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slot.c
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1 /*-------------------------------------------------------------------------
2  *
3  * slot.c
4  * Replication slot management.
5  *
6  *
7  * Copyright (c) 2012-2017, PostgreSQL Global Development Group
8  *
9  *
10  * IDENTIFICATION
11  * src/backend/replication/slot.c
12  *
13  * NOTES
14  *
15  * Replication slots are used to keep state about replication streams
16  * originating from this cluster. Their primary purpose is to prevent the
17  * premature removal of WAL or of old tuple versions in a manner that would
18  * interfere with replication; they are also useful for monitoring purposes.
19  * Slots need to be permanent (to allow restarts), crash-safe, and allocatable
20  * on standbys (to support cascading setups). The requirement that slots be
21  * usable on standbys precludes storing them in the system catalogs.
22  *
23  * Each replication slot gets its own directory inside the $PGDATA/pg_replslot
24  * directory. Inside that directory the state file will contain the slot's
25  * own data. Additional data can be stored alongside that file if required.
26  * While the server is running, the state data is also cached in memory for
27  * efficiency.
28  *
29  * ReplicationSlotAllocationLock must be taken in exclusive mode to allocate
30  * or free a slot. ReplicationSlotControlLock must be taken in shared mode
31  * to iterate over the slots, and in exclusive mode to change the in_use flag
32  * of a slot. The remaining data in each slot is protected by its mutex.
33  *
34  *-------------------------------------------------------------------------
35  */
36 
37 #include "postgres.h"
38 
39 #include <unistd.h>
40 #include <sys/stat.h>
41 
42 #include "access/transam.h"
43 #include "access/xlog_internal.h"
44 #include "common/string.h"
45 #include "miscadmin.h"
46 #include "pgstat.h"
47 #include "replication/slot.h"
48 #include "storage/fd.h"
49 #include "storage/proc.h"
50 #include "storage/procarray.h"
51 #include "utils/builtins.h"
52 
53 /*
54  * Replication slot on-disk data structure.
55  */
56 typedef struct ReplicationSlotOnDisk
57 {
58  /* first part of this struct needs to be version independent */
59 
60  /* data not covered by checksum */
63 
64  /* data covered by checksum */
67 
68  /*
69  * The actual data in the slot that follows can differ based on the above
70  * 'version'.
71  */
72 
75 
76 /* size of version independent data */
77 #define ReplicationSlotOnDiskConstantSize \
78  offsetof(ReplicationSlotOnDisk, slotdata)
79 /* size of the part of the slot not covered by the checksum */
80 #define SnapBuildOnDiskNotChecksummedSize \
81  offsetof(ReplicationSlotOnDisk, version)
82 /* size of the part covered by the checksum */
83 #define SnapBuildOnDiskChecksummedSize \
84  sizeof(ReplicationSlotOnDisk) - SnapBuildOnDiskNotChecksummedSize
85 /* size of the slot data that is version dependent */
86 #define ReplicationSlotOnDiskV2Size \
87  sizeof(ReplicationSlotOnDisk) - ReplicationSlotOnDiskConstantSize
88 
89 #define SLOT_MAGIC 0x1051CA1 /* format identifier */
90 #define SLOT_VERSION 2 /* version for new files */
91 
92 /* Control array for replication slot management */
94 
95 /* My backend's replication slot in the shared memory array */
97 
98 /* GUCs */
99 int max_replication_slots = 0; /* the maximum number of replication
100  * slots */
101 
102 static void ReplicationSlotDropAcquired(void);
103 static void ReplicationSlotDropPtr(ReplicationSlot *slot);
104 
105 /* internal persistency functions */
106 static void RestoreSlotFromDisk(const char *name);
107 static void CreateSlotOnDisk(ReplicationSlot *slot);
108 static void SaveSlotToPath(ReplicationSlot *slot, const char *path, int elevel);
109 
110 /*
111  * Report shared-memory space needed by ReplicationSlotShmemInit.
112  */
113 Size
115 {
116  Size size = 0;
117 
118  if (max_replication_slots == 0)
119  return size;
120 
121  size = offsetof(ReplicationSlotCtlData, replication_slots);
122  size = add_size(size,
124 
125  return size;
126 }
127 
128 /*
129  * Allocate and initialize walsender-related shared memory.
130  */
131 void
133 {
134  bool found;
135 
136  if (max_replication_slots == 0)
137  return;
138 
139  ReplicationSlotCtl = (ReplicationSlotCtlData *)
140  ShmemInitStruct("ReplicationSlot Ctl", ReplicationSlotsShmemSize(),
141  &found);
142 
144  "replication_slot_io");
145 
146  if (!found)
147  {
148  int i;
149 
150  /* First time through, so initialize */
151  MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
152 
153  for (i = 0; i < max_replication_slots; i++)
154  {
155  ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
156 
157  /* everything else is zeroed by the memset above */
158  SpinLockInit(&slot->mutex);
160  }
161  }
162 }
163 
164 /*
165  * Check whether the passed slot name is valid and report errors at elevel.
166  *
167  * Slot names may consist out of [a-z0-9_]{1,NAMEDATALEN-1} which should allow
168  * the name to be used as a directory name on every supported OS.
169  *
170  * Returns whether the directory name is valid or not if elevel < ERROR.
171  */
172 bool
174 {
175  const char *cp;
176 
177  if (strlen(name) == 0)
178  {
179  ereport(elevel,
180  (errcode(ERRCODE_INVALID_NAME),
181  errmsg("replication slot name \"%s\" is too short",
182  name)));
183  return false;
184  }
185 
186  if (strlen(name) >= NAMEDATALEN)
187  {
188  ereport(elevel,
189  (errcode(ERRCODE_NAME_TOO_LONG),
190  errmsg("replication slot name \"%s\" is too long",
191  name)));
192  return false;
193  }
194 
195  for (cp = name; *cp; cp++)
196  {
197  if (!((*cp >= 'a' && *cp <= 'z')
198  || (*cp >= '0' && *cp <= '9')
199  || (*cp == '_')))
200  {
201  ereport(elevel,
202  (errcode(ERRCODE_INVALID_NAME),
203  errmsg("replication slot name \"%s\" contains invalid character",
204  name),
205  errhint("Replication slot names may only contain lower case letters, numbers, and the underscore character.")));
206  return false;
207  }
208  }
209  return true;
210 }
211 
212 /*
213  * Create a new replication slot and mark it as used by this backend.
