Line data Source code
1 : /*-------------------------------------------------------------------------
2 : * slotsync.c
3 : * Functionality for synchronizing slots to a standby server from the
4 : * primary server.
5 : *
6 : * Copyright (c) 2024-2026, PostgreSQL Global Development Group
7 : *
8 : * IDENTIFICATION
9 : * src/backend/replication/logical/slotsync.c
10 : *
11 : * This file contains the code for slot synchronization on a physical standby
12 : * to fetch logical failover slots information from the primary server, create
13 : * the slots on the standby and synchronize them periodically.
14 : *
15 : * Slot synchronization can be performed either automatically by enabling slot
16 : * sync worker or manually by calling SQL function pg_sync_replication_slots().
17 : *
18 : * If the WAL corresponding to the remote's restart_lsn is not available on the
19 : * physical standby or the remote's catalog_xmin precedes the oldest xid for
20 : * which it is guaranteed that rows wouldn't have been removed then we cannot
21 : * create the local standby slot because that would mean moving the local slot
22 : * backward and decoding won't be possible via such a slot. In this case, the
23 : * slot will be marked as RS_TEMPORARY. Once the primary server catches up,
24 : * the slot will be marked as RS_PERSISTENT (which means sync-ready) after
25 : * which slot sync worker can perform the sync periodically or user can call
26 : * pg_sync_replication_slots() periodically to perform the syncs.
27 : *
28 : * If synchronized slots fail to build a consistent snapshot from the
29 : * restart_lsn before reaching confirmed_flush_lsn, they would become
30 : * unreliable after promotion due to potential data loss from changes
31 : * before reaching a consistent point. This can happen because the slots can
32 : * be synced at some random time and we may not reach the consistent point
33 : * at the same WAL location as the primary. So, we mark such slots as
34 : * RS_TEMPORARY. Once the decoding from corresponding LSNs can reach a
35 : * consistent point, they will be marked as RS_PERSISTENT.
36 : *
37 : * The slot sync worker waits for some time before the next synchronization,
38 : * with the duration varying based on whether any slots were updated during
39 : * the last cycle. Refer to the comments above wait_for_slot_activity() for
40 : * more details.
41 : *
42 : * If the SQL function pg_sync_replication_slots() is used to sync the slots,
43 : * and if the slots are not ready to be synced and are marked as RS_TEMPORARY
44 : * because of any of the reasons mentioned above, then the SQL function also
45 : * waits and retries until the slots are marked as RS_PERSISTENT (which means
46 : * sync-ready). Refer to the comments in SyncReplicationSlots() for more
47 : * details.
48 : *
49 : * Any standby synchronized slots will be dropped if they no longer need
50 : * to be synchronized. See comment atop drop_local_obsolete_slots() for more
51 : * details.
52 : *---------------------------------------------------------------------------
53 : */
54 :
55 : #include "postgres.h"
56 :
57 : #include <time.h>
58 :
59 : #include "access/xlog_internal.h"
60 : #include "access/xlogrecovery.h"
61 : #include "catalog/pg_database.h"
62 : #include "libpq/pqsignal.h"
63 : #include "pgstat.h"
64 : #include "postmaster/interrupt.h"
65 : #include "replication/logical.h"
66 : #include "replication/slotsync.h"
67 : #include "replication/snapbuild.h"
68 : #include "storage/ipc.h"
69 : #include "storage/lmgr.h"
70 : #include "storage/proc.h"
71 : #include "storage/procarray.h"
72 : #include "tcop/tcopprot.h"
73 : #include "utils/builtins.h"
74 : #include "utils/memutils.h"
75 : #include "utils/pg_lsn.h"
76 : #include "utils/ps_status.h"
77 : #include "utils/timeout.h"
78 :
79 : /*
80 : * Struct for sharing information to control slot synchronization.
81 : *
82 : * The 'pid' is either the slot sync worker's pid or the backend's pid running
83 : * the SQL function pg_sync_replication_slots(). When the startup process sets
84 : * 'stopSignaled' during promotion, it uses this 'pid' to wake up the currently
85 : * synchronizing process so that the process can immediately stop its
86 : * synchronizing work on seeing 'stopSignaled' set.
87 : * Setting 'stopSignaled' is also used to handle the race condition when the
88 : * postmaster has not noticed the promotion yet and thus may end up restarting
89 : * the slot sync worker. If 'stopSignaled' is set, the worker will exit in such a
90 : * case. The SQL function pg_sync_replication_slots() will also error out if
91 : * this flag is set. Note that we don't need to reset this variable as after
92 : * promotion the slot sync worker won't be restarted because the pmState
93 : * changes to PM_RUN from PM_HOT_STANDBY and we don't support demoting
94 : * primary without restarting the server. See LaunchMissingBackgroundProcesses.
95 : *
96 : * The 'syncing' flag is needed to prevent concurrent slot syncs to avoid slot
97 : * overwrites.
98 : *
99 : * The 'last_start_time' is needed by postmaster to start the slot sync worker
100 : * once per SLOTSYNC_RESTART_INTERVAL_SEC. In cases where an immediate restart
101 : * is expected (e.g., slot sync GUCs change), slot sync worker will reset
102 : * last_start_time before exiting, so that postmaster can start the worker
103 : * without waiting for SLOTSYNC_RESTART_INTERVAL_SEC.
104 : */
105 : typedef struct SlotSyncCtxStruct
106 : {
107 : pid_t pid;
108 : bool stopSignaled;
109 : bool syncing;
110 : time_t last_start_time;
111 : slock_t mutex;
112 : } SlotSyncCtxStruct;
113 :
114 : static SlotSyncCtxStruct *SlotSyncCtx = NULL;
115 :
116 : /* GUC variable */
117 : bool sync_replication_slots = false;
118 :
119 : /*
120 : * The sleep time (ms) between slot-sync cycles varies dynamically
121 : * (within a MIN/MAX range) according to slot activity. See
122 : * wait_for_slot_activity() for details.
123 : */
124 : #define MIN_SLOTSYNC_WORKER_NAPTIME_MS 200
125 : #define MAX_SLOTSYNC_WORKER_NAPTIME_MS 30000 /* 30s */
126 :
127 : static long sleep_ms = MIN_SLOTSYNC_WORKER_NAPTIME_MS;
128 :
129 : /* The restart interval for slot sync work used by postmaster */
130 : #define SLOTSYNC_RESTART_INTERVAL_SEC 10
131 :
132 : /*
133 : * Flag to tell if we are syncing replication slots. Unlike the 'syncing' flag
134 : * in SlotSyncCtxStruct, this flag is true only if the current process is
135 : * performing slot synchronization.
136 : */
137 : static bool syncing_slots = false;
138 :
139 : /*
140 : * Structure to hold information fetched from the primary server about a logical
141 : * replication slot.
142 : */
143 : typedef struct RemoteSlot
144 : {
145 : char *name;
146 : char *plugin;
147 : char *database;
148 : bool two_phase;
149 : bool failover;
150 : XLogRecPtr restart_lsn;
151 : XLogRecPtr confirmed_lsn;
152 : XLogRecPtr two_phase_at;
153 : TransactionId catalog_xmin;
154 :
155 : /* RS_INVAL_NONE if valid, or the reason of invalidation */
156 : ReplicationSlotInvalidationCause invalidated;
157 : } RemoteSlot;
158 :
159 : static void slotsync_failure_callback(int code, Datum arg);
160 : static void update_synced_slots_inactive_since(void);
161 :
162 : /*
163 : * Update slot sync skip stats. This function requires the caller to acquire
164 : * the slot.
