember, sizeof(MultiXactId));
1722 }
1723 
1724 /*
1725  * PostPrepare_MultiXact
1726  * Clean up after successful PREPARE TRANSACTION
1727  */
1728 void
1730 {
1731  MultiXactId myOldestMember;
1732 
1733  /*
1734  * Transfer our OldestMemberMXactId value to the slot reserved for the
1735  * prepared transaction.
1736  */
1737  myOldestMember = OldestMemberMXactId[MyBackendId];
1738  if (MultiXactIdIsValid(myOldestMember))
1739  {
1740  BackendId dummyBackendId = TwoPhaseGetDummyBackendId(xid, false);
1741 
1742  /*
1743  * Even though storing MultiXactId is atomic, acquire lock to make
1744  * sure others see both changes, not just the reset of the slot of the
1745  * current backend. Using a volatile pointer might suffice, but this
1746  * isn't a hot spot.
1747  */
1748  LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
1749 
1750  OldestMemberMXactId[dummyBackendId] = myOldestMember;
1752 
1753  LWLockRelease(MultiXactGenLock);
1754  }
1755 
1756  /*
1757  * We don't need to transfer OldestVisibleMXactId value, because the
1758  * transaction is not going to be looking at any more multixacts once it's
1759  * prepared.
1760  *
1761  * We assume that storing a MultiXactId is atomic and so we need not take
1762  * MultiXactGenLock to do this.
1763  */
1765 
1766  /*
1767  * Discard the local MultiXactId cache like in AtEOXact_MultiXact.
1768  */
1769  MXactContext = NULL;
1770  dlist_init(&MXactCache);
1771  MXactCacheMembers = 0;
1772 }
1773 
1774 /*
1775  * multixact_twophase_recover
1776  * Recover the state of a prepared transaction at startup
1777  */
1778 void
1780  void *recdata, uint32 len)
1781 {
1782  BackendId dummyBackendId = TwoPhaseGetDummyBackendId(xid, false);
1783  MultiXactId oldestMember;
1784 
1785  /*
1786  * Get the oldest member XID from the state file record, and set it in the
1787  * OldestMemberMXactId slot reserved for this prepared transaction.
1788  */
1789  Assert(len == sizeof(MultiXactId));
1790  oldestMember = *((MultiXactId *) recdata);
1791 
1792  OldestMemberMXactId[dummyBackendId] = oldestMember;
1793 }
1794 
1795 /*
1796  * multixact_twophase_postcommit
1797  * Similar to AtEOXact_MultiXact but for COMMIT PREPARED
1798  */
1799 void
1801  void *recdata, uint32 len)
1802 {
1803  BackendId dummyBackendId = TwoPhaseGetDummyBackendId(xid, true);
1804 
1805  Assert(len == sizeof(MultiXactId));
1806 
1807  OldestMemberMXactId[dummyBackendId] = InvalidMultiXactId;
1808 }
1809 
1810 /*
1811  * multixact_twophase_postabort
1812  * This is actually just the same as the COMMIT case.
1813  */
1814 void
1816  void *recdata, uint32 len)
1817 {
1818  multixact_twophase_postcommit(xid, info, recdata, len);
1819 }
1820 
1821 /*
1822  * Initialization of shared memory for MultiXact. We use two SLRU areas,
1823  * thus double memory. Also, reserve space for the shared MultiXactState
1824  * struct and the per-backend MultiXactId arrays (two of those, too).
1825  */
1826 Size
1828 {
1829  Size size;
1830 
1831  /* We need 2*MaxOldestSlot + 1 perBackendXactIds[] entries */
1832 #define SHARED_MULTIXACT_STATE_SIZE \
1833  add_size(offsetof(MultiXactStateData, perBackendXactIds) + sizeof(MultiXactId), \
1834  mul_size(sizeof(MultiXactId) * 2, MaxOldestSlot))
1835 
1839 
1840  return size;
1841 }
1842 
1843 void
1845 {
1846  bool found;
1847 
1848  debug_elog2(DEBUG2, "Shared Memory Init for MultiXact");
1849 
1852 
1854  "MultiXactOffset", NUM_MULTIXACTOFFSET_BUFFERS, 0,
1855  MultiXactOffsetSLRULock, "pg_multixact/offsets",
1860  "MultiXactMember", NUM_MULTIXACTMEMBER_BUFFERS, 0,
1861  MultiXactMemberSLRULock, "pg_multixact/members",
1864  /* doesn't call SimpleLruTruncate() or meet criteria for unit tests */
1865 
1866  /* Initialize our shared state struct */
1867  MultiXactState = ShmemInitStruct("Shared MultiXact State",
1869  &found);
1870  if (!IsUnderPostmaster)
1871  {
1872  Assert(!found);
1873 
1874  /* Make sure we zero out the per-backend state */
1875  MemSet(MultiXactState, 0, SHARED_MULTIXACT_STATE_SIZE);
1876  }
1877  else
1878  Assert(found);
1879 
1880  /*
1881  * Set up array pointers. Note that perBackendXactIds[0] is wasted space
1882  * since we only use indexes 1..MaxOldestSlot in each array.
1883  */
1884  OldestMemberMXactId = MultiXactState->perBackendXactIds;
1886 }
1887 
1888 /*
1889  * This func must be called ONCE on system install. It creates the initial
1890  * MultiXact segments. (The MultiXacts directories are assumed to have been
1891  * created by initdb, and MultiXactShmemInit must have been called already.)
1892  */
1893 void
1895 {
1896  int slotno;
1897 
1898  LWLockAcquire(MultiXactOffsetSLRULock, LW_EXCLUSIVE);
1899 
1900  /* Create and zero the first page of the offsets log */
1901  slotno = ZeroMultiXactOffsetPage(0, false);
1902 
1903  /* Make sure it's written out */
1905  Assert(!MultiXactOffsetCtl->shared->page_dirty[slotno]);
1906 
1907  LWLockRelease(MultiXactOffsetSLRULock);
1908 
1909  LWLockAcquire(MultiXactMemberSLRULock, LW_EXCLUSIVE);
1910 
1911  /* Create and zero the first page of the members log */
1912  slotno = ZeroMultiXactMemberPage(0, false);
1913 
1914  /* Make sure it's written out */
1916  Assert(!MultiXactMemberCtl->shared->page_dirty[slotno]);
1917 
1918  LWLockRelease(MultiXactMemberSLRULock);
1919 }
1920 
1921 /*
1922  * Initialize (or reinitialize) a page of MultiXactOffset to zeroes.
1923  * If writeXlog is true, also emit an XLOG record saying we did this.
1924  *
1925  * The page is not actually written, just set up in shared memory.
1926  * The slot number of the new page is returned.
1927  *
1928  * Control lock must be held at entry, and will be held at exit.
1929  */
1930 static int
1931 ZeroMultiXactOffsetPage(int pageno, bool writeXlog)
1932 {
1933  int slotno;
1934 
1935  slotno = SimpleLruZeroPage(MultiXactOffsetCtl, pageno);
1936 
1937  if (writeXlog)
1939 
1940  return slotno;
1941 }
1942 
1943 /*
1944  * Ditto, for MultiXactMember
1945  */
1946 static int
1947 ZeroMultiXactMemberPage(int pageno, bool writeXlog)
1948 {
1949  int slotno;
1950 
1951  slotno = SimpleLruZeroPage(MultiXactMemberCtl, pageno);
1952 
1953  if (writeXlog)
1955 
1956  return slotno;
1957 }
1958 
1959 /*
1960  * MaybeExtendOffsetSlru
1961  * Extend the offsets SLRU area, if necessary
1962  *
1963  * After a binary upgrade from <= 9.2, the pg_multixact/offsets SLRU area might
1964  * contain files that are shorter than necessary; this would occur if the old
1965  * installation had used multixacts beyond the first page (files cannot be
1966  * copied, because the on-disk representation is different). pg_upgrade would
1967  * update pg_control to set the next offset value to be at that position, so
1968  * that tuples marked as locked by such MultiXacts would be seen as visible
1969  * without having to consult multixact. However, trying to create and use a
1970  * new MultiXactId would result in an error because the page on which the new
1971  * value would reside does not exist. This routine is in charge of creating
1972  * such pages.
1973  */
1974 static void
1976 {
1977  int pageno;
1978 
1979  pageno = MultiXactIdToOffsetPage(MultiXactState->nextMXact);
1980 
1981  LWLockAcquire(MultiXactOffsetSLRULock, LW_EXCLUSIVE);
1982 
1984  {
1985  int slotno;
1986 
1987  /*
1988  * Fortunately for us, SimpleLruWritePage is already prepared to deal
1989  * with creating a new segment file even if the page we're writing is
1990  * not the first in it, so this is enough.
1991  */
1992  slotno = ZeroMultiXactOffsetPage(pageno, false);
1994  }
1995 
1996  LWLockRelease(MultiXactOffsetSLRULock);
1997 }
1998 
1999 /*
2000  * This must be called ONCE during postmaster or standalone-backend startup.
2001  *
2002  * StartupXLOG has already established nextMXact/nextOffset by calling
2003  * MultiXactSetNextMXact and/or MultiXactAdvanceNextMXact, and the oldestMulti
2004  * info from pg_control and/or MultiXactAdvanceOldest, but we haven't yet
2005  * replayed WAL.
2006  */
2007 void
2009 {
2010  MultiXactId multi = MultiXactState->nextMXact;
2011  MultiXactOffset offset = MultiXactState->nextOffset;
2012  int pageno;
2013 
2014  /*
2015  * Initialize offset's idea of the latest page number.
2016  */
2017  pageno = MultiXactIdToOffsetPage(multi);
2018  MultiXactOffsetCtl->shared->latest_page_number = pageno;
2019 
2020  /*
2021  * Initialize member's idea of the latest page number.
2022  */
2023  pageno = MXOffsetToMemberPage(offset);
2024  MultiXactMemberCtl->shared->latest_page_number = pageno;
2025 }
2026 
2027 /*
2028  * This must be called ONCE at the end of startup/recovery.