214  *
215  * name: Name of the slot
216  * db_specific: logical decoding is db specific; if the slot is going to
217  * be used for that pass true, otherwise false.
218  */
219 void
220 ReplicationSlotCreate(const char *name, bool db_specific,
221  ReplicationSlotPersistency persistency)
222 {
223  ReplicationSlot *slot = NULL;
224  int i;
225 
226  Assert(MyReplicationSlot == NULL);
227 
229 
230  /*
231  * If some other backend ran this code concurrently with us, we'd likely
232  * both allocate the same slot, and that would be bad. We'd also be at
233  * risk of missing a name collision. Also, we don't want to try to create
234  * a new slot while somebody's busy cleaning up an old one, because we
235  * might both be monkeying with the same directory.
236  */
237  LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
238 
239  /*
240  * Check for name collision, and identify an allocatable slot. We need to
241  * hold ReplicationSlotControlLock in shared mode for this, so that nobody
242  * else can change the in_use flags while we're looking at them.
243  */
244  LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
245  for (i = 0; i < max_replication_slots; i++)
246  {
247  ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
248 
249  if (s->in_use && strcmp(name, NameStr(s->data.name)) == 0)
250  ereport(ERROR,
252  errmsg("replication slot \"%s\" already exists", name)));
253  if (!s->in_use && slot == NULL)
254  slot = s;
255  }
256  LWLockRelease(ReplicationSlotControlLock);
257 
258  /* If all slots are in use, we're out of luck. */
259  if (slot == NULL)
260  ereport(ERROR,
261  (errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
262  errmsg("all replication slots are in use"),
263  errhint("Free one or increase max_replication_slots.")));
264 
265  /*
266  * Since this slot is not in use, nobody should be looking at any part of
267  * it other than the in_use field unless they're trying to allocate it.
268  * And since we hold ReplicationSlotAllocationLock, nobody except us can
269  * be doing that. So it's safe to initialize the slot.
270  */
271  Assert(!slot->in_use);
272  Assert(slot->active_pid == 0);
273 
274  /* first initialize persistent data */
275  memset(&slot->data, 0, sizeof(ReplicationSlotPersistentData));
276  StrNCpy(NameStr(slot->data.name), name, NAMEDATALEN);
277  slot->data.database = db_specific ? MyDatabaseId : InvalidOid;
278  slot->data.persistency = persistency;
279 
280  /* and then data only present in shared memory */
281  slot->just_dirtied = false;
282  slot->dirty = false;
289 
290  /*
291  * Create the slot on disk. We haven't actually marked the slot allocated
292  * yet, so no special cleanup is required if this errors out.
293  */
294  CreateSlotOnDisk(slot);
295 
296  /*
297  * We need to briefly prevent any other backend from iterating over the
298  * slots while we flip the in_use flag. We also need to set the active
299  * flag while holding the ControlLock as otherwise a concurrent
300  * SlotAcquire() could acquire the slot as well.
301  */
302  LWLockAcquire(ReplicationSlotControlLock, LW_EXCLUSIVE);
303 
304  slot->in_use = true;
305 
306  /* We can now mark the slot active, and that makes it our slot. */
307  SpinLockAcquire(&slot->mutex);
308  Assert(slot->active_pid == 0);
309  slot->active_pid = MyProcPid;
310  SpinLockRelease(&slot->mutex);
311  MyReplicationSlot = slot;
312 
313  LWLockRelease(ReplicationSlotControlLock);
314 
315  /*
316  * Now that the slot has been marked as in_use and in_active, it's safe to
317  * let somebody else try to allocate a slot.
318  */
319  LWLockRelease(ReplicationSlotAllocationLock);
320 }
321 
322 /*
323  * Find a previously created slot and mark it as used by this backend.
324  */
325 void
327 {
328  ReplicationSlot *slot = NULL;
329  int i;
330  int active_pid = 0; /* Keep compiler quiet */
331 
332  Assert(MyReplicationSlot == NULL);
333 
335 
336  /* Search for the named slot and mark it active if we find it. */
337  LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
338  for (i = 0; i < max_replication_slots; i++)
339  {
340  ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
341 
342  if (s->in_use && strcmp(name, NameStr(s->data.name)) == 0)
343  {
344  SpinLockAcquire(&s->mutex);
345  active_pid = s->active_pid;
346  if (active_pid == 0)
347  active_pid = s->active_pid = MyProcPid;
348  SpinLockRelease(&s->mutex);
349  slot = s;
350  break;
351  }
352  }
353  LWLockRelease(ReplicationSlotControlLock);
354 
355  /* If we did not find the slot or it was already active, error out. */
356  if (slot == NULL)
357  ereport(ERROR,
358  (errcode(ERRCODE_UNDEFINED_OBJECT),
359  errmsg("replication slot \"%s\" does not exist", name)));
360  if (active_pid != MyProcPid)
361  ereport(ERROR,
362  (errcode(ERRCODE_OBJECT_IN_USE),
363  errmsg("replication slot \"%s\" is active for PID %d",
364  name, active_pid)));
365 
366  /* We made this slot active, so it's ours now. */
367  MyReplicationSlot = slot;
368 }
369 
370 /*
371  * Release a replication slot, this or another backend can ReAcquire it
372  * later. Resources this slot requires will be preserved.
373  */
374 void
376 {
378 
379  Assert(slot != NULL && slot->active_pid != 0);
380 
381  if (slot->data.persistency == RS_EPHEMERAL)
382  {
383  /*
384  * Delete the slot. There is no !PANIC case where this is allowed to
385  * fail, all that may happen is an incomplete cleanup of the on-disk
386  * data.