165 : */
166 : static void
167 78 : update_slotsync_skip_stats(SlotSyncSkipReason skip_reason)
168 : {
169 : ReplicationSlot *slot;
170 :
171 : Assert(MyReplicationSlot);
172 :
173 78 : slot = MyReplicationSlot;
174 :
175 : /*
176 : * Update the slot sync related stats in pg_stat_replication_slots when a
177 : * slot sync is skipped
178 : */
179 78 : if (skip_reason != SS_SKIP_NONE)
180 2 : pgstat_report_replslotsync(slot);
181 :
182 : /* Update the slot sync skip reason */
183 78 : if (slot->slotsync_skip_reason != skip_reason)
184 : {
185 4 : SpinLockAcquire(&slot->mutex);
186 4 : slot->slotsync_skip_reason = skip_reason;
187 4 : SpinLockRelease(&slot->mutex);
188 : }
189 78 : }
190 :
191 : /*
192 : * If necessary, update the local synced slot's metadata based on the data
193 : * from the remote slot.
194 : *
195 : * If no update was needed (the data of the remote slot is the same as the
196 : * local slot) return false, otherwise true.
197 : *
198 : * *found_consistent_snapshot will be true iff the remote slot's LSN or xmin is
199 : * modified, and decoding from the corresponding LSN's can reach a
200 : * consistent snapshot.
201 : *
202 : * *remote_slot_precedes will be true if the remote slot's LSN or xmin
203 : * precedes locally reserved position.
204 : */
205 : static bool
206 78 : update_local_synced_slot(RemoteSlot *remote_slot, Oid remote_dbid,
207 : bool *found_consistent_snapshot,
208 : bool *remote_slot_precedes)
209 : {
210 78 : ReplicationSlot *slot = MyReplicationSlot;
211 78 : bool updated_xmin_or_lsn = false;
212 78 : bool updated_config = false;
213 78 : SlotSyncSkipReason skip_reason = SS_SKIP_NONE;
214 :
215 : Assert(slot->data.invalidated == RS_INVAL_NONE);
216 :
217 78 : if (found_consistent_snapshot)
218 14 : *found_consistent_snapshot = false;
219 :
220 78 : if (remote_slot_precedes)
221 14 : *remote_slot_precedes = false;
222 :
223 : /*
224 : * Don't overwrite if we already have a newer catalog_xmin and
225 : * restart_lsn.
226 : */
227 156 : if (remote_slot->restart_lsn < slot->data.restart_lsn ||
228 78 : TransactionIdPrecedes(remote_slot->catalog_xmin,
229 : slot->data.catalog_xmin))
230 : {
231 : /* Update slot sync skip stats */
232 2 : update_slotsync_skip_stats(SS_SKIP_WAL_OR_ROWS_REMOVED);
233 :
234 : /*
235 : * This can happen in following situations:
236 : *
237 : * If the slot is temporary, it means either the initial WAL location
238 : * reserved for the local slot is ahead of the remote slot's
239 : * restart_lsn or the initial xmin_horizon computed for the local slot
240 : * is ahead of the remote slot.
241 : *
242 : * If the slot is persistent, both restart_lsn and catalog_xmin of the
243 : * synced slot could still be ahead of the remote slot. Since we use
244 : * slot advance functionality to keep snapbuild/slot updated, it is
245 : * possible that the restart_lsn and catalog_xmin are advanced to a
246 : * later position than it has on the primary. This can happen when
247 : * slot advancing machinery finds running xacts record after reaching
248 : * the consistent state at a later point than the primary where it
249 : * serializes the snapshot and updates the restart_lsn.
250 : *
251 : * We LOG the message if the slot is temporary as it can help the user
252 : * to understand why the slot is not sync-ready. In the case of a
253 : * persistent slot, it would be a more common case and won't directly
254 : * impact the users, so we used DEBUG1 level to log the message.
255 : */
256 2 : ereport(slot->data.persistency == RS_TEMPORARY ? LOG : DEBUG1,
257 : errmsg("could not synchronize replication slot \"%s\"",
258 : remote_slot->name),
259 : errdetail("Synchronization could lead to data loss, because the remote slot needs WAL at LSN %X/%08X and catalog xmin %u, but the standby has LSN %X/%08X and catalog xmin %u.",
260 : LSN_FORMAT_ARGS(remote_slot->restart_lsn),
261 : remote_slot->catalog_xmin,
262 : LSN_FORMAT_ARGS(slot->data.restart_lsn),
263 : slot->data.catalog_xmin));
264 :
265 2 : if (remote_slot_precedes)
266 2 : *remote_slot_precedes = true;
267 :
268 : /*
269 : * Skip updating the configuration. This is required to avoid syncing
270 : * two_phase_at without syncing confirmed_lsn. Otherwise, the prepared
271 : * transaction between old confirmed_lsn and two_phase_at will
272 : * unexpectedly get decoded and sent to the downstream after
273 : * promotion. See comments in ReorderBufferFinishPrepared.
274 : */
275 2 : return false;
276 : }
277 :
278 : /*
279 : * Attempt to sync LSNs and xmins only if remote slot is ahead of local
280 : * slot.
281 : */
282 76 : if (remote_slot->confirmed_lsn > slot->data.confirmed_flush ||
283 102 : remote_slot->restart_lsn > slot->data.restart_lsn ||
284 50 : TransactionIdFollows(remote_slot->catalog_xmin,
285 : slot->data.catalog_xmin))
286 : {
287 : /*
288 : * We can't directly copy the remote slot's LSN or xmin unless there
289 : * exists a consistent snapshot at that point. Otherwise, after
290 : * promotion, the slots may not reach a consistent point before the
291 : * confirmed_flush_lsn which can lead to a data loss. To avoid data
292 : * loss, we let slot machinery advance the slot which ensures that
293 : * snapbuilder/slot statuses are updated properly.
294 : */
295 26 : if (SnapBuildSnapshotExists(remote_slot->restart_lsn))
296 : {
297 : /*
298 : * Update the slot info directly if there is a serialized snapshot
299 : * at the restart_lsn, as the slot can quickly reach consistency
300 : * at restart_lsn by restoring the snapshot.
301 : */
302 6 : SpinLockAcquire(&slot->mutex);
303 6 : slot->data.restart_lsn = remote_slot->restart_lsn;
304 6 : slot->data.confirmed_flush = remote_slot->confirmed_lsn;
305 6 : slot->data.catalog_xmin = remote_slot->catalog_xmin;
306 6 : SpinLockRelease(&slot->mutex);
307 :
308 6 : if (found_consistent_snapshot)
309 0 : *found_consistent_snapshot = true;
310 : }
311 : else
312 : {
313 20 : LogicalSlotAdvanceAndCheckSnapState(remote_slot->confirmed_lsn,
314 : found_consistent_snapshot);
315 :
316 : /* Sanity check */
317 20 : if (slot->data.confirmed_flush != remote_slot->confirmed_lsn)
318 0 : ereport(ERROR,
319 : errmsg_internal("synchronized confirmed_flush for slot \"%s\" differs from remote slot",
320 : remote_slot->name),
321 : errdetail_internal("Remote slot has LSN %X/%08X but local slot has LSN %X/%08X.",
322 : LSN_FORMAT_ARGS(remote_slot->confirmed_lsn),
323 : LSN_FORMAT_ARGS(slot->data.confirmed_flush)));
324 :
325 : /*
326 : * If we can't reach a consistent snapshot, the slot won't be
327 : * persisted. See update_and_persist_local_synced_slot().