2029  */
2030 void
2032 {
2034  MultiXactOffset offset;
2035  MultiXactId oldestMXact;
2036  Oid oldestMXactDB;
2037  int pageno;
2038  int entryno;
2039  int flagsoff;
2040 
2041  LWLockAcquire(MultiXactGenLock, LW_SHARED);
2042  nextMXact = MultiXactState->nextMXact;
2043  offset = MultiXactState->nextOffset;
2044  oldestMXact = MultiXactState->oldestMultiXactId;
2045  oldestMXactDB = MultiXactState->oldestMultiXactDB;
2046  LWLockRelease(MultiXactGenLock);
2047 
2048  /* Clean up offsets state */
2049  LWLockAcquire(MultiXactOffsetSLRULock, LW_EXCLUSIVE);
2050 
2051  /*
2052  * (Re-)Initialize our idea of the latest page number for offsets.
2053  */
2054  pageno = MultiXactIdToOffsetPage(nextMXact);
2055  MultiXactOffsetCtl->shared->latest_page_number = pageno;
2056 
2057  /*
2058  * Zero out the remainder of the current offsets page. See notes in
2059  * TrimCLOG() for background. Unlike CLOG, some WAL record covers every
2060  * pg_multixact SLRU mutation. Since, also unlike CLOG, we ignore the WAL
2061  * rule "write xlog before data," nextMXact successors may carry obsolete,
2062  * nonzero offset values. Zero those so case 2 of GetMultiXactIdMembers()
2063  * operates normally.
2064  */
2065  entryno = MultiXactIdToOffsetEntry(nextMXact);
2066  if (entryno != 0)
2067  {
2068  int slotno;
2069  MultiXactOffset *offptr;
2070 
2071  slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, nextMXact);
2072  offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
2073  offptr += entryno;
2074 
2075  MemSet(offptr, 0, BLCKSZ - (entryno * sizeof(MultiXactOffset)));
2076 
2077  MultiXactOffsetCtl->shared->page_dirty[slotno] = true;
2078  }
2079 
2080  LWLockRelease(MultiXactOffsetSLRULock);
2081 
2082  /* And the same for members */
2083  LWLockAcquire(MultiXactMemberSLRULock, LW_EXCLUSIVE);
2084 
2085  /*
2086  * (Re-)Initialize our idea of the latest page number for members.
2087  */
2088  pageno = MXOffsetToMemberPage(offset);
2089  MultiXactMemberCtl->shared->latest_page_number = pageno;
2090 
2091  /*
2092  * Zero out the remainder of the current members page. See notes in
2093  * TrimCLOG() for motivation.
2094  */
2095  flagsoff = MXOffsetToFlagsOffset(offset);
2096  if (flagsoff != 0)
2097  {
2098  int slotno;
2099  TransactionId *xidptr;
2100  int memberoff;
2101 
2102  memberoff = MXOffsetToMemberOffset(offset);
2103  slotno = SimpleLruReadPage(MultiXactMemberCtl, pageno, true, offset);
2104  xidptr = (TransactionId *)
2105  (MultiXactMemberCtl->shared->page_buffer[slotno] + memberoff);
2106 
2107  MemSet(xidptr, 0, BLCKSZ - memberoff);
2108 
2109  /*
2110  * Note: we don't need to zero out the flag bits in the remaining
2111  * members of the current group, because they are always reset before
2112  * writing.
2113  */
2114 
2115  MultiXactMemberCtl->shared->page_dirty[slotno] = true;
2116  }
2117 
2118  LWLockRelease(MultiXactMemberSLRULock);
2119 
2120  /* signal that we're officially up */
2121  LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
2122  MultiXactState->finishedStartup = true;
2123  LWLockRelease(MultiXactGenLock);
2124 
2125  /* Now compute how far away the next members wraparound is. */
2126  SetMultiXactIdLimit(oldestMXact, oldestMXactDB, true);
2127 }
2128 
2129 /*
2130  * Get the MultiXact data to save in a checkpoint record
2131  */
2132 void
2133 MultiXactGetCheckptMulti(bool is_shutdown,
2134  MultiXactId *nextMulti,
2135  MultiXactOffset *nextMultiOffset,
2136  MultiXactId *oldestMulti,
2137  Oid *oldestMultiDB)
2138 {
2139  LWLockAcquire(MultiXactGenLock, LW_SHARED);
2140  *nextMulti = MultiXactState->nextMXact;
2141  *nextMultiOffset = MultiXactState->nextOffset;
2142  *oldestMulti = MultiXactState->oldestMultiXactId;
2143  *oldestMultiDB = MultiXactState->oldestMultiXactDB;
2144  LWLockRelease(MultiXactGenLock);
2145 
2147  "MultiXact: checkpoint is nextMulti %u, nextOffset %u, oldestMulti %u in DB %u",
2148  *nextMulti, *nextMultiOffset, *oldestMulti, *oldestMultiDB);
2149 }
2150 
2151 /*
2152  * Perform a checkpoint --- either during shutdown, or on-the-fly
2153  */
2154 void
2156 {
2157  TRACE_POSTGRESQL_MULTIXACT_CHECKPOINT_START(true);
2158 
2159  /*
2160  * Write dirty MultiXact pages to disk. This may result in sync requests
2161  * queued for later handling by ProcessSyncRequests(), as part of the
2162  * checkpoint.
2163  */
2166 
2167  TRACE_POSTGRESQL_MULTIXACT_CHECKPOINT_DONE(true);
2168 }
2169 
2170 /*
2171  * Set the next-to-be-assigned MultiXactId and offset
2172  *
2173  * This is used when we can determine the correct next ID/offset exactly
2174  * from a checkpoint record. Although this is only called during bootstrap
2175  * and XLog replay, we take the lock in case any hot-standby backends are
2176  * examining the values.
2177  */
2178 void
2180  MultiXactOffset nextMultiOffset)
2181 {
2182  debug_elog4(DEBUG2, "MultiXact: setting next multi to %u offset %u",
2183  nextMulti, nextMultiOffset);
2184  LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
2185  MultiXactState->nextMXact = nextMulti;
2186  MultiXactState->nextOffset = nextMultiOffset;
2187  LWLockRelease(MultiXactGenLock);
2188 
2189  /*
2190  * During a binary upgrade, make sure that the offsets SLRU is large
2191  * enough to contain the next value that would be created.
2192  *
2193  * We need to do this pretty early during the first startup in binary
2194  * upgrade mode: before StartupMultiXact() in fact, because this routine
2195  * is called even before that by StartupXLOG(). And we can't do it
2196  * earlier than at this point, because during that first call of this
2197  * routine we determine the MultiXactState->nextMXact value that
2198  * MaybeExtendOffsetSlru needs.
2199  */
2200  if (IsBinaryUpgrade)
2202 }
2203 
2204 /*
2205  * Determine the last safe MultiXactId to allocate given the currently oldest
2206  * datminmxid (ie, the oldest MultiXactId that might exist in any database
2207  * of our cluster), and the OID of the (or a) database with that value.
2208  *
2209  * is_startup is true when we are just starting the cluster, false when we
2210  * are updating state in a running cluster. This only affects log messages.
2211  */
2212 void
2213 SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid,
2214  bool is_startup)
2215 {
2220  MultiXactId curMulti;
2221  bool needs_offset_vacuum;
2222 
2223  Assert(MultiXactIdIsValid(oldest_datminmxid));
2224 
2225  /*
2226  * We pretend that a wrap will happen halfway through the multixact ID
2227  * space, but that's not really true, because multixacts wrap differently
2228  * from transaction IDs. Note that, separately from any concern about
2229  * multixact IDs wrapping, we must ensure that multixact members do not
2230  * wrap. Limits for that are set in SetOffsetVacuumLimit, not here.
2231  */
2232  multiWrapLimit = oldest_datminmxid + (MaxMultiXactId >> 1);
2233  if (multiWrapLimit < FirstMultiXactId)
2234  multiWrapLimit += FirstMultiXactId;
2235 
2236  /*
2237  * We'll refuse to continue assigning MultiXactIds once we get within 3M
2238  * multi of data loss. See SetTransactionIdLimit.
2239  */
2240  multiStopLimit = multiWrapLimit - 3000000;
2241  if (multiStopLimit < FirstMultiXactId)
2242  multiStopLimit -= FirstMultiXactId;
2243 
2244  /*
2245  * We'll start complaining loudly when we get within 40M multis of data
2246  * loss. This is kind of arbitrary, but if you let your gas gauge get
2247  * down to 2% of full, would you be looking for the next gas station? We
2248  * need to be fairly liberal about this number because there are lots of
2249  * scenarios where most transactions are done by automatic clients that
2250  * won't pay attention to warnings. (No, we're not gonna make this
2251  * configurable. If you know enough to configure it, you know enough to
2252  * not get in this kind of trouble in the first place.)
2253  */
2254  multiWarnLimit = multiWrapLimit - 40000000;
2255  if (multiWarnLimit < FirstMultiXactId)
2256  multiWarnLimit -= FirstMultiXactId;
2257 
2258  /*
2259  * We'll start trying to force autovacuums when oldest_datminmxid gets to
2260  * be more than autovacuum_multixact_freeze_max_age mxids old.
2261  *
2262  * Note: autovacuum_multixact_freeze_max_age is a PGC_POSTMASTER parameter
2263  * so that we don't have to worry about dealing with on-the-fly changes in
2264  * its value. See SetTransactionIdLimit.