387  */
389  }
390  else if (slot->data.persistency == RS_PERSISTENT)
391  {
392  /*
393  * Mark persistent slot inactive. We're not freeing it, just
394  * disconnecting.
395  */
396  SpinLockAcquire(&slot->mutex);
397  slot->active_pid = 0;
398  SpinLockRelease(&slot->mutex);
399  }
400 
401  MyReplicationSlot = NULL;
402 
403  /* might not have been set when we've been a plain slot */
404  LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
406  LWLockRelease(ProcArrayLock);
407 }
408 
409 /*
410  * Cleanup all temporary slots created in current session.
411  */
412 void
414 {
415  int i;
416 
417  Assert(MyReplicationSlot == NULL);
418 
419  /*
420  * No need for locking as we are only interested in slots active in
421  * current process and those are not touched by other processes.
422  */
423  for (i = 0; i < max_replication_slots; i++)
424  {
425  ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
426 
427  if (s->active_pid == MyProcPid)
428  {
430 
432  }
433  }
434 }
435 
436 /*
437  * Permanently drop replication slot identified by the passed in name.
438  */
439 void
441 {
442  Assert(MyReplicationSlot == NULL);
443 
445 
447 }
448 
449 /*
450  * Permanently drop the currently acquired replication slot.
451  */
452 static void
454 {
456 
457  Assert(MyReplicationSlot != NULL);
458 
459  /* slot isn't acquired anymore */
460  MyReplicationSlot = NULL;
461 
463 }
464 
465 /*
466  * Permanently drop the replication slot which will be released by the point
467  * this function returns.
468  */
469 static void
471 {
472  char path[MAXPGPATH];
473  char tmppath[MAXPGPATH];
474 
475  /*
476  * If some other backend ran this code concurrently with us, we might try
477  * to delete a slot with a certain name while someone else was trying to
478  * create a slot with the same name.
479  */
480  LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
481 
482  /* Generate pathnames. */
483  sprintf(path, "pg_replslot/%s", NameStr(slot->data.name));
484  sprintf(tmppath, "pg_replslot/%s.tmp", NameStr(slot->data.name));
485 
486  /*
487  * Rename the slot directory on disk, so that we'll no longer recognize
488  * this as a valid slot. Note that if this fails, we've got to mark the
489  * slot inactive before bailing out. If we're dropping an ephemeral or
490  * a temporary slot, we better never fail hard as the caller won't expect
491  * the slot to survive and this might get called during error handling.
492  */
493  if (rename(path, tmppath) == 0)
494  {
495  /*
496  * We need to fsync() the directory we just renamed and its parent to
497  * make sure that our changes are on disk in a crash-safe fashion. If
498  * fsync() fails, we can't be sure whether the changes are on disk or
499  * not. For now, we handle that by panicking;
500  * StartupReplicationSlots() will try to straighten it out after
501  * restart.
502  */
504  fsync_fname(tmppath, true);
505  fsync_fname("pg_replslot", true);
507  }
508  else
509  {
510  bool fail_softly = slot->data.persistency != RS_PERSISTENT;
511 
512  SpinLockAcquire(&slot->mutex);
513  slot->active_pid = 0;
514  SpinLockRelease(&slot->mutex);
515 
516  ereport(fail_softly ? WARNING : ERROR,
518  errmsg("could not rename file \"%s\" to \"%s\": %m",
519  path, tmppath)));
520  }
521 
522  /*
523  * The slot is definitely gone. Lock out concurrent scans of the array
524  * long enough to kill it. It's OK to clear the active flag here without
525  * grabbing the mutex because nobody else can be scanning the array here,
526  * and nobody can be attached to this slot and thus access it without
527  * scanning the array.
528  */
529  LWLockAcquire(ReplicationSlotControlLock, LW_EXCLUSIVE);
530  slot->active_pid = 0;
531  slot->in_use = false;
532  LWLockRelease(ReplicationSlotControlLock);
533 
534  /*
535  * Slot is dead and doesn't prevent resource removal anymore, recompute
536  * limits.
537  */
540 
541  /*
542  * If removing the directory fails, the worst thing that will happen is
543  * that the user won't be able to create a new slot with the same name
544  * until the next server restart. We warn about it, but that's all.
545  */
546  if (!rmtree(tmppath, true))
549  errmsg("could not remove directory \"%s\"", tmppath)));
550 
551  /*
552  * We release this at the very end, so that nobody starts trying to create
553  * a slot while we're still cleaning up the detritus of the old one.
554  */
555  LWLockRelease(ReplicationSlotAllocationLock);
556 }
557 
558 /*
559  * Serialize the currently acquired slot's state from memory to disk, thereby
560  * guaranteeing the current state will survive a crash.
561  */
562 void
564 {
565  char path[MAXPGPATH];
566 
567  Assert(MyReplicationSlot != NULL);
568 
569  sprintf(path, "pg_replslot/%s", NameStr(MyReplicationSlot->data.name));
570  SaveSlotToPath(MyReplicationSlot, path, ERROR);
571 }
572 
573 /*
574  * Signal that it would be useful if the currently acquired slot would be
575  * flushed out to disk.
576  *
577  * Note that the actual flush to disk can be delayed for a long time, if
578  * required for correctness explicitly do a ReplicationSlotSave().
579  */
580 void
582 {
584 
585  Assert(MyReplicationSlot != NULL);
586 
587  SpinLockAcquire(&slot->mutex);
588  MyReplicationSlot->just_dirtied = true;
589  MyReplicationSlot->dirty = true;
590  SpinLockRelease(&slot->mutex);
591 }
592 
593 /*
594  * Convert a slot that's marked as RS_EPHEMERAL to a RS_PERSISTENT slot,
595  * guaranteeing it will be there after an eventual crash.
596  */
597 void
599 {
601 
602  Assert(slot != NULL);
604 
605  SpinLockAcquire(&slot->mutex);
607  SpinLockRelease(&slot->mutex);
608 
611 }
612 
613 /*
614  * Compute the oldest xmin across all slots and store it in the ProcArray.