328 : */
329 20 : if (found_consistent_snapshot && !(*found_consistent_snapshot))
330 0 : skip_reason = SS_SKIP_NO_CONSISTENT_SNAPSHOT;
331 : }
332 :
333 26 : updated_xmin_or_lsn = true;
334 : }
335 :
336 : /* Update slot sync skip stats */
337 76 : update_slotsync_skip_stats(skip_reason);
338 :
339 76 : if (remote_dbid != slot->data.database ||
340 76 : remote_slot->two_phase != slot->data.two_phase ||
341 74 : remote_slot->failover != slot->data.failover ||
342 74 : strcmp(remote_slot->plugin, NameStr(slot->data.plugin)) != 0 ||
343 74 : remote_slot->two_phase_at != slot->data.two_phase_at)
344 : {
345 : NameData plugin_name;
346 :
347 : /* Avoid expensive operations while holding a spinlock. */
348 2 : namestrcpy(&plugin_name, remote_slot->plugin);
349 :
350 2 : SpinLockAcquire(&slot->mutex);
351 2 : slot->data.plugin = plugin_name;
352 2 : slot->data.database = remote_dbid;
353 2 : slot->data.two_phase = remote_slot->two_phase;
354 2 : slot->data.two_phase_at = remote_slot->two_phase_at;
355 2 : slot->data.failover = remote_slot->failover;
356 2 : SpinLockRelease(&slot->mutex);
357 :
358 2 : updated_config = true;
359 :
360 : /*
361 : * Ensure that there is no risk of sending prepared transactions
362 : * unexpectedly after the promotion.
363 : */
364 : Assert(slot->data.two_phase_at <= slot->data.confirmed_flush);
365 : }
366 :
367 : /*
368 : * We have to write the changed xmin to disk *before* we change the
369 : * in-memory value, otherwise after a crash we wouldn't know that some
370 : * catalog tuples might have been removed already.
371 : */
372 76 : if (updated_config || updated_xmin_or_lsn)
373 : {
374 28 : ReplicationSlotMarkDirty();
375 28 : ReplicationSlotSave();
376 : }
377 :
378 : /*
379 : * Now the new xmin is safely on disk, we can let the global value
380 : * advance. We do not take ProcArrayLock or similar since we only advance
381 : * xmin here and there's not much harm done by a concurrent computation
382 : * missing that.
383 : */
384 76 : if (updated_xmin_or_lsn)
385 : {
386 26 : SpinLockAcquire(&slot->mutex);
387 26 : slot->effective_catalog_xmin = remote_slot->catalog_xmin;
388 26 : SpinLockRelease(&slot->mutex);
389 :
390 26 : ReplicationSlotsComputeRequiredXmin(false);
391 26 : ReplicationSlotsComputeRequiredLSN();
392 : }
393 :
394 76 : return updated_config || updated_xmin_or_lsn;
395 : }
396 :
397 : /*
398 : * Get the list of local logical slots that are synchronized from the
399 : * primary server.
400 : */
401 : static List *
402 44 : get_local_synced_slots(void)
403 : {
404 44 : List *local_slots = NIL;
405 :
406 44 : LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
407 :
408 484 : for (int i = 0; i < max_replication_slots; i++)
409 : {
410 440 : ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
411 :
412 : /* Check if it is a synchronized slot */
413 440 : if (s->in_use && s->data.synced)
414 : {
415 : Assert(SlotIsLogical(s));
416 70 : local_slots = lappend(local_slots, s);
417 : }
418 : }
419 :
420 44 : LWLockRelease(ReplicationSlotControlLock);
421 :
422 44 : return local_slots;
423 : }
424 :
425 : /*
426 : * Helper function to check if local_slot is required to be retained.
427 : *
428 : * Return false either if local_slot does not exist in the remote_slots list
429 : * or is invalidated while the corresponding remote slot is still valid,
430 : * otherwise true.
431 : */
432 : static bool
433 70 : local_sync_slot_required(ReplicationSlot *local_slot, List *remote_slots)
434 : {
435 70 : bool remote_exists = false;
436 70 : bool locally_invalidated = false;
437 :
438 172 : foreach_ptr(RemoteSlot, remote_slot, remote_slots)
439 : {
440 100 : if (strcmp(remote_slot->name, NameStr(local_slot->data.name)) == 0)
441 : {
442 68 : remote_exists = true;
443 :
444 : /*
445 : * If remote slot is not invalidated but local slot is marked as
446 : * invalidated, then set locally_invalidated flag.
447 : */
448 68 : SpinLockAcquire(&local_slot->mutex);
449 68 : locally_invalidated =
450 136 : (remote_slot->invalidated == RS_INVAL_NONE) &&
451 68 : (local_slot->data.invalidated != RS_INVAL_NONE);
452 68 : SpinLockRelease(&local_slot->mutex);
453 :
454 68 : break;
455 : }
456 : }
457 :
458 70 : return (remote_exists && !locally_invalidated);
459 : }
460 :
461 : /*
462 : * Drop local obsolete slots.
463 : *
464 : * Drop the local slots that no longer need to be synced i.e. these either do
465 : * not exist on the primary or are no longer enabled for failover.
466 : *
467 : * Additionally, drop any slots that are valid on the primary but got
468 : * invalidated on the standby. This situation may occur due to the following
469 : * reasons:
470 : * - The 'max_slot_wal_keep_size' on the standby is insufficient to retain WAL
471 : * records from the restart_lsn of the slot.
472 : * - 'primary_slot_name' is temporarily reset to null and the physical slot is
473 : * removed.
474 : * These dropped slots will get recreated in next sync-cycle and it is okay to
475 : * drop and recreate such slots as long as these are not consumable on the
476 : * standby (which is the case currently).
477 : *
478 : * Note: Change of 'wal_level' on the primary server to a level lower than
479 : * logical may also result in slot invalidation and removal on the standby.
480 : * This is because such 'wal_level' change is only possible if the logical
481 : * slots are removed on the primary server, so it's expected to see the
482 : * slots being invalidated and removed on the standby too (and re-created
483 : * if they are re-created on the primary server).
484 : */
485 : static void
486 44 : drop_local_obsolete_slots(List *remote_slot_list)
487 : {
488 44 : List *local_slots = get_local_synced_slots();
489 :
490 158 : foreach_ptr(ReplicationSlot, local_slot, local_slots)
491 : {
492 : /* Drop the local slot if it is not required to be retained. */
493 70 : if (!local_sync_slot_required(local_slot, remote_slot_list))
494 : {
495 : bool synced_slot;
496 :
497 : /*
498 : * Use shared lock to prevent a conflict with
499 : * ReplicationSlotsDropDBSlots(), trying to drop the same slot
500 : * during a drop-database operation.
501 : */
502 4 : LockSharedObject(DatabaseRelationId, local_slot->data.database,
503 : 0, AccessShareLock);
504 :
505 : /*
506 : * In the small window between getting the slot to drop and
507 : * locking the database, there is a possibility of a parallel
508 : * database drop by the startup process and the creation of a new
509 : * slot by the user. This new user-created slot may end up using
510 : * the same shared memory as that of 'local_slot'. Thus check if
511 : * local_slot is still the synced one before performing actual
512 : * drop.
513 : */
514 4 : SpinLockAcquire(&local_slot->mutex);
515 4 : synced_slot = local_slot->in_use && local_slot->data.synced;
516 4 : SpinLockRelease(&local_slot->mutex);
517 :
518 4 : if (synced_slot)
519 : {
520 4 : ReplicationSlotAcquire(NameStr(local_slot->data.name), true, false);
521 4 : ReplicationSlotDropAcquired();
522 : }
523 :
524 4 : UnlockSharedObject(DatabaseRelationId, local_slot->data.database,
525 : 0, AccessShareLock);
526 :
527 4 : ereport(LOG,
528 : errmsg("dropped replication slot \"%s\" of database with OID %u",
529 : NameStr(local_slot->data.name),
530 : local_slot->data.database));
531 : }
532 : }
533 44 : }
534 :
535 : /*
536 : * Reserve WAL for the currently active local slot using the specified WAL
537 : * location (restart_lsn).