2265  */
2266  multiVacLimit = oldest_datminmxid + autovacuum_multixact_freeze_max_age;
2267  if (multiVacLimit < FirstMultiXactId)
2268  multiVacLimit += FirstMultiXactId;
2269 
2270  /* Grab lock for just long enough to set the new limit values */
2271  LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
2272  MultiXactState->oldestMultiXactId = oldest_datminmxid;
2273  MultiXactState->oldestMultiXactDB = oldest_datoid;
2274  MultiXactState->multiVacLimit = multiVacLimit;
2275  MultiXactState->multiWarnLimit = multiWarnLimit;
2276  MultiXactState->multiStopLimit = multiStopLimit;
2277  MultiXactState->multiWrapLimit = multiWrapLimit;
2278  curMulti = MultiXactState->nextMXact;
2279  LWLockRelease(MultiXactGenLock);
2280 
2281  /* Log the info */
2282  ereport(DEBUG1,
2283  (errmsg_internal("MultiXactId wrap limit is %u, limited by database with OID %u",
2284  multiWrapLimit, oldest_datoid)));
2285 
2286  /*
2287  * Computing the actual limits is only possible once the data directory is
2288  * in a consistent state. There's no need to compute the limits while
2289  * still replaying WAL - no decisions about new multis are made even
2290  * though multixact creations might be replayed. So we'll only do further
2291  * checks after TrimMultiXact() has been called.
2292  */
2293  if (!MultiXactState->finishedStartup)
2294  return;
2295 
2296  Assert(!InRecovery);
2297 
2298  /* Set limits for offset vacuum. */
2299  needs_offset_vacuum = SetOffsetVacuumLimit(is_startup);
2300 
2301  /*
2302  * If past the autovacuum force point, immediately signal an autovac
2303  * request. The reason for this is that autovac only processes one
2304  * database per invocation. Once it's finished cleaning up the oldest
2305  * database, it'll call here, and we'll signal the postmaster to start
2306  * another iteration immediately if there are still any old databases.
2307  */
2308  if ((MultiXactIdPrecedes(multiVacLimit, curMulti) ||
2309  needs_offset_vacuum) && IsUnderPostmaster)
2311 
2312  /* Give an immediate warning if past the wrap warn point */
2313  if (MultiXactIdPrecedes(multiWarnLimit, curMulti))
2314  {
2315  char *oldest_datname;
2316 
2317  /*
2318  * We can be called when not inside a transaction, for example during
2319  * StartupXLOG(). In such a case we cannot do database access, so we
2320  * must just report the oldest DB's OID.
2321  *
2322  * Note: it's also possible that get_database_name fails and returns
2323  * NULL, for example because the database just got dropped. We'll
2324  * still warn, even though the warning might now be unnecessary.
2325  */
2326  if (IsTransactionState())
2327  oldest_datname = get_database_name(oldest_datoid);
2328  else
2329  oldest_datname = NULL;
2330 
2331  if (oldest_datname)
2332  ereport(WARNING,
2333  (errmsg_plural("database \"%s\" must be vacuumed before %u more MultiXactId is used",
2334  "database \"%s\" must be vacuumed before %u more MultiXactIds are used",
2335  multiWrapLimit - curMulti,
2336  oldest_datname,
2337  multiWrapLimit - curMulti),
2338  errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
2339  "You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
2340  else
2341  ereport(WARNING,
2342  (errmsg_plural("database with OID %u must be vacuumed before %u more MultiXactId is used",
2343  "database with OID %u must be vacuumed before %u more MultiXactIds are used",
2344  multiWrapLimit - curMulti,
2345  oldest_datoid,
2346  multiWrapLimit - curMulti),
2347  errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
2348  "You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
2349  }
2350 }
2351 
2352 /*
2353  * Ensure the next-to-be-assigned MultiXactId is at least minMulti,
2354  * and similarly nextOffset is at least minMultiOffset.
2355  *
2356  * This is used when we can determine minimum safe values from an XLog
2357  * record (either an on-line checkpoint or an mxact creation log entry).
2358  * Although this is only called during XLog replay, we take the lock in case
2359  * any hot-standby backends are examining the values.
2360  */
2361 void
2363  MultiXactOffset minMultiOffset)
2364 {
2365  LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
2366  if (MultiXactIdPrecedes(MultiXactState->nextMXact, minMulti))
2367  {
2368  debug_elog3(DEBUG2, "MultiXact: setting next multi to %u", minMulti);
2369  MultiXactState->nextMXact = minMulti;
2370  }
2371  if (MultiXactOffsetPrecedes(MultiXactState->nextOffset, minMultiOffset))
2372  {
2373  debug_elog3(DEBUG2, "MultiXact: setting next offset to %u",
2374  minMultiOffset);
2375  MultiXactState->nextOffset = minMultiOffset;
2376  }
2377  LWLockRelease(MultiXactGenLock);
2378 }
2379 
2380 /*
2381  * Update our oldestMultiXactId value, but only if it's more recent than what
2382  * we had.
2383  *
2384  * This may only be called during WAL replay.
2385  */
2386 void
2387 MultiXactAdvanceOldest(MultiXactId oldestMulti, Oid oldestMultiDB)
2388 {
2389  Assert(InRecovery);
2390 
2391  if (MultiXactIdPrecedes(MultiXactState->oldestMultiXactId, oldestMulti))
2392  SetMultiXactIdLimit(oldestMulti, oldestMultiDB, false);
2393 }
2394 
2395 /*
2396  * Make sure that MultiXactOffset has room for a newly-allocated MultiXactId.
2397  *
2398  * NB: this is called while holding MultiXactGenLock. We want it to be very
2399  * fast most of the time; even when it's not so fast, no actual I/O need
2400  * happen unless we're forced to write out a dirty log or xlog page to make
2401  * room in shared memory.
2402  */
2403 static void
2405 {
2406  int pageno;
2407 
2408  /*
2409  * No work except at first MultiXactId of a page. But beware: just after
2410  * wraparound, the first MultiXactId of page zero is FirstMultiXactId.
2411  */
2412  if (MultiXactIdToOffsetEntry(multi) != 0 &&
2413  multi != FirstMultiXactId)
2414  return;
2415 
2416  pageno = MultiXactIdToOffsetPage(multi);
2417 
2418  LWLockAcquire(MultiXactOffsetSLRULock, LW_EXCLUSIVE);
2419 
2420  /* Zero the page and make an XLOG entry about it */
2421  ZeroMultiXactOffsetPage(pageno, true);
2422 
2423  LWLockRelease(MultiXactOffsetSLRULock);
2424 }
2425 
2426 /*
2427  * Make sure that MultiXactMember has room for the members of a newly-
2428  * allocated MultiXactId.
2429  *
2430  * Like the above routine, this is called while holding MultiXactGenLock;
2431  * same comments apply.
2432  */
2433 static void
2435 {
2436  /*
2437  * It's possible that the members span more than one page of the members
2438  * file, so we loop to ensure we consider each page. The coding is not
2439  * optimal if the members span several pages, but that seems unusual
2440  * enough to not worry much about.
2441  */
2442  while (nmembers > 0)
2443  {
2444  int flagsoff;
2445  int flagsbit;
2447 
2448  /*
2449  * Only zero when at first entry of a page.
2450  */
2451  flagsoff = MXOffsetToFlagsOffset(offset);
2452  flagsbit = MXOffsetToFlagsBitShift(offset);
2453  if (flagsoff == 0 && flagsbit == 0)
2454  {
2455  int pageno;
2456 
2457  pageno = MXOffsetToMemberPage(offset);
2458 
2459  LWLockAcquire(MultiXactMemberSLRULock, LW_EXCLUSIVE);
2460 
2461  /* Zero the page and make an XLOG entry about it */
2462  ZeroMultiXactMemberPage(pageno, true);
2463 
2464  LWLockRelease(MultiXactMemberSLRULock);
2465  }
2466 
2467  /*
2468  * Compute the number of items till end of current page. Careful: if
2469  * addition of unsigned ints wraps around, we're at the last page of
2470  * the last segment; since that page holds a different number of items
2471  * than other pages, we need to do it differently.
2472  */
2473  if (offset + MAX_MEMBERS_IN_LAST_MEMBERS_PAGE < offset)
2474  {
2475  /*
2476  * This is the last page of the last segment; we can compute the
2477  * number of items left to allocate in it without modulo
2478  * arithmetic.
2479  */
2480  difference = MaxMultiXactOffset - offset + 1;
2481  }
2482  else
2484 
2485  /*
2486  * Advance to next page, taking care to properly handle the wraparound
2487  * case. OK if nmembers goes negative.
2488  */
2489  nmembers -= difference;
2490  offset += difference;
2491  }
2492 }
2493 
2494 /*
2495  * GetOldestMultiXactId
2496  *
2497  * Return the oldest MultiXactId that's still possibly still seen as live by
2498  * any running transaction. Older ones might still exist on disk, but they no
2499  * longer have any running member transaction.
2500  *
2501  * It's not safe to truncate MultiXact SLRU segments on the value returned by
2502  * this function; however, it can be used by a full-table vacuum to set the
2503  * point at which it will be possible to truncate SLRU for that table.
2504  */
2507 {
2508  MultiXactId oldestMXact;
2510  int i;
2511 
2512  /*
2513  * This is the oldest valid value among all the OldestMemberMXactId[] and
2514  * OldestVisibleMXactId[] entries, or nextMXact if none are valid.
2515  */
2516  LWLockAcquire(MultiXactGenLock, LW_SHARED);
2517 
2518  /*
2519  * We have to beware of the possibility that nextMXact is in the
2520  * wrapped-around state. We don't fix the counter itself here, but we
2521  * must be sure to use a valid value in our calculation.
2522  */
2523  nextMXact = MultiXactState->nextMXact;
2524  if (nextMXact < FirstMultiXactId)
2525  nextMXact = FirstMultiXactId;
2526 
2527  oldestMXact = nextMXact;
2528  for (i = 1; i <= MaxOldestSlot; i++)
2529  {
2530  MultiXactId thisoldest;
2531 
2532  thisoldest = OldestMemberMXactId[i];
2533  if (MultiXactIdIsValid(thisoldest) &&
2534  MultiXactIdPrecedes(thisoldest, oldestMXact))
2535  oldestMXact = thisoldest;
2536  thisoldest = OldestVisibleMXactId[i];
2537  if (MultiXactIdIsValid(thisoldest) &&
2538  MultiXactIdPrecedes(thisoldest, oldestMXact))
2539  oldestMXact = thisoldest;
2540  }
2541 
2542  LWLockRelease(MultiXactGenLock);
2543 
2544  return oldestMXact;
2545 }
2546 
2547 /*
2548  * Determine how aggressively we need to vacuum in order to prevent member
2549  * wraparound.