615  */
616 void
618 {
619  int i;
621  TransactionId agg_catalog_xmin = InvalidTransactionId;
622 
623  Assert(ReplicationSlotCtl != NULL);
624 
625  if (!already_locked)
626  LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
627 
628  for (i = 0; i < max_replication_slots; i++)
629  {
630  ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
631  TransactionId effective_xmin;
632  TransactionId effective_catalog_xmin;
633 
634  if (!s->in_use)
635  continue;
636 
637  SpinLockAcquire(&s->mutex);
638  effective_xmin = s->effective_xmin;
639  effective_catalog_xmin = s->effective_catalog_xmin;
640  SpinLockRelease(&s->mutex);
641 
642  /* check the data xmin */
643  if (TransactionIdIsValid(effective_xmin) &&
644  (!TransactionIdIsValid(agg_xmin) ||
645  TransactionIdPrecedes(effective_xmin, agg_xmin)))
646  agg_xmin = effective_xmin;
647 
648  /* check the catalog xmin */
649  if (TransactionIdIsValid(effective_catalog_xmin) &&
650  (!TransactionIdIsValid(agg_catalog_xmin) ||
651  TransactionIdPrecedes(effective_catalog_xmin, agg_catalog_xmin)))
652  agg_catalog_xmin = effective_catalog_xmin;
653  }
654 
655  if (!already_locked)
656  LWLockRelease(ReplicationSlotControlLock);
657 
658  ProcArraySetReplicationSlotXmin(agg_xmin, agg_catalog_xmin, already_locked);
659 }
660 
661 /*
662  * Compute the oldest restart LSN across all slots and inform xlog module.
663  */
664 void
666 {
667  int i;
668  XLogRecPtr min_required = InvalidXLogRecPtr;
669 
670  Assert(ReplicationSlotCtl != NULL);
671 
672  LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
673  for (i = 0; i < max_replication_slots; i++)
674  {
675  ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
676  XLogRecPtr restart_lsn;
677 
678  if (!s->in_use)
679  continue;
680 
681  SpinLockAcquire(&s->mutex);
682  restart_lsn = s->data.restart_lsn;
683  SpinLockRelease(&s->mutex);
684 
685  if (restart_lsn != InvalidXLogRecPtr &&
686  (min_required == InvalidXLogRecPtr ||
687  restart_lsn < min_required))
688  min_required = restart_lsn;
689  }
690  LWLockRelease(ReplicationSlotControlLock);
691 
692  XLogSetReplicationSlotMinimumLSN(min_required);
693 }
694 
695 /*
696  * Compute the oldest WAL LSN required by *logical* decoding slots..
697  *
698  * Returns InvalidXLogRecPtr if logical decoding is disabled or no logical
699  * slots exist.
700  *
701  * NB: this returns a value >= ReplicationSlotsComputeRequiredLSN(), since it
702  * ignores physical replication slots.
703  *
704  * The results aren't required frequently, so we don't maintain a precomputed
705  * value like we do for ComputeRequiredLSN() and ComputeRequiredXmin().
706  */
709 {
711  int i;
712 
713  if (max_replication_slots <= 0)
714  return InvalidXLogRecPtr;
715 
716  LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
717 
718  for (i = 0; i < max_replication_slots; i++)
719  {
720  ReplicationSlot *s;
721  XLogRecPtr restart_lsn;
722 
723  s = &ReplicationSlotCtl->replication_slots[i];
724 
725  /* cannot change while ReplicationSlotCtlLock is held */
726  if (!s->in_use)
727  continue;
728 
729  /* we're only interested in logical slots */
730  if (!SlotIsLogical(s))
731  continue;
732 
733  /* read once, it's ok if it increases while we're checking */
734  SpinLockAcquire(&s->mutex);
735  restart_lsn = s->data.restart_lsn;
736  SpinLockRelease(&s->mutex);
737 
738  if (result == InvalidXLogRecPtr ||
739  restart_lsn < result)
740  result = restart_lsn;
741  }
742 
743  LWLockRelease(ReplicationSlotControlLock);
744 
745  return result;
746 }
747 
748 /*
749  * ReplicationSlotsCountDBSlots -- count the number of slots that refer to the
750  * passed database oid.
751  *
752  * Returns true if there are any slots referencing the database. *nslots will
753  * be set to the absolute number of slots in the database, *nactive to ones
754  * currently active.
755  */
756 bool
757 ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
758 {
759  int i;
760 
761  *nslots = *nactive = 0;
762 
763  if (max_replication_slots <= 0)
764  return false;
765 
766  LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
767  for (i = 0; i < max_replication_slots; i++)
768  {
769  ReplicationSlot *s;
770 
771  s = &ReplicationSlotCtl->replication_slots[i];
772 
773  /* cannot change while ReplicationSlotCtlLock is held */
774  if (!s->in_use)
775  continue;
776 
777  /* only logical slots are database specific, skip */
778  if (!SlotIsLogical(s))
779  continue;
780 
781  /* not our database, skip */
782  if (s->data.database != dboid)
783  continue;
784 
785  /* count slots with spinlock held */
786  SpinLockAcquire(&s->mutex);
787  (*nslots)++;
788  if (s->active_pid != 0)
789  (*nactive)++;
790  SpinLockRelease(&s->mutex);
791  }
792  LWLockRelease(ReplicationSlotControlLock);
793 
794  if (*nslots > 0)
795  return true;
796  return false;
797 }
798 
799 /*
800  * ReplicationSlotsDropDBSlots -- Drop all db-specific slots relating to the
801  * passed database oid. The caller should hold an exclusive lock on the
802  * pg_database oid for the database to prevent creation of new slots on the db
803  * or replay from existing slots.
804  *
805  * This routine isn't as efficient as it could be - but we don't drop databases
806  * often, especially databases with lots of slots.
807  *
808  * Another session that concurrently acquires an existing slot on the target DB
809  * (most likely to drop it) may cause this function to ERROR. If that happens
810  * it may have dropped some but not all slots.