538 : *
539 : * If the given WAL location has been removed, reserve WAL using the oldest
540 : * existing WAL segment.
541 : */
542 : static void
543 12 : reserve_wal_for_local_slot(XLogRecPtr restart_lsn)
544 : {
545 : XLogSegNo oldest_segno;
546 : XLogSegNo segno;
547 12 : ReplicationSlot *slot = MyReplicationSlot;
548 :
549 : Assert(slot != NULL);
550 : Assert(!XLogRecPtrIsValid(slot->data.restart_lsn));
551 :
552 : while (true)
553 : {
554 12 : SpinLockAcquire(&slot->mutex);
555 12 : slot->data.restart_lsn = restart_lsn;
556 12 : SpinLockRelease(&slot->mutex);
557 :
558 : /* Prevent WAL removal as fast as possible */
559 12 : ReplicationSlotsComputeRequiredLSN();
560 :
561 12 : XLByteToSeg(slot->data.restart_lsn, segno, wal_segment_size);
562 :
563 : /*
564 : * Find the oldest existing WAL segment file.
565 : *
566 : * Normally, we can determine it by using the last removed segment
567 : * number. However, if no WAL segment files have been removed by a
568 : * checkpoint since startup, we need to search for the oldest segment
569 : * file from the current timeline existing in XLOGDIR.
570 : *
571 : * XXX: Currently, we are searching for the oldest segment in the
572 : * current timeline as there is less chance of the slot's restart_lsn
573 : * from being some prior timeline, and even if it happens, in the
574 : * worst case, we will wait to sync till the slot's restart_lsn moved
575 : * to the current timeline.
576 : */
577 12 : oldest_segno = XLogGetLastRemovedSegno() + 1;
578 :
579 12 : if (oldest_segno == 1)
580 : {
581 : TimeLineID cur_timeline;
582 :
583 8 : GetWalRcvFlushRecPtr(NULL, &cur_timeline);
584 8 : oldest_segno = XLogGetOldestSegno(cur_timeline);
585 : }
586 :
587 12 : elog(DEBUG1, "segno: " UINT64_FORMAT " of purposed restart_lsn for the synced slot, oldest_segno: " UINT64_FORMAT " available",
588 : segno, oldest_segno);
589 :
590 : /*
591 : * If all required WAL is still there, great, otherwise retry. The
592 : * slot should prevent further removal of WAL, unless there's a
593 : * concurrent ReplicationSlotsComputeRequiredLSN() after we've written
594 : * the new restart_lsn above, so normally we should never need to loop
595 : * more than twice.
596 : */
597 12 : if (segno >= oldest_segno)
598 12 : break;
599 :
600 : /* Retry using the location of the oldest wal segment */
601 0 : XLogSegNoOffsetToRecPtr(oldest_segno, 0, wal_segment_size, restart_lsn);
602 : }
603 12 : }
604 :
605 : /*
606 : * If the remote restart_lsn and catalog_xmin have caught up with the
607 : * local ones, then update the LSNs and persist the local synced slot for
608 : * future synchronization; otherwise, do nothing.
609 : *
610 : * *slot_persistence_pending is set to true if any of the slots fail to
611 : * persist.
612 : *
613 : * Return true if the slot is marked as RS_PERSISTENT (sync-ready), otherwise
614 : * false.
615 : */
616 : static bool
617 14 : update_and_persist_local_synced_slot(RemoteSlot *remote_slot, Oid remote_dbid,
618 : bool *slot_persistence_pending)
619 : {
620 14 : ReplicationSlot *slot = MyReplicationSlot;
621 14 : bool found_consistent_snapshot = false;
622 14 : bool remote_slot_precedes = false;
623 :
624 : /* Slotsync skip stats are handled in function update_local_synced_slot() */
625 14 : (void) update_local_synced_slot(remote_slot, remote_dbid,
626 : &found_consistent_snapshot,
627 : &remote_slot_precedes);
628 :
629 : /*
630 : * Check if the primary server has caught up. Refer to the comment atop
631 : * the file for details on this check.
632 : */
633 14 : if (remote_slot_precedes)
634 : {
635 : /*
636 : * The remote slot didn't catch up to locally reserved position.
637 : *
638 : * We do not drop the slot because the restart_lsn can be ahead of the
639 : * current location when recreating the slot in the next cycle. It may
640 : * take more time to create such a slot. Therefore, we keep this slot
641 : * and attempt the synchronization in the next cycle.
642 : *
643 : * We also update the slot_persistence_pending parameter, so the SQL
644 : * function can retry.
645 : */
646 2 : if (slot_persistence_pending)
647 2 : *slot_persistence_pending = true;
648 :
649 2 : return false;
650 : }
651 :
652 : /*
653 : * Don't persist the slot if it cannot reach the consistent point from the
654 : * restart_lsn. See comments atop this file.
655 : */
656 12 : if (!found_consistent_snapshot)
657 : {
658 0 : ereport(LOG,
659 : errmsg("could not synchronize replication slot \"%s\"", remote_slot->name),
660 : errdetail("Synchronization could lead to data loss, because the standby could not build a consistent snapshot to decode WALs at LSN %X/%08X.",
661 : LSN_FORMAT_ARGS(slot->data.restart_lsn)));
662 :
663 : /* Set this, so that SQL function can retry */
664 0 : if (slot_persistence_pending)
665 0 : *slot_persistence_pending = true;
666 :
667 0 : return false;
668 : }
669 :
670 12 : ReplicationSlotPersist();
671 :
672 12 : ereport(LOG,
673 : errmsg("newly created replication slot \"%s\" is sync-ready now",
674 : remote_slot->name));
675 :
676 12 : return true;
677 : }
678 :
679 : /*
680 : * Synchronize a single slot to the given position.
681 : *
682 : * This creates a new slot if there is no existing one and updates the
683 : * metadata of the slot as per the data received from the primary server.
684 : *
685 : * The slot is created as a temporary slot and stays in the same state until the
686 : * remote_slot catches up with locally reserved position and local slot is
687 : * updated. The slot is then persisted and is considered as sync-ready for
688 : * periodic syncs.
689 : *
690 : * *slot_persistence_pending is set to true if any of the slots fail to
691 : * persist.
692 : *
693 : * Returns TRUE if the local slot is updated.
694 : */
695 : static bool
696 78 : synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
697 : bool *slot_persistence_pending)
698 : {
699 : ReplicationSlot *slot;
700 78 : XLogRecPtr latestFlushPtr = GetStandbyFlushRecPtr(NULL);
701 78 : bool slot_updated = false;
702 :
703 : /* Search for the named slot */
704 78 : if ((slot = SearchNamedReplicationSlot(remote_slot->name, true)))
705 : {
706 : bool synced;
707 :
708 66 : SpinLockAcquire(&slot->mutex);
709 66 : synced = slot->data.synced;
710 66 : SpinLockRelease(&slot->mutex);
711 :
712 : /* User-created slot with the same name exists, raise ERROR. */
713 66 : if (!synced)
714 0 : ereport(ERROR,
715 : errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
716 : errmsg("exiting from slot synchronization because same"
717 : " name slot \"%s\" already exists on the standby",
718 : remote_slot->name));
719 :
720 : /*
721 : * The slot has been synchronized before.
722 : *
723 : * It is important to acquire the slot here before checking
724 : * invalidation. If we don't acquire the slot first, there could be a
725 : * race condition that the local slot could be invalidated just after
726 : * checking the 'invalidated' flag here and we could end up
727 : * overwriting 'invalidated' flag to remote_slot's value. See
728 : * InvalidatePossiblyObsoleteSlot() where it invalidates slot directly
729 : * if the slot is not acquired by other processes.