2550  *
2551  * To do so determine what's the oldest member offset and install the limit
2552  * info in MultiXactState, where it can be used to prevent overrun of old data
2553  * in the members SLRU area.
2554  *
2555  * The return value is true if emergency autovacuum is required and false
2556  * otherwise.
2557  */
2558 static bool
2559 SetOffsetVacuumLimit(bool is_startup)
2560 {
2563  MultiXactOffset oldestOffset = 0; /* placate compiler */
2564  MultiXactOffset prevOldestOffset;
2566  bool oldestOffsetKnown = false;
2567  bool prevOldestOffsetKnown;
2569  MultiXactOffset prevOffsetStopLimit;
2570 
2571  /*
2572  * NB: Have to prevent concurrent truncation, we might otherwise try to
2573  * lookup an oldestMulti that's concurrently getting truncated away.
2574  */
2575  LWLockAcquire(MultiXactTruncationLock, LW_SHARED);
2576 
2577  /* Read relevant fields from shared memory. */
2578  LWLockAcquire(MultiXactGenLock, LW_SHARED);
2579  oldestMultiXactId = MultiXactState->oldestMultiXactId;
2580  nextMXact = MultiXactState->nextMXact;
2581  nextOffset = MultiXactState->nextOffset;
2582  prevOldestOffsetKnown = MultiXactState->oldestOffsetKnown;
2583  prevOldestOffset = MultiXactState->oldestOffset;
2584  prevOffsetStopLimit = MultiXactState->offsetStopLimit;
2585  Assert(MultiXactState->finishedStartup);
2586  LWLockRelease(MultiXactGenLock);
2587 
2588  /*
2589  * Determine the offset of the oldest multixact. Normally, we can read
2590  * the offset from the multixact itself, but there's an important special
2591  * case: if there are no multixacts in existence at all, oldestMXact
2592  * obviously can't point to one. It will instead point to the multixact
2593  * ID that will be assigned the next time one is needed.
2594  */
2595  if (oldestMultiXactId == nextMXact)
2596  {
2597  /*
2598  * When the next multixact gets created, it will be stored at the next
2599  * offset.
2600  */
2601  oldestOffset = nextOffset;
2602  oldestOffsetKnown = true;
2603  }
2604  else
2605  {
2606  /*
2607  * Figure out where the oldest existing multixact's offsets are
2608  * stored. Due to bugs in early release of PostgreSQL 9.3.X and 9.4.X,
2609  * the supposedly-earliest multixact might not really exist. We are
2610  * careful not to fail in that case.
2611  */
2612  oldestOffsetKnown =
2613  find_multixact_start(oldestMultiXactId, &oldestOffset);
2614 
2615  if (oldestOffsetKnown)
2616  ereport(DEBUG1,
2617  (errmsg_internal("oldest MultiXactId member is at offset %u",
2618  oldestOffset)));
2619  else
2620  ereport(LOG,
2621  (errmsg("MultiXact member wraparound protections are disabled because oldest checkpointed MultiXact %u does not exist on disk",
2622  oldestMultiXactId)));
2623  }
2624 
2625  LWLockRelease(MultiXactTruncationLock);
2626 
2627  /*
2628  * If we can, compute limits (and install them MultiXactState) to prevent
2629  * overrun of old data in the members SLRU area. We can only do so if the
2630  * oldest offset is known though.
2631  */
2632  if (oldestOffsetKnown)
2633  {
2634  /* move back to start of the corresponding segment */
2635  offsetStopLimit = oldestOffset - (oldestOffset %
2637 
2638  /* always leave one segment before the wraparound point */
2639  offsetStopLimit -= (MULTIXACT_MEMBERS_PER_PAGE * SLRU_PAGES_PER_SEGMENT);
2640 
2641  if (!prevOldestOffsetKnown && !is_startup)
2642  ereport(LOG,
2643  (errmsg("MultiXact member wraparound protections are now enabled")));
2644 
2645  ereport(DEBUG1,
2646  (errmsg_internal("MultiXact member stop limit is now %u based on MultiXact %u",
2647  offsetStopLimit, oldestMultiXactId)));
2648  }
2649  else if (prevOldestOffsetKnown)
2650  {
2651  /*
2652  * If we failed to get the oldest offset this time, but we have a
2653  * value from a previous pass through this function, use the old
2654  * values rather than automatically forcing an emergency autovacuum
2655  * cycle again.
2656  */
2657  oldestOffset = prevOldestOffset;
2658  oldestOffsetKnown = true;
2659  offsetStopLimit = prevOffsetStopLimit;
2660  }
2661 
2662  /* Install the computed values */
2663  LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
2664  MultiXactState->oldestOffset = oldestOffset;
2665  MultiXactState->oldestOffsetKnown = oldestOffsetKnown;
2666  MultiXactState->offsetStopLimit = offsetStopLimit;
2667  LWLockRelease(MultiXactGenLock);
2668 
2669  /*
2670  * Do we need an emergency autovacuum? If we're not sure, assume yes.
2671  */
2672  return !oldestOffsetKnown ||
2673  (nextOffset - oldestOffset > MULTIXACT_MEMBER_SAFE_THRESHOLD);
2674 }
2675 
2676 /*
2677  * Return whether adding "distance" to "start" would move past "boundary".
2678  *
2679  * We use this to determine whether the addition is "wrapping around" the
2680  * boundary point, hence the name. The reason we don't want to use the regular
2681  * 2^31-modulo arithmetic here is that we want to be able to use the whole of
2682  * the 2^32-1 space here, allowing for more multixacts than would fit
2683  * otherwise.
2684  */
2685 static bool
2687  uint32 distance)
2688 {
2689  MultiXactOffset finish;
2690 
2691  /*
2692  * Note that offset number 0 is not used (see GetMultiXactIdMembers), so
2693  * if the addition wraps around the UINT_MAX boundary, skip that value.
2694  */
2695  finish = start + distance;
2696  if (finish < start)
2697  finish++;
2698 
2699  /*-----------------------------------------------------------------------
2700  * When the boundary is numerically greater than the starting point, any
2701  * value numerically between the two is not wrapped:
2702  *
2703  * <----S----B---->
2704  * [---) = F wrapped past B (and UINT_MAX)
2705  * [---) = F not wrapped
2706  * [----] = F wrapped past B
2707  *
2708  * When the boundary is numerically less than the starting point (i.e. the
2709  * UINT_MAX wraparound occurs somewhere in between) then all values in
2710  * between are wrapped:
2711  *
2712  * <----B----S---->
2713  * [---) = F not wrapped past B (but wrapped past UINT_MAX)
2714  * [---) = F wrapped past B (and UINT_MAX)
2715  * [----] = F not wrapped
2716  *-----------------------------------------------------------------------
2717  */
2718  if (start < boundary)
2719  return finish >= boundary || finish < start;
2720  else
2721  return finish >= boundary && finish < start;
2722 }
2723 
2724 /*
2725  * Find the starting offset of the given MultiXactId.
2726  *
2727  * Returns false if the file containing the multi does not exist on disk.
2728  * Otherwise, returns true and sets *result to the starting member offset.
2729  *
2730  * This function does not prevent concurrent truncation, so if that's
2731  * required, the caller has to protect against that.
2732  */
2733 static bool
2735 {
2736  MultiXactOffset offset;
2737  int pageno;
2738  int entryno;
2739  int slotno;
2740  MultiXactOffset *offptr;
2741 
2742  Assert(MultiXactState->finishedStartup);
2743 
2744  pageno = MultiXactIdToOffsetPage(multi);
2745  entryno = MultiXactIdToOffsetEntry(multi);
2746 
2747  /*
2748  * Write out dirty data, so PhysicalPageExists can work correctly.
2749  */
2752 
2754  return false;
2755 
2756  /* lock is acquired by SimpleLruReadPage_ReadOnly */
2757  slotno = SimpleLruReadPage_ReadOnly(MultiXactOffsetCtl, pageno, multi);
2758  offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
2759  offptr += entryno;
2760  offset = *offptr;
2761  LWLockRelease(MultiXactOffsetSLRULock);
2762 
2763  *result = offset;
2764  return true;
2765 }
2766 
2767 /*
2768  * Determine how many multixacts, and how many multixact members, currently
2769  * exist. Return false if unable to determine.
2770  */
2771 static bool
2773 {
2777  MultiXactId nextMultiXactId;
2778  bool oldestOffsetKnown;
2779 
2780  LWLockAcquire(MultiXactGenLock, LW_SHARED);
2781  nextOffset = MultiXactState->nextOffset;
2782  oldestMultiXactId = MultiXactState->oldestMultiXactId;
2783  nextMultiXactId = MultiXactState->nextMXact;
2784  oldestOffset = MultiXactState->oldestOffset;
2785  oldestOffsetKnown = MultiXactState->oldestOffsetKnown;
2786  LWLockRelease(MultiXactGenLock);
2787 
2788  if (!oldestOffsetKnown)
2789  return false;
2790 
2791  *members = nextOffset - oldestOffset;
2792  *multixacts = nextMultiXactId - oldestMultiXactId;
2793  return true;
2794 }
2795 
2796 /*
2797  * Multixact members can be removed once the multixacts that refer to them
2798  * are older than every datminmxid. autovacuum_multixact_freeze_max_age and
2799  * vacuum_multixact_freeze_table_age work together to make sure we never have
2800  * too many multixacts; we hope that, at least under normal circumstances,
2801  * this will also be sufficient to keep us from using too many offsets.
2802  * However, if the average multixact has many members, we might exhaust the
2803  * members space while still using few enough members that these limits fail
2804  * to trigger full table scans for relminmxid advancement. At that point,
2805  * we'd have no choice but to start failing multixact-creating operations
2806  * with an error.