811  */
812 void
814 {
815  int i;
816 
817  if (max_replication_slots <= 0)
818  return;
819 
820 restart:
821  LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
822  for (i = 0; i < max_replication_slots; i++)
823  {
824  ReplicationSlot *s;
825  NameData slotname;
826  int active_pid;
827 
828  s = &ReplicationSlotCtl->replication_slots[i];
829 
830  /* cannot change while ReplicationSlotCtlLock is held */
831  if (!s->in_use)
832  continue;
833 
834  /* only logical slots are database specific, skip */
835  if (!SlotIsLogical(s))
836  continue;
837 
838  /* not our database, skip */
839  if (s->data.database != dboid)
840  continue;
841 
842  /* Claim the slot, as if ReplicationSlotAcquire()ing. */
843  SpinLockAcquire(&s->mutex);
844  strncpy(NameStr(slotname), NameStr(s->data.name), NAMEDATALEN);
845  NameStr(slotname)[NAMEDATALEN-1] = '\0';
846  active_pid = s->active_pid;
847  if (active_pid == 0)
848  {
849  MyReplicationSlot = s;
850  s->active_pid = MyProcPid;
851  }
852  SpinLockRelease(&s->mutex);
853 
854  /*
855  * We might fail here if the slot was active. Even though we hold an
856  * exclusive lock on the database object a logical slot for that DB can
857  * still be active if it's being dropped by a backend connected to
858  * another DB or is otherwise acquired.
859  *
860  * It's an unlikely race that'll only arise from concurrent user action,
861  * so we'll just bail out.
862  */
863  if (active_pid)
864  elog(ERROR, "replication slot %s is in use by pid %d",
865  NameStr(slotname), active_pid);
866 
867  /*
868  * To avoid largely duplicating ReplicationSlotDropAcquired() or
869  * complicating it with already_locked flags for ProcArrayLock,
870  * ReplicationSlotControlLock and ReplicationSlotAllocationLock, we
871  * just release our ReplicationSlotControlLock to drop the slot.
872  *
873  * For safety we'll restart our scan from the beginning each
874  * time we release the lock.
875  */
876  LWLockRelease(ReplicationSlotControlLock);
878  goto restart;
879  }
880  LWLockRelease(ReplicationSlotControlLock);
881 
882  /* recompute limits once after all slots are dropped */
885 }
886 
887 
888 /*
889  * Check whether the server's configuration supports using replication
890  * slots.
891  */
892 void
894 {
895  if (max_replication_slots == 0)
896  ereport(ERROR,
897  (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
898  (errmsg("replication slots can only be used if max_replication_slots > 0"))));
899 
901  ereport(ERROR,
902  (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
903  errmsg("replication slots can only be used if wal_level >= replica")));
904 }
905 
906 /*
907  * Reserve WAL for the currently active slot.
908  *
909  * Compute and set restart_lsn in a manner that's appropriate for the type of
910  * the slot and concurrency safe.
911  */
912 void
914 {
916 
917  Assert(slot != NULL);
919 
920  /*
921  * The replication slot mechanism is used to prevent removal of required
922  * WAL. As there is no interlock between this routine and checkpoints, WAL
923  * segments could concurrently be removed when a now stale return value of
924  * ReplicationSlotsComputeRequiredLSN() is used. In the unlikely case that
925  * this happens we'll just retry.
926  */
927  while (true)
928  {
929  XLogSegNo segno;
930 
931  /*
932  * For logical slots log a standby snapshot and start logical decoding
933  * at exactly that position. That allows the slot to start up more
934  * quickly.
935  *
936  * That's not needed (or indeed helpful) for physical slots as they'll
937  * start replay at the last logged checkpoint anyway. Instead return
938  * the location of the last redo LSN. While that slightly increases
939  * the chance that we have to retry, it's where a base backup has to
940  * start replay at.
941  */
942  if (!RecoveryInProgress() && SlotIsLogical(slot))
943  {
944  XLogRecPtr flushptr;
945 
946  /* start at current insert position */
948 
949  /* make sure we have enough information to start */
950  flushptr = LogStandbySnapshot();
951 
952  /* and make sure it's fsynced to disk */
953  XLogFlush(flushptr);
954  }
955  else
956  {
957  slot->data.restart_lsn = GetRedoRecPtr();
958  }
959 
960  /* prevent WAL removal as fast as possible */
962 
963  /*
964  * If all required WAL is still there, great, otherwise retry. The
965  * slot should prevent further removal of WAL, unless there's a
966  * concurrent ReplicationSlotsComputeRequiredLSN() after we've written
967  * the new restart_lsn above, so normally we should never need to loop
968  * more than twice.
969  */
970  XLByteToSeg(slot->data.restart_lsn, segno);
971  if (XLogGetLastRemovedSegno() < segno)
972  break;
973  }
974 }
975 
976 /*
977  * Flush all replication slots to disk.
978  *
979  * This needn't actually be part of a checkpoint, but it's a convenient
980  * location.
981  */
982 void
984 {
985  int i;
986 
987  elog(DEBUG1, "performing replication slot checkpoint");
988 
989  /*
990  * Prevent any slot from being created/dropped while we're active. As we
991  * explicitly do *not* want to block iterating over replication_slots or
992  * acquiring a slot we cannot take the control lock - but that's OK,
993  * because holding ReplicationSlotAllocationLock is strictly stronger, and
994  * enough to guarantee that nobody can change the in_use bits on us.
995  */
996  LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
997 
998  for (i = 0; i < max_replication_slots; i++)
999  {
1000  ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
1001  char path[MAXPGPATH];
1002 
1003  if (!s->in_use)
1004  continue;
1005 
1006  /* save the slot to disk, locking is handled in SaveSlotToPath() */
1007  sprintf(path, "pg_replslot/%s", NameStr(s->data.name));
1008  SaveSlotToPath(s, path, LOG);
1009  }
1010  LWLockRelease(ReplicationSlotAllocationLock);
1011 }
1012 
1013 /*
1014  * Load all replication slots from disk into memory at server startup. This
1015  * needs to be run before we start crash recovery.