730 : *
731 : * XXX: If it ever turns out that slot acquire/release is costly for
732 : * cases when none of the slot properties is changed then we can do a
733 : * pre-check to ensure that at least one of the slot properties is
734 : * changed before acquiring the slot.
735 : */
736 66 : ReplicationSlotAcquire(remote_slot->name, true, false);
737 :
738 : Assert(slot == MyReplicationSlot);
739 :
740 : /*
741 : * Copy the invalidation cause from remote only if local slot is not
742 : * invalidated locally, we don't want to overwrite existing one.
743 : */
744 66 : if (slot->data.invalidated == RS_INVAL_NONE &&
745 66 : remote_slot->invalidated != RS_INVAL_NONE)
746 : {
747 0 : SpinLockAcquire(&slot->mutex);
748 0 : slot->data.invalidated = remote_slot->invalidated;
749 0 : SpinLockRelease(&slot->mutex);
750 :
751 : /* Make sure the invalidated state persists across server restart */
752 0 : ReplicationSlotMarkDirty();
753 0 : ReplicationSlotSave();
754 :
755 0 : slot_updated = true;
756 : }
757 :
758 : /* Skip the sync of an invalidated slot */
759 66 : if (slot->data.invalidated != RS_INVAL_NONE)
760 : {
761 0 : update_slotsync_skip_stats(SS_SKIP_INVALID);
762 :
763 0 : ReplicationSlotRelease();
764 0 : return slot_updated;
765 : }
766 :
767 : /*
768 : * Make sure that concerned WAL is received and flushed before syncing
769 : * slot to target lsn received from the primary server.
770 : *
771 : * Report statistics only after the slot has been acquired, ensuring
772 : * it cannot be dropped during the reporting process.
773 : */
774 66 : if (remote_slot->confirmed_lsn > latestFlushPtr)
775 : {
776 0 : update_slotsync_skip_stats(SS_SKIP_WAL_NOT_FLUSHED);
777 :
778 : /*
779 : * Can get here only if GUC 'synchronized_standby_slots' on the
780 : * primary server was not configured correctly.
781 : */
782 0 : ereport(AmLogicalSlotSyncWorkerProcess() ? LOG : ERROR,
783 : errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
784 : errmsg("skipping slot synchronization because the received slot sync"
785 : " LSN %X/%08X for slot \"%s\" is ahead of the standby position %X/%08X",
786 : LSN_FORMAT_ARGS(remote_slot->confirmed_lsn),
787 : remote_slot->name,
788 : LSN_FORMAT_ARGS(latestFlushPtr)));
789 :
790 0 : ReplicationSlotRelease();
791 :
792 0 : return slot_updated;
793 : }
794 :
795 : /* Slot not ready yet, let's attempt to make it sync-ready now. */
796 66 : if (slot->data.persistency == RS_TEMPORARY)
797 : {
798 2 : slot_updated = update_and_persist_local_synced_slot(remote_slot,
799 : remote_dbid,
800 : slot_persistence_pending);
801 : }
802 :
803 : /* Slot ready for sync, so sync it. */
804 : else
805 : {
806 : /*
807 : * Sanity check: As long as the invalidations are handled
808 : * appropriately as above, this should never happen.
809 : *
810 : * We don't need to check restart_lsn here. See the comments in
811 : * update_local_synced_slot() for details.
812 : */
813 64 : if (remote_slot->confirmed_lsn < slot->data.confirmed_flush)
814 0 : ereport(ERROR,
815 : errmsg_internal("cannot synchronize local slot \"%s\"",
816 : remote_slot->name),
817 : errdetail_internal("Local slot's start streaming location LSN(%X/%08X) is ahead of remote slot's LSN(%X/%08X).",
818 : LSN_FORMAT_ARGS(slot->data.confirmed_flush),
819 : LSN_FORMAT_ARGS(remote_slot->confirmed_lsn)));
820 :
821 64 : slot_updated = update_local_synced_slot(remote_slot, remote_dbid,
822 : NULL, NULL);
823 : }
824 : }
825 : /* Otherwise create the slot first. */
826 : else
827 : {
828 : NameData plugin_name;
829 12 : TransactionId xmin_horizon = InvalidTransactionId;
830 :
831 : /* Skip creating the local slot if remote_slot is invalidated already */
832 12 : if (remote_slot->invalidated != RS_INVAL_NONE)
833 0 : return false;
834 :
835 : /*
836 : * We create temporary slots instead of ephemeral slots here because
837 : * we want the slots to survive after releasing them. This is done to
838 : * avoid dropping and re-creating the slots in each synchronization
839 : * cycle if the restart_lsn or catalog_xmin of the remote slot has not
840 : * caught up.
841 : */
842 12 : ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
843 12 : remote_slot->two_phase,
844 12 : remote_slot->failover,
845 : true);
846 :
847 : /* For shorter lines. */
848 12 : slot = MyReplicationSlot;
849 :
850 : /* Avoid expensive operations while holding a spinlock. */
851 12 : namestrcpy(&plugin_name, remote_slot->plugin);
852 :
853 12 : SpinLockAcquire(&slot->mutex);
854 12 : slot->data.database = remote_dbid;
855 12 : slot->data.plugin = plugin_name;
856 12 : SpinLockRelease(&slot->mutex);
857 :
858 12 : reserve_wal_for_local_slot(remote_slot->restart_lsn);
859 :
860 12 : LWLockAcquire(ReplicationSlotControlLock, LW_EXCLUSIVE);
861 12 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
862 12 : xmin_horizon = GetOldestSafeDecodingTransactionId(true);
863 12 : SpinLockAcquire(&slot->mutex);
864 12 : slot->effective_catalog_xmin = xmin_horizon;
865 12 : slot->data.catalog_xmin = xmin_horizon;
866 12 : SpinLockRelease(&slot->mutex);
867 12 : ReplicationSlotsComputeRequiredXmin(true);
868 12 : LWLockRelease(ProcArrayLock);
869 12 : LWLockRelease(ReplicationSlotControlLock);
870 :
871 : /*
872 : * Make sure that concerned WAL is received and flushed before syncing
873 : * slot to target lsn received from the primary server.
874 : *
875 : * Report statistics only after the slot has been acquired, ensuring
876 : * it cannot be dropped during the reporting process.
877 : */
878 12 : if (remote_slot->confirmed_lsn > latestFlushPtr)
879 : {
880 0 : update_slotsync_skip_stats(SS_SKIP_WAL_NOT_FLUSHED);
881 :
882 : /*
883 : * Can get here only if GUC 'synchronized_standby_slots' on the
884 : * primary server was not configured correctly.
885 : */
886 0 : ereport(AmLogicalSlotSyncWorkerProcess() ? LOG : ERROR,
887 : errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
888 : errmsg("skipping slot synchronization because the received slot sync"
889 : " LSN %X/%08X for slot \"%s\" is ahead of the standby position %X/%08X",
890 : LSN_FORMAT_ARGS(remote_slot->confirmed_lsn),
891 : remote_slot->name,
892 : LSN_FORMAT_ARGS(latestFlushPtr)));
893 :
894 0 : ReplicationSlotRelease();
895 :
896 0 : return false;
897 : }
898 :
899 12 : update_and_persist_local_synced_slot(remote_slot, remote_dbid,
900 : slot_persistence_pending);
901 :
902 12 : slot_updated = true;
903 : }
904 :
905 78 : ReplicationSlotRelease();
906 :
907 78 : return slot_updated;
908 : }
909 :
910 : /*
911 : * Fetch remote slots.
912 : *
913 : * If slot_names is NIL, fetches all failover logical slots from the
914 : * primary server, otherwise fetches only the ones with names in slot_names.
915 : *
916 : * Returns a list of remote slot information structures, or NIL if none
917 : * are found.