2807  *
2808  * To prevent that, if more than a threshold portion of the members space is
2809  * used, we effectively reduce autovacuum_multixact_freeze_max_age and
2810  * to a value just less than the number of multixacts in use. We hope that
2811  * this will quickly trigger autovacuuming on the table or tables with the
2812  * oldest relminmxid, thus allowing datminmxid values to advance and removing
2813  * some members.
2814  *
2815  * As the fraction of the member space currently in use grows, we become
2816  * more aggressive in clamping this value. That not only causes autovacuum
2817  * to ramp up, but also makes any manual vacuums the user issues more
2818  * aggressive. This happens because vacuum_set_xid_limits() clamps the
2819  * freeze table and the minimum freeze age based on the effective
2820  * autovacuum_multixact_freeze_max_age this function returns. In the worst
2821  * case, we'll claim the freeze_max_age to zero, and every vacuum of any
2822  * table will try to freeze every multixact.
2823  *
2824  * It's possible that these thresholds should be user-tunable, but for now
2825  * we keep it simple.
2826  */
2827 int
2829 {
2830  MultiXactOffset members;
2831  uint32 multixacts;
2832  uint32 victim_multixacts;
2833  double fraction;
2834 
2835  /* If we can't determine member space utilization, assume the worst. */
2836  if (!ReadMultiXactCounts(&multixacts, &members))
2837  return 0;
2838 
2839  /* If member space utilization is low, no special action is required. */
2840  if (members <= MULTIXACT_MEMBER_SAFE_THRESHOLD)
2842 
2843  /*
2844  * Compute a target for relminmxid advancement. The number of multixacts
2845  * we try to eliminate from the system is based on how far we are past
2846  * MULTIXACT_MEMBER_SAFE_THRESHOLD.
2847  */
2848  fraction = (double) (members - MULTIXACT_MEMBER_SAFE_THRESHOLD) /
2850  victim_multixacts = multixacts * fraction;
2851 
2852  /* fraction could be > 1.0, but lowest possible freeze age is zero */
2853  if (victim_multixacts > multixacts)
2854  return 0;
2855  return multixacts - victim_multixacts;
2856 }
2857 
2858 typedef struct mxtruncinfo
2859 {
2861 } mxtruncinfo;
2862 
2863 /*
2864  * SlruScanDirectory callback
2865  * This callback determines the earliest existing page number.
2866  */
2867 static bool
2868 SlruScanDirCbFindEarliest(SlruCtl ctl, char *filename, int segpage, void *data)
2869 {
2870  mxtruncinfo *trunc = (mxtruncinfo *) data;
2871 
2872  if (trunc->earliestExistingPage == -1 ||
2873  ctl->PagePrecedes(segpage, trunc->earliestExistingPage))
2874  {
2875  trunc->earliestExistingPage = segpage;
2876  }
2877 
2878  return false; /* keep going */
2879 }
2880 
2881 
2882 /*
2883  * Delete members segments [oldest, newOldest)
2884  *
2885  * The members SLRU can, in contrast to the offsets one, be filled to almost
2886  * the full range at once. This means SimpleLruTruncate() can't trivially be
2887  * used - instead the to-be-deleted range is computed using the offsets
2888  * SLRU. C.f. TruncateMultiXact().
2889  */
2890 static void
2892 {
2893  const int maxsegment = MXOffsetToMemberSegment(MaxMultiXactOffset);
2894  int startsegment = MXOffsetToMemberSegment(oldestOffset);
2895  int endsegment = MXOffsetToMemberSegment(newOldestOffset);
2896  int segment = startsegment;
2897 
2898  /*
2899  * Delete all the segments but the last one. The last segment can still
2900  * contain, possibly partially, valid data.
2901  */
2902  while (segment != endsegment)
2903  {
2904  elog(DEBUG2, "truncating multixact members segment %x", segment);
2906 
2907  /* move to next segment, handling wraparound correctly */
2908  if (segment == maxsegment)
2909  segment = 0;
2910  else
2911  segment += 1;
2912  }
2913 }
2914 
2915 /*
2916  * Delete offsets segments [oldest, newOldest)
2917  */
2918 static void
2920 {
2921  /*
2922  * We step back one multixact to avoid passing a cutoff page that hasn't
2923  * been created yet in the rare case that oldestMulti would be the first
2924  * item on a page and oldestMulti == nextMulti. In that case, if we
2925  * didn't subtract one, we'd trigger SimpleLruTruncate's wraparound
2926  * detection.
2927  */
2929  MultiXactIdToOffsetPage(PreviousMultiXactId(newOldestMulti)));
2930 }
2931 
2932 /*
2933  * Remove all MultiXactOffset and MultiXactMember segments before the oldest
2934  * ones still of interest.
2935  *
2936  * This is only called on a primary as part of vacuum (via
2937  * vac_truncate_clog()). During recovery truncation is done by replaying
2938  * truncation WAL records logged here.
2939  *
2940  * newOldestMulti is the oldest currently required multixact, newOldestMultiDB
2941  * is one of the databases preventing newOldestMulti from increasing.
2942  */
2943 void
2944 TruncateMultiXact(MultiXactId newOldestMulti, Oid newOldestMultiDB)
2945 {
2946  MultiXactId oldestMulti;
2947  MultiXactId nextMulti;
2948  MultiXactOffset newOldestOffset;
2951  mxtruncinfo trunc;
2952  MultiXactId earliest;
2953 
2955  Assert(MultiXactState->finishedStartup);
2956 
2957  /*
2958  * We can only allow one truncation to happen at once. Otherwise parts of
2959  * members might vanish while we're doing lookups or similar. There's no
2960  * need to have an interlock with creating new multis or such, since those
2961  * are constrained by the limits (which only grow, never shrink).
2962  */
2963  LWLockAcquire(MultiXactTruncationLock, LW_EXCLUSIVE);
2964 
2965  LWLockAcquire(MultiXactGenLock, LW_SHARED);
2966  nextMulti = MultiXactState->nextMXact;
2967  nextOffset = MultiXactState->nextOffset;
2968  oldestMulti = MultiXactState->oldestMultiXactId;
2969  LWLockRelease(MultiXactGenLock);
2970  Assert(MultiXactIdIsValid(oldestMulti));
2971 
2972  /*
2973  * Make sure to only attempt truncation if there's values to truncate
2974  * away. In normal processing values shouldn't go backwards, but there's
2975  * some corner cases (due to bugs) where that's possible.
2976  */
2977  if (MultiXactIdPrecedesOrEquals(newOldestMulti, oldestMulti))
2978  {
2979  LWLockRelease(MultiXactTruncationLock);
2980  return;
2981  }
2982 
2983  /*
2984  * Note we can't just plow ahead with the truncation; it's possible that
2985  * there are no segments to truncate, which is a problem because we are
2986  * going to attempt to read the offsets page to determine where to
2987  * truncate the members SLRU. So we first scan the directory to determine
2988  * the earliest offsets page number that we can read without error.
2989  *
2990  * When nextMXact is less than one segment away from multiWrapLimit,
2991  * SlruScanDirCbFindEarliest can find some early segment other than the
2992  * actual earliest. (MultiXactOffsetPagePrecedes(EARLIEST, LATEST)
2993  * returns false, because not all pairs of entries have the same answer.)
2994  * That can also arise when an earlier truncation attempt failed unlink()
2995  * or returned early from this function. The only consequence is
2996  * returning early, which wastes space that we could have liberated.
2997  *
2998  * NB: It's also possible that the page that oldestMulti is on has already
2999  * been truncated away, and we crashed before updating oldestMulti.
3000  */
3001  trunc.earliestExistingPage = -1;
3004  if (earliest < FirstMultiXactId)
3005  earliest = FirstMultiXactId;
3006 
3007  /* If there's nothing to remove, we can bail out early. */
3008  if (MultiXactIdPrecedes(oldestMulti, earliest))
3009  {
3010  LWLockRelease(MultiXactTruncationLock);
3011  return;
3012  }
3013 
3014  /*
3015  * First, compute the safe truncation point for MultiXactMember. This is
3016  * the starting offset of the oldest multixact.
3017  *
3018  * Hopefully, find_multixact_start will always work here, because we've
3019  * already checked that it doesn't precede the earliest MultiXact on disk.
3020  * But if it fails, don't truncate anything, and log a message.
3021  */
3022  if (oldestMulti == nextMulti)
3023  {
3024  /* there are NO MultiXacts */
3025  oldestOffset = nextOffset;
3026  }
3027  else if (!find_multixact_start(oldestMulti, &oldestOffset))
3028  {
3029  ereport(LOG,
3030  (errmsg("oldest MultiXact %u not found, earliest MultiXact %u, skipping truncation",
3031  oldestMulti, earliest)));
3032  LWLockRelease(MultiXactTruncationLock);
3033  return;
3034  }
3035 
3036  /*
3037  * Secondly compute up to where to truncate. Lookup the corresponding
3038  * member offset for newOldestMulti for that.
3039  */
3040  if (newOldestMulti == nextMulti)
3041  {
3042  /* there are NO MultiXacts */
3043  newOldestOffset = nextOffset;
3044  }
3045  else if (!find_multixact_start(newOldestMulti, &newOldestOffset))
3046  {
3047  ereport(LOG,
3048  (errmsg("cannot truncate up to MultiXact %u because it does not exist on disk, skipping truncation",
3049  newOldestMulti)));
3050  LWLockRelease(MultiXactTruncationLock);
3051  return;
3052  }
3053 
3054  elog(DEBUG1, "performing multixact truncation: "
3055  "offsets [%u, %u), offsets segments [%x, %x), "
3056  "members [%u, %u), members segments [%x, %x)",
3057  oldestMulti, newOldestMulti,
3058  MultiXactIdToOffsetSegment(oldestMulti),
3059  MultiXactIdToOffsetSegment(newOldestMulti),
3060  oldestOffset, newOldestOffset,
3061  MXOffsetToMemberSegment(oldestOffset),
3062  MXOffsetToMemberSegment(newOldestOffset));
3063 
3064  /*
3065  * Do truncation, and the WAL logging of the truncation, in a critical
3066  * section. That way offsets/members cannot get out of sync anymore, i.e.