1016  */
1017 void
1019 {
1020  DIR *replication_dir;
1021  struct dirent *replication_de;
1022 
1023  elog(DEBUG1, "starting up replication slots");
1024 
1025  /* restore all slots by iterating over all on-disk entries */
1026  replication_dir = AllocateDir("pg_replslot");
1027  while ((replication_de = ReadDir(replication_dir, "pg_replslot")) != NULL)
1028  {
1029  struct stat statbuf;
1030  char path[MAXPGPATH];
1031 
1032  if (strcmp(replication_de->d_name, ".") == 0 ||
1033  strcmp(replication_de->d_name, "..") == 0)
1034  continue;
1035 
1036  snprintf(path, MAXPGPATH, "pg_replslot/%s", replication_de->d_name);
1037 
1038  /* we're only creating directories here, skip if it's not our's */
1039  if (lstat(path, &statbuf) == 0 && !S_ISDIR(statbuf.st_mode))
1040  continue;
1041 
1042  /* we crashed while a slot was being setup or deleted, clean up */
1043  if (pg_str_endswith(replication_de->d_name, ".tmp"))
1044  {
1045  if (!rmtree(path, true))
1046  {
1047  ereport(WARNING,
1049  errmsg("could not remove directory \"%s\"", path)));
1050  continue;
1051  }
1052  fsync_fname("pg_replslot", true);
1053  continue;
1054  }
1055 
1056  /* looks like a slot in a normal state, restore */
1057  RestoreSlotFromDisk(replication_de->d_name);
1058  }
1059  FreeDir(replication_dir);
1060 
1061  /* currently no slots exist, we're done. */
1062  if (max_replication_slots <= 0)
1063  return;
1064 
1065  /* Now that we have recovered all the data, compute replication xmin */
1068 }
1069 
1070 /* ----
1071  * Manipulation of on-disk state of replication slots
1072  *
1073  * NB: none of the routines below should take any notice whether a slot is the
1074  * current one or not, that's all handled a layer above.
1075  * ----
1076  */
1077 static void
1079 {
1080  char tmppath[MAXPGPATH];
1081  char path[MAXPGPATH];
1082  struct stat st;
1083 
1084  /*
1085  * No need to take out the io_in_progress_lock, nobody else can see this
1086  * slot yet, so nobody else will write. We're reusing SaveSlotToPath which
1087  * takes out the lock, if we'd take the lock here, we'd deadlock.
1088  */
1089 
1090  sprintf(path, "pg_replslot/%s", NameStr(slot->data.name));
1091  sprintf(tmppath, "pg_replslot/%s.tmp", NameStr(slot->data.name));
1092 
1093  /*
1094  * It's just barely possible that some previous effort to create or drop a
1095  * slot with this name left a temp directory lying around. If that seems
1096  * to be the case, try to remove it. If the rmtree() fails, we'll error
1097  * out at the mkdir() below, so we don't bother checking success.
1098  */
1099  if (stat(tmppath, &st) == 0 && S_ISDIR(st.st_mode))
1100  rmtree(tmppath, true);
1101 
1102  /* Create and fsync the temporary slot directory. */
1103  if (mkdir(tmppath, S_IRWXU) < 0)
1104  ereport(ERROR,
1106  errmsg("could not create directory \"%s\": %m",
1107  tmppath)));
1108  fsync_fname(tmppath, true);
1109 
1110  /* Write the actual state file. */
1111  slot->dirty = true; /* signal that we really need to write */
1112  SaveSlotToPath(slot, tmppath, ERROR);
1113 
1114  /* Rename the directory into place. */
1115  if (rename(tmppath, path) != 0)
1116  ereport(ERROR,
1118  errmsg("could not rename file \"%s\" to \"%s\": %m",
1119  tmppath, path)));
1120 
1121  /*
1122  * If we'd now fail - really unlikely - we wouldn't know whether this slot
1123  * would persist after an OS crash or not - so, force a restart. The
1124  * restart would try to fsync this again till it works.
1125  */
1127 
1128  fsync_fname(path, true);
1129  fsync_fname("pg_replslot", true);
1130 
1131  END_CRIT_SECTION();
1132 }
1133 
1134 /*
1135  * Shared functionality between saving and creating a replication slot.
1136  */
1137 static void
1138 SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel)
1139 {
1140  char tmppath[MAXPGPATH];
1141  char path[MAXPGPATH];
1142  int fd;
1144  bool was_dirty;
1145 
1146  /* first check whether there's something to write out */
1147  SpinLockAcquire(&slot->mutex);
1148  was_dirty = slot->dirty;
1149  slot->just_dirtied = false;
1150  SpinLockRelease(&slot->mutex);
1151 
1152  /* and don't do anything if there's nothing to write */
1153  if (!was_dirty)
1154  return;
1155 
1157 
1158  /* silence valgrind :( */
1159  memset(&cp, 0, sizeof(ReplicationSlotOnDisk));
1160 
1161  sprintf(tmppath, "%s/state.tmp", dir);
1162  sprintf(path, "%s/state", dir);
1163 
1164  fd = OpenTransientFile(tmppath,
1165  O_CREAT | O_EXCL | O_WRONLY | PG_BINARY,
1166  S_IRUSR | S_IWUSR);
1167  if (fd < 0)
1168  {
1169  ereport(elevel,
1171  errmsg("could not create file \"%s\": %m",
1172  tmppath)));
1173  return;
1174  }
1175 
1176  cp.magic = SLOT_MAGIC;
1177  INIT_CRC32C(cp.checksum);
1178  cp.version = SLOT_VERSION;
1180 
1181  SpinLockAcquire(&slot->mutex);
1182 
1183  memcpy(&cp.slotdata, &slot->data, sizeof(ReplicationSlotPersistentData));
1184 
1185  SpinLockRelease(&slot->mutex);
1186 
1187  COMP_CRC32C(cp.checksum,
1188  (char *) (&cp) + SnapBuildOnDiskNotChecksummedSize,
1190  FIN_CRC32C(cp.checksum);
1191 
1193  if ((write(fd, &cp, sizeof(cp))) != sizeof(cp))
1194  {
1195  int save_errno = errno;
1196 
1198  CloseTransientFile(fd);
1199  errno = save_errno;
1200  ereport(elevel,
1202  errmsg("could not write to file \"%s\": %m",
1203  tmppath)));
1204  return;
1205  }
1207 
1208  /* fsync the temporary file */
1210  if (pg_fsync(fd) != 0)
1211  {
1212  int save_errno = errno;
1213 
1215  CloseTransientFile(fd);
1216  errno = save_errno;
1217  ereport(elevel,
1219  errmsg("could not fsync file \"%s\": %m",
1220  tmppath)));
1221  return;
1222  }
1224 
1225  CloseTransientFile(fd);
1226 
1227  /* rename to permanent file, fsync file and directory */
1228  if (rename(tmppath, path) != 0)
1229  {
1230  ereport(elevel,
1232  errmsg("could not rename file \"%s\" to \"%s\": %m",
1233  tmppath, path)));
1234  return;
1235  }
1236 
1237  /* Check CreateSlot() for the reasoning of using a crit. section. */
1239 
1240  fsync_fname(path, false);
1241  fsync_fname(dir, true);
1242  fsync_fname("pg_replslot", true);
1243 
1244  END_CRIT_SECTION();
1245 
1246  /*
1247  * Successfully wrote, unset dirty bit, unless somebody dirtied again
1248  * already.