918 : */
919 : static List *
920 44 : fetch_remote_slots(WalReceiverConn *wrconn, List *slot_names)
921 : {
922 : #define SLOTSYNC_COLUMN_COUNT 10
923 44 : Oid slotRow[SLOTSYNC_COLUMN_COUNT] = {TEXTOID, TEXTOID, LSNOID,
924 : LSNOID, XIDOID, BOOLOID, LSNOID, BOOLOID, TEXTOID, TEXTOID};
925 :
926 : WalRcvExecResult *res;
927 : TupleTableSlot *tupslot;
928 44 : List *remote_slot_list = NIL;
929 : StringInfoData query;
930 :
931 44 : initStringInfo(&query);
932 44 : appendStringInfoString(&query,
933 : "SELECT slot_name, plugin, confirmed_flush_lsn,"
934 : " restart_lsn, catalog_xmin, two_phase,"
935 : " two_phase_at, failover,"
936 : " database, invalidation_reason"
937 : " FROM pg_catalog.pg_replication_slots"
938 : " WHERE failover and NOT temporary");
939 :
940 44 : if (slot_names != NIL)
941 : {
942 2 : bool first_slot = true;
943 :
944 : /*
945 : * Construct the query to fetch only the specified slots
946 : */
947 2 : appendStringInfoString(&query, " AND slot_name IN (");
948 :
949 6 : foreach_ptr(char, slot_name, slot_names)
950 : {
951 2 : if (!first_slot)
952 0 : appendStringInfoString(&query, ", ");
953 :
954 2 : appendStringInfo(&query, "%s", quote_literal_cstr(slot_name));
955 2 : first_slot = false;
956 : }
957 2 : appendStringInfoChar(&query, ')');
958 : }
959 :
960 : /* Execute the query */
961 44 : res = walrcv_exec(wrconn, query.data, SLOTSYNC_COLUMN_COUNT, slotRow);
962 44 : pfree(query.data);
963 44 : if (res->status != WALRCV_OK_TUPLES)
964 0 : ereport(ERROR,
965 : errmsg("could not fetch failover logical slots info from the primary server: %s",
966 : res->err));
967 :
968 44 : tupslot = MakeSingleTupleTableSlot(res->tupledesc, &TTSOpsMinimalTuple);
969 122 : while (tuplestore_gettupleslot(res->tuplestore, true, false, tupslot))
970 : {
971 : bool isnull;
972 78 : RemoteSlot *remote_slot = palloc0_object(RemoteSlot);
973 : Datum d;
974 78 : int col = 0;
975 :
976 78 : remote_slot->name = TextDatumGetCString(slot_getattr(tupslot, ++col,
977 : &isnull));
978 : Assert(!isnull);
979 :
980 78 : remote_slot->plugin = TextDatumGetCString(slot_getattr(tupslot, ++col,
981 : &isnull));
982 : Assert(!isnull);
983 :
984 : /*
985 : * It is possible to get null values for LSN and Xmin if slot is
986 : * invalidated on the primary server, so handle accordingly.
987 : */
988 78 : d = slot_getattr(tupslot, ++col, &isnull);
989 78 : remote_slot->confirmed_lsn = isnull ? InvalidXLogRecPtr :
990 78 : DatumGetLSN(d);
991 :
992 78 : d = slot_getattr(tupslot, ++col, &isnull);
993 78 : remote_slot->restart_lsn = isnull ? InvalidXLogRecPtr : DatumGetLSN(d);
994 :
995 78 : d = slot_getattr(tupslot, ++col, &isnull);
996 78 : remote_slot->catalog_xmin = isnull ? InvalidTransactionId :
997 78 : DatumGetTransactionId(d);
998 :
999 78 : remote_slot->two_phase = DatumGetBool(slot_getattr(tupslot, ++col,
1000 : &isnull));
1001 : Assert(!isnull);
1002 :
1003 78 : d = slot_getattr(tupslot, ++col, &isnull);
1004 78 : remote_slot->two_phase_at = isnull ? InvalidXLogRecPtr : DatumGetLSN(d);
1005 :
1006 78 : remote_slot->failover = DatumGetBool(slot_getattr(tupslot, ++col,
1007 : &isnull));
1008 : Assert(!isnull);
1009 :
1010 78 : remote_slot->database = TextDatumGetCString(slot_getattr(tupslot,
1011 : ++col, &isnull));
1012 : Assert(!isnull);
1013 :
1014 78 : d = slot_getattr(tupslot, ++col, &isnull);
1015 78 : remote_slot->invalidated = isnull ? RS_INVAL_NONE :
1016 0 : GetSlotInvalidationCause(TextDatumGetCString(d));
1017 :
1018 : /* Sanity check */
1019 : Assert(col == SLOTSYNC_COLUMN_COUNT);
1020 :
1021 : /*
1022 : * If restart_lsn, confirmed_lsn or catalog_xmin is invalid but the
1023 : * slot is valid, that means we have fetched the remote_slot in its
1024 : * RS_EPHEMERAL state. In such a case, don't sync it; we can always
1025 : * sync it in the next sync cycle when the remote_slot is persisted
1026 : * and has valid lsn(s) and xmin values.
1027 : *
1028 : * XXX: In future, if we plan to expose 'slot->data.persistency' in
1029 : * pg_replication_slots view, then we can avoid fetching RS_EPHEMERAL
1030 : * slots in the first place.
1031 : */
1032 78 : if ((!XLogRecPtrIsValid(remote_slot->restart_lsn) ||
1033 78 : !XLogRecPtrIsValid(remote_slot->confirmed_lsn) ||
1034 78 : !TransactionIdIsValid(remote_slot->catalog_xmin)) &&
1035 0 : remote_slot->invalidated == RS_INVAL_NONE)
1036 0 : pfree(remote_slot);
1037 : else
1038 : /* Create list of remote slots */
1039 78 : remote_slot_list = lappend(remote_slot_list, remote_slot);
1040 :
1041 78 : ExecClearTuple(tupslot);
1042 : }
1043 :
1044 44 : walrcv_clear_result(res);
1045 :
1046 44 : return remote_slot_list;
1047 : }
1048 :
1049 : /*
1050 : * Synchronize slots.
1051 : *
1052 : * This function takes a list of remote slots and synchronizes them locally. It
1053 : * creates the slots if not present on the standby and updates existing ones.
1054 : *
1055 : * If slot_persistence_pending is not NULL, it will be set to true if one or
1056 : * more slots could not be persisted. This allows callers such as
1057 : * SyncReplicationSlots() to retry those slots.
1058 : *
1059 : * Returns TRUE if any of the slots gets updated in this sync-cycle.
1060 : */
1061 : static bool
1062 44 : synchronize_slots(WalReceiverConn *wrconn, List *remote_slot_list,
1063 : bool *slot_persistence_pending)
1064 : {
1065 44 : bool some_slot_updated = false;
1066 :
1067 : /* Drop local slots that no longer need to be synced. */
1068 44 : drop_local_obsolete_slots(remote_slot_list);
1069 :
1070 : /* Now sync the slots locally */
1071 166 : foreach_ptr(RemoteSlot, remote_slot, remote_slot_list)
1072 : {
1073 78 : Oid remote_dbid = get_database_oid(remote_slot->database, false);
1074 :
1075 : /*
1076 : * Use shared lock to prevent a conflict with
1077 : * ReplicationSlotsDropDBSlots(), trying to drop the same slot during
1078 : * a drop-database operation.
1079 : */
1080 78 : LockSharedObject(DatabaseRelationId, remote_dbid, 0, AccessShareLock);
1081 :
1082 78 : some_slot_updated |= synchronize_one_slot(remote_slot, remote_dbid,
1083 : slot_persistence_pending);
1084 :
1085 78 : UnlockSharedObject(DatabaseRelationId, remote_dbid, 0, AccessShareLock);
1086 : }
1087 :
1088 44 : return some_slot_updated;
1089 : }
1090 :
1091 : /*
1092 : * Checks the remote server info.