3067  * once consistent the newOldestMulti will always exist in members, even
3068  * if we crashed in the wrong moment.
3069  */
3071 
3072  /*
3073  * Prevent checkpoints from being scheduled concurrently. This is critical
3074  * because otherwise a truncation record might not be replayed after a
3075  * crash/basebackup, even though the state of the data directory would
3076  * require it.
3077  */
3079  MyProc->delayChkpt = true;
3080 
3081  /* WAL log truncation */
3082  WriteMTruncateXlogRec(newOldestMultiDB,
3083  oldestMulti, newOldestMulti,
3084  oldestOffset, newOldestOffset);
3085 
3086  /*
3087  * Update in-memory limits before performing the truncation, while inside
3088  * the critical section: Have to do it before truncation, to prevent
3089  * concurrent lookups of those values. Has to be inside the critical
3090  * section as otherwise a future call to this function would error out,
3091  * while looking up the oldest member in offsets, if our caller crashes
3092  * before updating the limits.
3093  */
3094  LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
3095  MultiXactState->oldestMultiXactId = newOldestMulti;
3096  MultiXactState->oldestMultiXactDB = newOldestMultiDB;
3097  LWLockRelease(MultiXactGenLock);
3098 
3099  /* First truncate members */
3100  PerformMembersTruncation(oldestOffset, newOldestOffset);
3101 
3102  /* Then offsets */
3103  PerformOffsetsTruncation(oldestMulti, newOldestMulti);
3104 
3105  MyProc->delayChkpt = false;
3106 
3107  END_CRIT_SECTION();
3108  LWLockRelease(MultiXactTruncationLock);
3109 }
3110 
3111 /*
3112  * Decide whether a MultiXactOffset page number is "older" for truncation
3113  * purposes. Analogous to CLOGPagePrecedes().
3114  *
3115  * Offsetting the values is optional, because MultiXactIdPrecedes() has
3116  * translational symmetry.
3117  */
3118 static bool
3119 MultiXactOffsetPagePrecedes(int page1, int page2)
3120 {
3121  MultiXactId multi1;
3122  MultiXactId multi2;
3123 
3124  multi1 = ((MultiXactId) page1) * MULTIXACT_OFFSETS_PER_PAGE;
3125  multi1 += FirstMultiXactId + 1;
3126  multi2 = ((MultiXactId) page2) * MULTIXACT_OFFSETS_PER_PAGE;
3127  multi2 += FirstMultiXactId + 1;
3128 
3129  return (MultiXactIdPrecedes(multi1, multi2) &&
3130  MultiXactIdPrecedes(multi1,
3131  multi2 + MULTIXACT_OFFSETS_PER_PAGE - 1));
3132 }
3133 
3134 /*
3135  * Decide whether a MultiXactMember page number is "older" for truncation
3136  * purposes. There is no "invalid offset number" so use the numbers verbatim.
3137  */
3138 static bool
3139 MultiXactMemberPagePrecedes(int page1, int page2)
3140 {
3141  MultiXactOffset offset1;
3142  MultiXactOffset offset2;
3143 
3144  offset1 = ((MultiXactOffset) page1) * MULTIXACT_MEMBERS_PER_PAGE;
3145  offset2 = ((MultiXactOffset) page2) * MULTIXACT_MEMBERS_PER_PAGE;
3146 
3147  return (MultiXactOffsetPrecedes(offset1, offset2) &&
3148  MultiXactOffsetPrecedes(offset1,
3149  offset2 + MULTIXACT_MEMBERS_PER_PAGE - 1));
3150 }
3151 
3152 /*
3153  * Decide which of two MultiXactIds is earlier.
3154  *
3155  * XXX do we need to do something special for InvalidMultiXactId?
3156  * (Doesn't look like it.)
3157  */
3158 bool
3160 {
3161  int32 diff = (int32) (multi1 - multi2);
3162 
3163  return (diff < 0);
3164 }
3165 
3166 /*
3167  * MultiXactIdPrecedesOrEquals -- is multi1 logically <= multi2?
3168  *
3169  * XXX do we need to do something special for InvalidMultiXactId?
3170  * (Doesn't look like it.)
3171  */
3172 bool
3174 {
3175  int32 diff = (int32) (multi1 - multi2);
3176 
3177  return (diff <= 0);
3178 }
3179 
3180 
3181 /*
3182  * Decide which of two offsets is earlier.
3183  */
3184 static bool
3186 {
3187  int32 diff = (int32) (offset1 - offset2);
3188 
3189  return (diff < 0);
3190 }
3191 
3192 /*
3193  * Write an xlog record reflecting the zeroing of either a MEMBERs or
3194  * OFFSETs page (info shows which)
3195  */
3196 static void
3197 WriteMZeroPageXlogRec(int pageno, uint8 info)
3198 {
3199  XLogBeginInsert();
3200  XLogRegisterData((char *) (&pageno), sizeof(int));
3201  (void) XLogInsert(RM_MULTIXACT_ID, info);
3202 }
3203 
3204 /*
3205  * Write a TRUNCATE xlog record
3206  *
3207  * We must flush the xlog record to disk before returning --- see notes in
3208  * TruncateCLOG().
3209  */
3210 static void
3212  MultiXactId startTruncOff, MultiXactId endTruncOff,
3213  MultiXactOffset startTruncMemb, MultiXactOffset endTruncMemb)
3214 {
3215  XLogRecPtr recptr;
3216  xl_multixact_truncate xlrec;
3217 
3218  xlrec.oldestMultiDB = oldestMultiDB;
3219 
3220  xlrec.startTruncOff = startTruncOff;
3221  xlrec.endTruncOff = endTruncOff;
3222 
3223  xlrec.startTruncMemb = startTruncMemb;
3224  xlrec.endTruncMemb = endTruncMemb;
3225 
3226  XLogBeginInsert();
3227  XLogRegisterData((char *) (&xlrec), SizeOfMultiXactTruncate);
3228  recptr = XLogInsert(RM_MULTIXACT_ID, XLOG_MULTIXACT_TRUNCATE_ID);
3229  XLogFlush(recptr);
3230 }
3231 
3232 /*
3233  * MULTIXACT resource manager's routines
3234  */
3235 void
3237 {
3238  uint8 info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
3239 
3240  /* Backup blocks are not used in multixact records */
3241  Assert(!XLogRecHasAnyBlockRefs(record));
3242 
3243  if (info == XLOG_MULTIXACT_ZERO_OFF_PAGE)
3244  {
3245  int pageno;
3246  int slotno;
3247 
3248  memcpy(&pageno, XLogRecGetData(record), sizeof(int));
3249 
3250  LWLockAcquire(MultiXactOffsetSLRULock, LW_EXCLUSIVE);
3251 
3252  slotno = ZeroMultiXactOffsetPage(pageno, false);
3254  Assert(!MultiXactOffsetCtl->shared->page_dirty[slotno]);
3255 
3256  LWLockRelease(MultiXactOffsetSLRULock);
3257  }
3258  else if (info == XLOG_MULTIXACT_ZERO_MEM_PAGE)
3259  {
3260  int pageno;
3261  int slotno;
3262 
3263  memcpy(&pageno, XLogRecGetData(record), sizeof(int));
3264 
3265  LWLockAcquire(MultiXactMemberSLRULock, LW_EXCLUSIVE);
3266 
3267  slotno = ZeroMultiXactMemberPage(pageno, false);
3269  Assert(!MultiXactMemberCtl->shared->page_dirty[slotno]);
3270 
3271  LWLockRelease(MultiXactMemberSLRULock);
3272  }
3273  else if (info == XLOG_MULTIXACT_CREATE_ID)
3274  {
3275  xl_multixact_create *xlrec =
3276  (xl_multixact_create *) XLogRecGetData(record);
3277  TransactionId max_xid;
3278  int i;
3279 
3280  /* Store the data back into the SLRU files */
3281  RecordNewMultiXact(xlrec->mid, xlrec->moff, xlrec->nmembers,
3282  xlrec->members);
3283 
3284  /* Make sure nextMXact/nextOffset are beyond what this record has */
3285  MultiXactAdvanceNextMXact(xlrec->mid + 1,
3286  xlrec->moff + xlrec->nmembers);
3287 
3288  /*
3289  * Make sure nextXid is beyond any XID mentioned in the record. This
3290  * should be unnecessary, since any XID found here ought to have other
3291  * evidence in the XLOG, but let's be safe.
3292  */
3293  max_xid = XLogRecGetXid(record);
3294  for (i = 0; i < xlrec->nmembers; i++)
3295  {
3296  if (TransactionIdPrecedes(max_xid, xlrec->members[i].xid))
3297  max_xid = xlrec->members[i].xid;
3298  }
3299 
3301  }
3302  else if (info == XLOG_MULTIXACT_TRUNCATE_ID)
3303  {
3304  xl_multixact_truncate xlrec;
3305  int pageno;
3306 
3307  memcpy(&xlrec, XLogRecGetData(record),
3309 
3310  elog(DEBUG1, "replaying multixact truncation: "
3311  "offsets [%u, %u), offsets segments [%x, %x), "
3312  "members [%u, %u), members segments [%x, %x)",
3313  xlrec.startTruncOff, xlrec.endTruncOff,
3316  xlrec.startTruncMemb, xlrec.endTruncMemb,
3319 
3320  /* should not be required, but more than cheap enough */
3321  LWLockAcquire(MultiXactTruncationLock, LW_EXCLUSIVE);
3322 
3323  /*
3324  * Advance the horizon values, so they're current at the end of
3325  * recovery.
3326  */
3327  SetMultiXactIdLimit(xlrec.endTruncOff, xlrec.oldestMultiDB, false);
3328 
3330 
3331  /*
3332  * During XLOG replay, latest_page_number isn't necessarily set up
3333  * yet; insert a suitable value to bypass the sanity test in
3334  * SimpleLruTruncate.