1249  */
1250  SpinLockAcquire(&slot->mutex);
1251  if (!slot->just_dirtied)
1252  slot->dirty = false;
1253  SpinLockRelease(&slot->mutex);
1254 
1256 }
1257 
1258 /*
1259  * Load a single slot from disk into memory.
1260  */
1261 static void
1263 {
1265  int i;
1266  char path[MAXPGPATH];
1267  int fd;
1268  bool restored = false;
1269  int readBytes;
1270  pg_crc32c checksum;
1271 
1272  /* no need to lock here, no concurrent access allowed yet */
1273 
1274  /* delete temp file if it exists */
1275  sprintf(path, "pg_replslot/%s/state.tmp", name);
1276  if (unlink(path) < 0 && errno != ENOENT)
1277  ereport(PANIC,
1279  errmsg("could not remove file \"%s\": %m", path)));
1280 
1281  sprintf(path, "pg_replslot/%s/state", name);
1282 
1283  elog(DEBUG1, "restoring replication slot from \"%s\"", path);
1284 
1285  fd = OpenTransientFile(path, O_RDWR | PG_BINARY, 0);
1286 
1287  /*
1288  * We do not need to handle this as we are rename()ing the directory into
1289  * place only after we fsync()ed the state file.
1290  */
1291  if (fd < 0)
1292  ereport(PANIC,
1294  errmsg("could not open file \"%s\": %m", path)));
1295 
1296  /*
1297  * Sync state file before we're reading from it. We might have crashed
1298  * while it wasn't synced yet and we shouldn't continue on that basis.
1299  */
1301  if (pg_fsync(fd) != 0)
1302  {
1303  CloseTransientFile(fd);
1304  ereport(PANIC,
1306  errmsg("could not fsync file \"%s\": %m",
1307  path)));
1308  }
1310 
1311  /* Also sync the parent directory */
1313  fsync_fname(path, true);
1314  END_CRIT_SECTION();
1315 
1316  /* read part of statefile that's guaranteed to be version independent */
1318  readBytes = read(fd, &cp, ReplicationSlotOnDiskConstantSize);
1320  if (readBytes != ReplicationSlotOnDiskConstantSize)
1321  {
1322  int saved_errno = errno;
1323 
1324  CloseTransientFile(fd);
1325  errno = saved_errno;
1326  ereport(PANIC,
1328  errmsg("could not read file \"%s\", read %d of %u: %m",
1329  path, readBytes,
1331  }
1332 
1333  /* verify magic */
1334  if (cp.magic != SLOT_MAGIC)
1335  ereport(PANIC,
1337  errmsg("replication slot file \"%s\" has wrong magic number: %u instead of %u",
1338  path, cp.magic, SLOT_MAGIC)));
1339 
1340  /* verify version */
1341  if (cp.version != SLOT_VERSION)
1342  ereport(PANIC,
1344  errmsg("replication slot file \"%s\" has unsupported version %u",
1345  path, cp.version)));
1346 
1347  /* boundary check on length */
1349  ereport(PANIC,
1351  errmsg("replication slot file \"%s\" has corrupted length %u",
1352  path, cp.length)));
1353 
1354  /* Now that we know the size, read the entire file */
1356  readBytes = read(fd,
1357  (char *) &cp + ReplicationSlotOnDiskConstantSize,
1358  cp.length);
1360  if (readBytes != cp.length)
1361  {
1362  int saved_errno = errno;
1363 
1364  CloseTransientFile(fd);
1365  errno = saved_errno;
1366  ereport(PANIC,
1368  errmsg("could not read file \"%s\", read %d of %u: %m",
1369  path, readBytes, cp.length)));
1370  }
1371 
1372  CloseTransientFile(fd);
1373 
1374  /* now verify the CRC */
1375  INIT_CRC32C(checksum);
1376  COMP_CRC32C(checksum,
1377  (char *) &cp + SnapBuildOnDiskNotChecksummedSize,
1379  FIN_CRC32C(checksum);
1380 
1381  if (!EQ_CRC32C(checksum, cp.checksum))
1382  ereport(PANIC,
1383  (errmsg("checksum mismatch for replication slot file \"%s\": is %u, should be %u",
1384  path, checksum, cp.checksum)));
1385 
1386  /*
1387  * If we crashed with an ephemeral slot active, don't restore but delete
1388  * it.