1093 : *
1094 : * We ensure that the 'primary_slot_name' exists on the remote server and the
1095 : * remote server is not a standby node.
1096 : */
1097 : static void
1098 26 : validate_remote_info(WalReceiverConn *wrconn)
1099 : {
1100 : #define PRIMARY_INFO_OUTPUT_COL_COUNT 2
1101 : WalRcvExecResult *res;
1102 26 : Oid slotRow[PRIMARY_INFO_OUTPUT_COL_COUNT] = {BOOLOID, BOOLOID};
1103 : StringInfoData cmd;
1104 : bool isnull;
1105 : TupleTableSlot *tupslot;
1106 : bool remote_in_recovery;
1107 : bool primary_slot_valid;
1108 26 : bool started_tx = false;
1109 :
1110 26 : initStringInfo(&cmd);
1111 26 : appendStringInfo(&cmd,
1112 : "SELECT pg_is_in_recovery(), count(*) = 1"
1113 : " FROM pg_catalog.pg_replication_slots"
1114 : " WHERE slot_type='physical' AND slot_name=%s",
1115 : quote_literal_cstr(PrimarySlotName));
1116 :
1117 : /* The syscache access in walrcv_exec() needs a transaction env. */
1118 26 : if (!IsTransactionState())
1119 : {
1120 8 : StartTransactionCommand();
1121 8 : started_tx = true;
1122 : }
1123 :
1124 26 : res = walrcv_exec(wrconn, cmd.data, PRIMARY_INFO_OUTPUT_COL_COUNT, slotRow);
1125 26 : pfree(cmd.data);
1126 :
1127 26 : if (res->status != WALRCV_OK_TUPLES)
1128 0 : ereport(ERROR,
1129 : errmsg("could not fetch primary slot name \"%s\" info from the primary server: %s",
1130 : PrimarySlotName, res->err),
1131 : errhint("Check if \"primary_slot_name\" is configured correctly."));
1132 :
1133 26 : tupslot = MakeSingleTupleTableSlot(res->tupledesc, &TTSOpsMinimalTuple);
1134 26 : if (!tuplestore_gettupleslot(res->tuplestore, true, false, tupslot))
1135 0 : elog(ERROR,
1136 : "failed to fetch tuple for the primary server slot specified by \"primary_slot_name\"");
1137 :
1138 26 : remote_in_recovery = DatumGetBool(slot_getattr(tupslot, 1, &isnull));
1139 : Assert(!isnull);
1140 :
1141 : /*
1142 : * Slot sync is currently not supported on a cascading standby. This is
1143 : * because if we allow it, the primary server needs to wait for all the
1144 : * cascading standbys, otherwise, logical subscribers can still be ahead
1145 : * of one of the cascading standbys which we plan to promote. Thus, to
1146 : * avoid this additional complexity, we restrict it for the time being.
1147 : */
1148 26 : if (remote_in_recovery)
1149 2 : ereport(ERROR,
1150 : errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
1151 : errmsg("cannot synchronize replication slots from a standby server"));
1152 :
1153 24 : primary_slot_valid = DatumGetBool(slot_getattr(tupslot, 2, &isnull));
1154 : Assert(!isnull);
1155 :
1156 24 : if (!primary_slot_valid)
1157 0 : ereport(ERROR,
1158 : errcode(ERRCODE_INVALID_PARAMETER_VALUE),
1159 : /* translator: second %s is a GUC variable name */
1160 : errmsg("replication slot \"%s\" specified by \"%s\" does not exist on primary server",
1161 : PrimarySlotName, "primary_slot_name"));
1162 :
1163 24 : ExecClearTuple(tupslot);
1164 24 : walrcv_clear_result(res);
1165 :
1166 24 : if (started_tx)
1167 8 : CommitTransactionCommand();
1168 24 : }
1169 :
1170 : /*
1171 : * Checks if dbname is specified in 'primary_conninfo'.
1172 : *
1173 : * Error out if not specified otherwise return it.
1174 : */
1175 : char *
1176 28 : CheckAndGetDbnameFromConninfo(void)
1177 : {
1178 : char *dbname;
1179 :
1180 : /*
1181 : * The slot synchronization needs a database connection for walrcv_exec to
1182 : * work.
1183 : */
1184 28 : dbname = walrcv_get_dbname_from_conninfo(PrimaryConnInfo);
1185 28 : if (dbname == NULL)
1186 2 : ereport(ERROR,
1187 : errcode(ERRCODE_INVALID_PARAMETER_VALUE),
1188 :
1189 : /*
1190 : * translator: first %s is a connection option; second %s is a GUC
1191 : * variable name
1192 : */
1193 : errmsg("replication slot synchronization requires \"%s\" to be specified in \"%s\"",
1194 : "dbname", "primary_conninfo"));
1195 26 : return dbname;
1196 : }
1197 :
1198 : /*
1199 : * Return true if all necessary GUCs for slot synchronization are set
1200 : * appropriately, otherwise, return false.
1201 : */
1202 : bool
1203 34 : ValidateSlotSyncParams(int elevel)
1204 : {
1205 : /*
1206 : * Logical slot sync/creation requires logical decoding to be enabled.
1207 : */
1208 34 : if (!IsLogicalDecodingEnabled())
1209 : {
1210 0 : ereport(elevel,
1211 : errcode(ERRCODE_INVALID_PARAMETER_VALUE),
1212 : errmsg("replication slot synchronization requires \"effective_wal_level\" >= \"logical\" on the primary"),
1213 : errhint("To enable logical decoding on primary, set \"wal_level\" >= \"logical\" or create at least one logical slot when \"wal_level\" = \"replica\"."));
1214 :
1215 0 : return false;
1216 : }
1217 :
1218 : /*
1219 : * A physical replication slot(primary_slot_name) is required on the
1220 : * primary to ensure that the rows needed by the standby are not removed
1221 : * after restarting, so that the synchronized slot on the standby will not
1222 : * be invalidated.
1223 : */
1224 34 : if (PrimarySlotName == NULL || *PrimarySlotName == '\0')
1225 : {
1226 0 : ereport(elevel,
1227 : errcode(ERRCODE_INVALID_PARAMETER_VALUE),
1228 : /* translator: %s is a GUC variable name */
1229 : errmsg("replication slot synchronization requires \"%s\" to be set", "primary_slot_name"));
1230 0 : return false;
1231 : }
1232 :
1233 : /*
1234 : * hot_standby_feedback must be enabled to cooperate with the physical
1235 : * replication slot, which allows informing the primary about the xmin and
1236 : * catalog_xmin values on the standby.
1237 : */
1238 34 : if (!hot_standby_feedback)
1239 : {
1240 2 : ereport(elevel,
1241 : errcode(ERRCODE_INVALID_PARAMETER_VALUE),
1242 : /* translator: %s is a GUC variable name */
1243 : errmsg("replication slot synchronization requires \"%s\" to be enabled",
1244 : "hot_standby_feedback"));
1245 2 : return false;
1246 : }
1247 :
1248 : /*
1249 : * The primary_conninfo is required to make connection to primary for
1250 : * getting slots information.
1251 : */
1252 32 : if (PrimaryConnInfo == NULL || *PrimaryConnInfo == '\0')
1253 : {
1254 0 : ereport(elevel,
1255 : errcode(ERRCODE_INVALID_PARAMETER_VALUE),
1256 : /* translator: %s is a GUC variable name */
1257 : errmsg("replication slot synchronization requires \"%s\" to be set",
1258 : "primary_conninfo"));
1259 0 : return false;
1260 : }
1261 :
1262 32 : return true;
1263 : }
1264 :
1265 : /*
1266 : * Re-read the config file for slot synchronization.