3335  */
3336  pageno = MultiXactIdToOffsetPage(xlrec.endTruncOff);
3337  MultiXactOffsetCtl->shared->latest_page_number = pageno;
3339 
3340  LWLockRelease(MultiXactTruncationLock);
3341  }
3342  else
3343  elog(PANIC, "multixact_redo: unknown op code %u", info);
3344 }
3345 
3346 Datum
3348 {
3349  typedef struct
3350  {
3351  MultiXactMember *members;
3352  int nmembers;
3353  int iter;
3354  } mxact;
3356  mxact *multi;
3357  FuncCallContext *funccxt;
3358 
3359  if (mxid < FirstMultiXactId)
3360  ereport(ERROR,
3361  (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
3362  errmsg("invalid MultiXactId: %u", mxid)));
3363 
3364  if (SRF_IS_FIRSTCALL())
3365  {
3366  MemoryContext oldcxt;
3367  TupleDesc tupdesc;
3368 
3369  funccxt = SRF_FIRSTCALL_INIT();
3370  oldcxt = MemoryContextSwitchTo(funccxt->multi_call_memory_ctx);
3371 
3372  multi = palloc(sizeof(mxact));
3373  /* no need to allow for old values here */
3374  multi->nmembers = GetMultiXactIdMembers(mxid, &multi->members, false,
3375  false);
3376  multi->iter = 0;
3377 
3378  tupdesc = CreateTemplateTupleDesc(2);
3379  TupleDescInitEntry(tupdesc, (AttrNumber) 1, "xid",
3380  XIDOID, -1, 0);
3381  TupleDescInitEntry(tupdesc, (AttrNumber) 2, "mode",
3382  TEXTOID, -1, 0);
3383 
3384  funccxt->attinmeta = TupleDescGetAttInMetadata(tupdesc);
3385  funccxt->user_fctx = multi;
3386 
3387  MemoryContextSwitchTo(oldcxt);
3388  }
3389 
3390  funccxt = SRF_PERCALL_SETUP();
3391  multi = (mxact *) funccxt->user_fctx;
3392 
3393  while (multi->iter < multi->nmembers)
3394  {
3395  HeapTuple tuple;
3396  char *values[2];
3397 
3398  values[0] = psprintf("%u", multi->members[multi->iter].xid);
3399  values[1] = mxstatus_to_string(multi->members[multi->iter].status);
3400 
3401  tuple = BuildTupleFromCStrings(funccxt->attinmeta, values);
3402 
3403  multi->iter++;
3404  pfree(values[0]);
3405  SRF_RETURN_NEXT(funccxt, HeapTupleGetDatum(tuple));
3406  }
3407 
3408  SRF_RETURN_DONE(funccxt);
3409 }
3410 
3411 /*
3412  * Entrypoint for sync.c to sync offsets files.
3413  */
3414 int
3415 multixactoffsetssyncfiletag(const FileTag *ftag, char *path)
3416 {
3417  return SlruSyncFileTag(MultiXactOffsetCtl, ftag, path);
3418 }
3419 
3420 /*
3421  * Entrypoint for sync.c to sync members files.
3422  */
3423 int
3424 multixactmemberssyncfiletag(const FileTag *ftag, char *path)
3425 {
3426  return SlruSyncFileTag(MultiXactMemberCtl, ftag, path);
3427 }
#define MaxMultiXactOffset
Definition: multixact.h:30
void TrimMultiXact(void)
Definition: multixact.c:2031
Datum pg_get_multixact_members(PG_FUNCTION_ARGS)
Definition: multixact.c:3347
static SlruCtlData MultiXactMemberCtlData
Definition: multixact.c:188
MultiXactStatus
Definition: multixact.h:41
#define MULTIXACT_MEMBER_DANGER_THRESHOLD
Definition: multixact.c:178
MultiXactId nextMXact
Definition: multixact.c:203
#define AllocSetContextCreate
Definition: memutils.h:173
#define DEBUG1
Definition: elog.h:25
void StartupMultiXact(void)
Definition: multixact.c:2008
int errhint(const char *fmt,...)
Definition: elog.c:1156
BackendId MyBackendId
Definition: globals.c:84
void AtPrepare_MultiXact(void)
Definition: multixact.c:1715
static int32 next
Definition: blutils.c:219
MemoryContext TopTransactionContext
Definition: mcxt.c:53
#define MXOffsetToFlagsBitShift(xid)
Definition: multixact.c:167
static bool SlruScanDirCbFindEarliest(SlruCtl ctl, char *filename, int segpage, void *data)
Definition: multixact.c:2868
uint32 MultiXactOffset
Definition: c.h:599
#define TransactionIdEquals(id1, id2)
Definition: transam.h:43
#define debug_elog4(a, b, c, d)
Definition: multixact.c:335
int SlruSyncFileTag(SlruCtl ctl, const FileTag *ftag, char *path)
Definition: slru.c:1593
uint32 TransactionId
Definition: c.h:587
void AdvanceNextFullTransactionIdPastXid(TransactionId xid)
Definition: varsup.c:277
TupleDesc CreateTemplateTupleDesc(int natts)
Definition: tupdesc.c:45
static void dlist_push_head(dlist_head *head, dlist_node *node)
Definition: ilist.h:300
bool TransactionIdIsCurrentTransactionId(TransactionId xid)
Definition: xact.c:870
#define MaxMultiXactId
Definition: multixact.h:26
static MultiXactId * OldestMemberMXactId
Definition: multixact.c:292
int errmsg_plural(const char *fmt_singular, const char *fmt_plural, unsigned long n,...)
Definition: elog.c:1019
MultiXactMember members[FLEXIBLE_ARRAY_MEMBER]
Definition: multixact.c:318
static int ZeroMultiXactOffsetPage(int pageno, bool writeXlog)
Definition: multixact.c:1931
static dlist_node * dlist_tail_node(dlist_head *head)
Definition: ilist.h:485
PGPROC * MyProc
Definition: proc.c:68
MultiXactOffset nextOffset
Definition: multixact.c:206
bool TransactionIdIsInProgress(TransactionId xid)
Definition: procarray.c:1359
#define SRF_IS_FIRSTCALL()
Definition: funcapi.h:293
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:526
void multixact_redo(XLogReaderState *record)
Definition: multixact.c:3236
char * psprintf(const char *fmt,...)
Definition: psprintf.c:46
#define ALLOCSET_SMALL_SIZES
Definition: memutils.h:205
void SimpleLruTruncate(SlruCtl ctl, int cutoffPage)
Definition: slru.c:1226
static bool MultiXactOffsetPagePrecedes(int page1, int page2)
Definition: multixact.c:3119
#define MULTIXACT_MEMBERS_PER_PAGE
Definition: multixact.c:142
#define END_CRIT_SECTION()
Definition: miscadmin.h:149
void BootStrapMultiXact(void)
Definition: multixact.c:1894
MultiXactId MultiXactIdCreateFromMembers(int nmembers, MultiXactMember *members)
Definition: multixact.c:767
static MemoryContext MemoryContextSwitchTo(MemoryContext context)
Definition: palloc.h:109
unsigned char uint8
Definition: c.h:439
static bool find_multixact_start(MultiXactId multi, MultiXactOffset *result)
Definition: multixact.c:2734
#define PreviousMultiXactId(xid)
Definition: multixact.c:181
#define FLEXIBLE_ARRAY_MEMBER
Definition: c.h:350
static MultiXactId GetNewMultiXactId(int nmembers, MultiXactOffset *offset)
Definition: multixact.c:956
#define XLOG_MULTIXACT_ZERO_MEM_PAGE
Definition: multixact.h:73
#define START_CRIT_SECTION()
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Definition: autovacuum.c:125
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void MultiXactGetCheckptMulti(bool is_shutdown, MultiXactId *nextMulti, MultiXactOffset *nextMultiOffset, MultiXactId *oldestMulti, Oid *oldestMultiDB)
Definition: multixact.c:2133
#define MXOffsetToMemberPage(xid)
Definition: multixact.c:159
bool TransactionIdDidCommit(TransactionId transactionId)
Definition: transam.c:125
static MultiXactId * OldestVisibleMXactId
Definition: multixact.c:293
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#define LOG
Definition: elog.h:26
unsigned int Oid
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Definition: xlog.c:8341
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Definition: multixact.c:1975
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Definition: multixact.c:163
void MultiXactAdvanceNextMXact(MultiXactId minMulti, MultiXactOffset minMultiOffset)
Definition: multixact.c:2362
struct mXactCacheEnt mXactCacheEnt
#define PANIC
Definition: elog.h:50
Size SimpleLruShmemSize(int nslots, int nlsns)
Definition: slru.c:156
#define NUM_MULTIXACTOFFSET_BUFFERS
Definition: multixact.h:33
#define SRF_PERCALL_SETUP()
Definition: funcapi.h:297
void SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns, LWLock *ctllock, const char *subdir, int tranche_id, SyncRequestHandler sync_handler)
Definition: slru.c:187
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Definition: xlog.c:2888
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Definition: globals.c:113
void RegisterTwoPhaseRecord(TwoPhaseRmgrId rmid, uint16 info, const void *data, uint32 len)
Definition: twophase.c:1239
signed int int32
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#define SizeOfMultiXactTruncate
Definition: multixact.h:100
#define MultiXactIdToOffsetEntry(xid)
Definition: multixact.c:113
HeapTuple BuildTupleFromCStrings(AttInMetadata *attinmeta, char **values)
Definition: execTuples.c:2146
#define MultiXactIdToOffsetPage(xid)
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Definition: multixact.c:625
static MultiXactStateData * MultiXactState
Definition: multixact.c:291
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Definition: lwlock.c:1803
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MultiXactId oldestMultiXactId
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MultiXactMember members[FLEXIBLE_ARRAY_MEMBER]
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Definition: xlogreader.h:320
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#define XLOG_MULTIXACT_CREATE_ID
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#define MXOffsetToMemberOffset(xid)
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static int MXactCacheMembers
Definition: multixact.c:323
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Definition: multixact.c:3415
#define MultiXactIdToOffsetSegment(xid)
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AttInMetadata * attinmeta
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static void PerformMembersTruncation(MultiXactOffset oldestOffset, MultiXactOffset newOldestOffset)
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Definition: slru.c:1156
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Definition: multixact.c:230
struct mxtruncinfo mxtruncinfo
#define ISUPDATE_from_mxstatus(status)
Definition: multixact.h:56
static void WriteMTruncateXlogRec(Oid oldestMultiDB, MultiXactId startTruncOff, MultiXactId endTruncOff, MultiXactOffset startTruncMemb, MultiXactOffset endTruncMemb)
Definition: multixact.c:3211
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Definition: multixact.h:28
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Definition: slru.c:626
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Definition: slru.c:614
#define FirstMultiXactId
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Definition: ilist.h:358
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Definition: tupdesc.c:583
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Definition: twophase_rmgr.h:27
#define MULTIXACT_OFFSETS_PER_PAGE
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Definition: xlogreader.h:315
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bool TransactionIdPrecedes(TransactionId id1, TransactionId id2)
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static bool MultiXactMemberPagePrecedes(int page1, int page2)
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#define MultiXactOffsetCtl
Definition: multixact.c:190
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Definition: stringinfo.c:188
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Definition: stringinfo.c:59
#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:386
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Definition: multixact.c:2155
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Definition: xloginsert.c:340
XLogRecPtr XLogInsert(RmgrId rmid, uint8 info)
Definition: xloginsert.c:434
#define XLogRecGetXid(decoder)
Definition: xlogreader.h:317
BackendId TwoPhaseGetDummyBackendId(TransactionId xid, bool lock_held)
Definition: twophase.c:916
MultiXactId GetOldestMultiXactId(void)
Definition: multixact.c:2506
#define XLOG_MULTIXACT_ZERO_OFF_PAGE
Definition: multixact.h:72
uintptr_t Datum
Definition: postgres.h:411
MultiXactOffset oldestOffset
Definition: multixact.c:224
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#define debug_elog3(a, b, c)
Definition: multixact.c:334
Size add_size(Size s1, Size s2)
Definition: shmem.c:502
int BackendId
Definition: backendid.h:21
#define OFFSET_WARN_SEGMENTS
AttInMetadata * TupleDescGetAttInMetadata(TupleDesc tupdesc)
Definition: execTuples.c:2097
static void ExtendMultiXactOffset(MultiXactId multi)
Definition: multixact.c:2404
int SimpleLruReadPage_ReadOnly(SlruCtl ctl, int pageno, TransactionId xid)
Definition: slru.c:495
#define InvalidMultiXactId
Definition: multixact.h:24
dlist_node * cur
Definition: ilist.h:161
MultiXactOffset startTruncMemb
Definition: multixact.h:96
void SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid, bool is_startup)
Definition: multixact.c:2213
static void dlist_init(dlist_head *head)
Definition: ilist.h:278
#define ereport(elevel,...)