1389  */
1391  {
1392  sprintf(path, "pg_replslot/%s", name);
1393 
1394  if (!rmtree(path, true))
1395  {
1396  ereport(WARNING,
1398  errmsg("could not remove directory \"%s\"", path)));
1399  }
1400  fsync_fname("pg_replslot", true);
1401  return;
1402  }
1403 
1404  /* nothing can be active yet, don't lock anything */
1405  for (i = 0; i < max_replication_slots; i++)
1406  {
1407  ReplicationSlot *slot;
1408 
1409  slot = &ReplicationSlotCtl->replication_slots[i];
1410 
1411  if (slot->in_use)
1412  continue;
1413 
1414  /* restore the entire set of persistent data */
1415  memcpy(&slot->data, &cp.slotdata,
1417 
1418  /* initialize in memory state */
1419  slot->effective_xmin = cp.slotdata.xmin;
1421 
1426 
1427  slot->in_use = true;
1428  slot->active_pid = 0;
1429 
1430  restored = true;
1431  break;
1432  }
1433 
1434  if (!restored)
1435  ereport(PANIC,
1436  (errmsg("too many replication slots active before shutdown"),
1437  errhint("Increase max_replication_slots and try again.")));
1438 }
#define INIT_CRC32C(crc)
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XLogRecPtr ReplicationSlotsComputeLogicalRestartLSN(void)
Definition: slot.c:708
TransactionId catalog_xmin
Definition: slot.h:65
#define InvalidTransactionId
Definition: transam.h:31
unsigned int uint32
Definition: c.h:268
DIR * AllocateDir(const char *dirname)
Definition: fd.c:2335
void ReplicationSlotRelease(void)
Definition: slot.c:375
static void pgstat_report_wait_end(void)
Definition: pgstat.h:1231
TransactionId xmin
Definition: slot.h:57
#define EQ_CRC32C(c1, c2)
Definition: pg_crc32c.h:42
#define SlotIsLogical(slot)
Definition: slot.h:134
int unlink(const char *filename)
#define ereport(elevel, rest)
Definition: elog.h:122
bool TransactionIdPrecedes(TransactionId id1, TransactionId id2)
Definition: transam.c:300
pg_crc32c checksum
Definition: slot.c:62
struct ReplicationSlotOnDisk ReplicationSlotOnDisk
void LWLockInitialize(LWLock *lock, int tranche_id)
Definition: lwlock.c:667
int CloseTransientFile(int fd)
Definition: fd.c:2305
#define WARNING
Definition: elog.h:40
bool rmtree(const char *path, bool rmtopdir)
Definition: rmtree.c:36
bool in_use
Definition: slot.h:91
static int elevel
Definition: vacuumlazy.c:137
#define SpinLockRelease(lock)
Definition: spin.h:64
Size mul_size(Size s1, Size s2)
Definition: shmem.c:492
bool just_dirtied
Definition: slot.h:97
Size add_size(Size s1, Size s2)
Definition: shmem.c:475
TransactionId effective_catalog_xmin
Definition: slot.h:112
Oid MyDatabaseId
Definition: globals.c:76
#define SLOT_VERSION
Definition: slot.c:90
void ReplicationSlotDrop(const char *name)
Definition: slot.c:440
#define InvalidOid
Definition: postgres_ext.h:36
ReplicationSlot * MyReplicationSlot
Definition: slot.c:96
#define XLByteToSeg(xlrp, logSegNo)
int max_replication_slots
Definition: slot.c:99
#define NULL
Definition: c.h:229
#define ReplicationSlotOnDiskV2Size
Definition: slot.c:86
uint64 XLogRecPtr
Definition: xlogdefs.h:21
#define Assert(condition)
Definition: c.h:675
#define StrNCpy(dst, src, len)
Definition: c.h:830
struct dirent * ReadDir(DIR *dir, const char *dirname)
Definition: fd.c:2401
XLogRecPtr restart_lsn
Definition: slot.h:68
void ReplicationSlotAcquire(const char *name)
Definition: slot.c:326
#define ReplicationSlotOnDiskConstantSize
Definition: slot.c:77
size_t Size
Definition: c.h:356
uint32 version
Definition: slot.c:65
static void pgstat_report_wait_start(uint32 wait_event_info)
Definition: pgstat.h:1207
#define SnapBuildOnDiskChecksummedSize
Definition: slot.c:83
bool LWLockAcquire(LWLock *lock, LWLockMode mode)
Definition: lwlock.c:1111
void LWLockRegisterTranche(int tranche_id, char *tranche_name)
Definition: lwlock.c:592
XLogRecPtr GetRedoRecPtr(void)
Definition: xlog.c:8150
const char * name
Definition: encode.c:521
bool ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
Definition: slot.c:757
XLogRecPtr candidate_xmin_lsn
Definition: slot.h:128
ReplicationSlotPersistency
Definition: slot.h:28
int errmsg(const char *fmt,...)
Definition: elog.c:797
pid_t active_pid
Definition: slot.h:94
int i
#define NameStr(name)
Definition: c.h:499
void ProcArraySetReplicationSlotXmin(TransactionId xmin, TransactionId catalog_xmin, bool already_locked)
Definition: procarray.c:2948
int pg_fsync(int fd)
Definition: fd.c:333
ReplicationSlot replication_slots[1]
Definition: slot.h:145
char d_name[MAX_PATH]
Definition: dirent.h:14
#define elog
Definition: elog.h:219
slock_t mutex
Definition: slot.h:88
#define TransactionIdIsValid(xid)
Definition: transam.h:41
#define COMP_CRC32C(crc, data, len)
Definition: pg_crc32c.h:73
#define ERRCODE_DUPLICATE_OBJECT
Definition: streamutil.c:31
#define lstat(path, sb)
Definition: win32.h:272
void CheckPointReplicationSlots(void)
Definition: slot.c:983
#define FIN_CRC32C(crc)
Definition: pg_crc32c.h:78
void ReplicationSlotsDropDBSlots(Oid dboid)
Definition: slot.c:813
void ReplicationSlotsComputeRequiredXmin(bool already_locked)
Definition: slot.c:617
bool dirty
Definition: slot.h:98
#define read(a, b, c)
Definition: win32.h:18
int FreeDir(DIR *dir)
Definition: fd.c:2444
XLogRecPtr candidate_restart_lsn
Definition: slot.h:130
#define offsetof(type, field)
Definition: c.h:555
void ReplicationSlotMarkDirty(void)
Definition: slot.c:581
LWLock io_in_progress_lock
Definition: slot.h:118