Definition: elog.h:157
static bool ReadMultiXactCounts(uint32 *multixacts, MultiXactOffset *members)
Definition: multixact.c:2772
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Definition: xlogutils.c:52
TransactionId MultiXactId
Definition: c.h:597
int errmsg_internal(const char *fmt,...)
Definition: elog.c:996
MultiXactId multiWrapLimit
Definition: multixact.c:231
static SlruCtlData MultiXactOffsetCtlData
Definition: multixact.c:187
MultiXactId mid
Definition: multixact.h:79
uint64 XLogRecPtr
Definition: xlogdefs.h:21
#define Assert(condition)
Definition: c.h:804
#define XLR_INFO_MASK
Definition: xlogrecord.h:62
bool SlruScanDirectory(SlruCtl ctl, SlruScanCallback callback, void *data)
Definition: slru.c:1553
static dlist_head MXactCache
Definition: multixact.c:322
static void MultiXactIdSetOldestVisible(void)
Definition: multixact.c:682
#define XLOG_MULTIXACT_TRUNCATE_ID
Definition: multixact.h:75
MemoryContext multi_call_memory_ctx
Definition: funcapi.h:101
struct MultiXactMember MultiXactMember
size_t Size
Definition: c.h:540
#define MXOffsetToMemberSegment(xid)
Definition: multixact.c:160
int errdetail_plural(const char *fmt_singular, const char *fmt_plural, unsigned long n,...)
Definition: elog.c:1134
void AtEOXact_MultiXact(void)
Definition: multixact.c:1686
void PostPrepare_MultiXact(TransactionId xid)
Definition: multixact.c:1729
MultiXactId startTruncOff
Definition: multixact.h:92
bool LWLockAcquire(LWLock *lock, LWLockMode mode)
Definition: lwlock.c:1199
bool IsTransactionState(void)
Definition: xact.c:372
static void mXactCachePut(MultiXactId multi, int nmembers, MultiXactMember *members)
Definition: multixact.c:1585
bool MultiXactIdPrecedes(MultiXactId multi1, MultiXactId multi2)
Definition: multixact.c:3159
MultiXactId multiWarnLimit
Definition: multixact.c:229
#define HeapTupleGetDatum(tuple)
Definition: funcapi.h:220
Size MultiXactShmemSize(void)
Definition: multixact.c:1827
void multixact_twophase_recover(TransactionId xid, uint16 info, void *recdata, uint32 len)
Definition: multixact.c:1779
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:156
static char * filename
Definition: pg_dumpall.c:92
void * user_fctx
Definition: funcapi.h:82
void * palloc(Size size)
Definition: mcxt.c:1062
int errmsg(const char *fmt,...)
Definition: elog.c:909
char * MemoryContextStrdup(MemoryContext context, const char *string)
Definition: mcxt.c:1286
static int ZeroMultiXactMemberPage(int pageno, bool writeXlog)
Definition: multixact.c:1947
void * MemoryContextAlloc(MemoryContext context, Size size)
Definition: mcxt.c:863
static int mXactCacheGetById(MultiXactId multi, MultiXactMember **members)
Definition: multixact.c:1539
static int mxactMemberComparator(const void *arg1, const void *arg2)
Definition: multixact.c:1467
#define elog(elevel,...)
Definition: elog.h:232
bool MultiXactIdPrecedesOrEquals(MultiXactId multi1, MultiXactId multi2)
Definition: multixact.c:3173
int i
static char * mxstatus_to_string(MultiXactStatus status)
Definition: multixact.c:1632
static MemoryContext MXactContext
Definition: multixact.c:324
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Definition: multixact.c:2860
#define MaxOldestSlot
Definition: multixact.c:288
#define SlruPagePrecedesUnitTests(ctl, per_page)
Definition: slru.h:156
bool(* PagePrecedes)(int, int)
Definition: slru.h:130
#define XLogRecHasAnyBlockRefs(decoder)
Definition: xlogreader.h:322
#define PG_FUNCTION_ARGS
Definition: fmgr.h:193
void SlruDeleteSegment(SlruCtl ctl, int segno)
Definition: slru.c:1327
#define CHECK_FOR_INTERRUPTS()
Definition: miscadmin.h:120
#define MAX_MEMBERS_IN_LAST_MEMBERS_PAGE
Definition: multixact.c:155
void SendPostmasterSignal(PMSignalReason reason)
Definition: pmsignal.c:153
int GetMultiXactIdMembers(MultiXactId multi, MultiXactMember **members, bool from_pgupgrade, bool onlyLock)
Definition: multixact.c:1223
#define SLRU_PAGES_PER_SEGMENT
Definition: slru.h:34
static void RecordNewMultiXact(MultiXactId multi, MultiXactOffset offset, int nmembers, MultiXactMember *members)
Definition: multixact.c:862
struct MultiXactStateData MultiXactStateData
#define qsort(a, b, c, d)
Definition: port.h:505
#define TransactionIdIsValid(xid)
Definition: transam.h:41
MultiXactId endTruncOff
Definition: multixact.h:93
static void PerformOffsetsTruncation(MultiXactId oldestMulti, MultiXactId newOldestMulti)
Definition: multixact.c:2919
static void static void status(const char *fmt,...) pg_attribute_printf(1
Definition: pg_regress.c:229
#define MULTIXACT_MEMBER_SAFE_THRESHOLD
Definition: multixact.c:177
void TruncateMultiXact(MultiXactId newOldestMulti, Oid newOldestMultiDB)
Definition: multixact.c:2944
void XLogBeginInsert(void)
Definition: xloginsert.c:135
#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:551
void ReadMultiXactIdRange(MultiXactId *oldest, MultiXactId *next)
Definition: multixact.c:743
static bool MultiXactOffsetPrecedes(MultiXactOffset offset1, MultiXactOffset offset2)
Definition: multixact.c:3185
int SimpleLruZeroPage(SlruCtl ctl, int pageno)
Definition: slru.c:280
void MultiXactAdvanceOldest(MultiXactId oldestMulti, Oid oldestMultiDB)
Definition: multixact.c:2387
static MultiXactId mXactCacheGetBySet(int nmembers, MultiXactMember *members)
Definition: multixact.c:1497
Definition: sync.h:50
static void ExtendMultiXactMember(MultiXactOffset offset, int nmembers)
Definition: multixact.c:2434
MultiXactId multi
Definition: multixact.c:315
#define offsetof(type, field)
Definition: c.h:727
#define NUM_MULTIXACTMEMBER_BUFFERS
Definition: multixact.h:34
MultiXactId MultiXactIdExpand(MultiXactId multi, TransactionId xid, MultiXactStatus status)
Definition: multixact.c:439
#define SRF_RETURN_DONE(_funcctx)
Definition: funcapi.h:317
int multixactmemberssyncfiletag(const FileTag *ftag, char *path)
Definition: multixact.c:3424
MultiXactId ReadNextMultiXactId(void)
Definition: multixact.c:723
void MultiXactSetNextMXact(MultiXactId nextMulti, MultiXactOffset nextMultiOffset)
Definition: multixact.c:2179
#define SRF_FIRSTCALL_INIT()
Definition: funcapi.h:295