1267 : *
1268 : * Exit or throw error if relevant GUCs have changed depending on whether
1269 : * called from slot sync worker or from the SQL function pg_sync_replication_slots()
1270 : */
1271 : static void
1272 2 : slotsync_reread_config(void)
1273 : {
1274 2 : char *old_primary_conninfo = pstrdup(PrimaryConnInfo);
1275 2 : char *old_primary_slotname = pstrdup(PrimarySlotName);
1276 2 : bool old_sync_replication_slots = sync_replication_slots;
1277 2 : bool old_hot_standby_feedback = hot_standby_feedback;
1278 : bool conninfo_changed;
1279 : bool primary_slotname_changed;
1280 2 : bool is_slotsync_worker = AmLogicalSlotSyncWorkerProcess();
1281 2 : bool parameter_changed = false;
1282 :
1283 : if (is_slotsync_worker)
1284 : Assert(sync_replication_slots);
1285 :
1286 2 : ConfigReloadPending = false;
1287 2 : ProcessConfigFile(PGC_SIGHUP);
1288 :
1289 2 : conninfo_changed = strcmp(old_primary_conninfo, PrimaryConnInfo) != 0;
1290 2 : primary_slotname_changed = strcmp(old_primary_slotname, PrimarySlotName) != 0;
1291 2 : pfree(old_primary_conninfo);
1292 2 : pfree(old_primary_slotname);
1293 :
1294 2 : if (old_sync_replication_slots != sync_replication_slots)
1295 : {
1296 0 : if (is_slotsync_worker)
1297 : {
1298 0 : ereport(LOG,
1299 : /* translator: %s is a GUC variable name */
1300 : errmsg("replication slot synchronization worker will stop because \"%s\" is disabled",
1301 : "sync_replication_slots"));
1302 :
1303 0 : proc_exit(0);
1304 : }
1305 :
1306 0 : parameter_changed = true;
1307 : }
1308 : else
1309 : {
1310 2 : if (conninfo_changed ||
1311 2 : primary_slotname_changed ||
1312 2 : (old_hot_standby_feedback != hot_standby_feedback))
1313 : {
1314 :
1315 2 : if (is_slotsync_worker)
1316 : {
1317 2 : ereport(LOG,
1318 : errmsg("replication slot synchronization worker will restart because of a parameter change"));
1319 :
1320 : /*
1321 : * Reset the last-start time for this worker so that the
1322 : * postmaster can restart it without waiting for
1323 : * SLOTSYNC_RESTART_INTERVAL_SEC.
1324 : */
1325 2 : SlotSyncCtx->last_start_time = 0;
1326 :
1327 2 : proc_exit(0);
1328 : }
1329 :
1330 0 : parameter_changed = true;
1331 : }
1332 : }
1333 :
1334 : /*
1335 : * If we have reached here with a parameter change, we must be running in
1336 : * SQL function, emit error in such a case.
1337 : */
1338 0 : if (parameter_changed)
1339 : {
1340 : Assert(!is_slotsync_worker);
1341 0 : ereport(ERROR,
1342 : errcode(ERRCODE_INVALID_PARAMETER_VALUE),
1343 : errmsg("replication slot synchronization will stop because of a parameter change"));
1344 : }
1345 :
1346 0 : }
1347 :
1348 : /*
1349 : * Interrupt handler for process performing slot synchronization.
1350 : */
1351 : static void
1352 70 : ProcessSlotSyncInterrupts(void)
1353 : {
1354 70 : CHECK_FOR_INTERRUPTS();
1355 :
1356 66 : if (SlotSyncCtx->stopSignaled)
1357 : {
1358 2 : if (AmLogicalSlotSyncWorkerProcess())
1359 : {
1360 2 : ereport(LOG,
1361 : errmsg("replication slot synchronization worker will stop because promotion is triggered"));
1362 :
1363 2 : proc_exit(0);
1364 : }
1365 : else
1366 : {
1367 : /*
1368 : * For the backend executing SQL function
1369 : * pg_sync_replication_slots().
1370 : */
1371 0 : ereport(ERROR,
1372 : errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
1373 : errmsg("replication slot synchronization will stop because promotion is triggered"));
1374 : }
1375 : }
1376 :
1377 64 : if (ConfigReloadPending)
1378 2 : slotsync_reread_config();
1379 62 : }
1380 :
1381 : /*
1382 : * Connection cleanup function for slotsync worker.
1383 : *
1384 : * Called on slotsync worker exit.
1385 : */
1386 : static void
1387 8 : slotsync_worker_disconnect(int code, Datum arg)
1388 : {
1389 8 : WalReceiverConn *wrconn = (WalReceiverConn *) DatumGetPointer(arg);
1390 :
1391 8 : walrcv_disconnect(wrconn);
1392 8 : }
1393 :
1394 : /*
1395 : * Cleanup function for slotsync worker.
1396 : *
1397 : * Called on slotsync worker exit.
1398 : */
1399 : static void
1400 8 : slotsync_worker_onexit(int code, Datum arg)
1401 : {
1402 : /*
1403 : * We need to do slots cleanup here just like WalSndErrorCleanup() does.
1404 : *
1405 : * The startup process during promotion invokes ShutDownSlotSync() which
1406 : * waits for slot sync to finish and it does that by checking the
1407 : * 'syncing' flag. Thus the slot sync worker must be done with slots'
1408 : * release and cleanup to avoid any dangling temporary slots or active
1409 : * slots before it marks itself as finished syncing.
1410 : */
1411 :
1412 : /* Make sure active replication slots are released */
1413 8 : if (MyReplicationSlot != NULL)
1414 0 : ReplicationSlotRelease();
1415 :
1416 : /* Also cleanup the temporary slots. */
1417 8 : ReplicationSlotCleanup(false);
1418 :
1419 8 : SpinLockAcquire(&SlotSyncCtx->mutex);
1420 :
1421 8 : SlotSyncCtx->pid = InvalidPid;
1422 :
1423 : /*
1424 : * If syncing_slots is true, it indicates that the process errored out
1425 : * without resetting the flag. So, we need to clean up shared memory and
1426 : * reset the flag here.
1427 : */
1428 8 : if (syncing_slots)
1429 : {
1430 8 : SlotSyncCtx->syncing = false;
1431 8 : syncing_slots = false;
1432 : }
1433 :
1434 8 : SpinLockRelease(&SlotSyncCtx->mutex);
1435 8 : }
1436 :
1437 : /*
1438 : * Sleep for long enough that we believe it's likely that the slots on primary
1439 : * get updated.
1440 : *
1441 : * If there is no slot activity the wait time between sync-cycles will double
1442 : * (to a maximum of 30s). If there is some slot activity the wait time between
1443 : * sync-cycles is reset to the minimum (200ms).
1444 : */
1445 : static void
1446 28 : wait_for_slot_activity(bool some_slot_updated)
1447 : {
1448 : int rc;
1449 :
1450 28 : if (!some_slot_updated)
1451 : {
1452 : /*
1453 : * No slots were updated, so double the sleep time, but not beyond the
1454 : * maximum allowable value.
1455 : */
1456 12 : sleep_ms = Min(sleep_ms * 2, MAX_SLOTSYNC_WORKER_NAPTIME_MS);
1457 : }
1458 : else
1459 : {
1460 : /*
1461 : * Some slots were updated since the last sleep, so reset the sleep
1462 : * time.
1463 : */
1464 16 : sleep_ms = MIN_SLOTSYNC_WORKER_NAPTIME_MS;
1465 : }
1466 :
1467 28 : rc = WaitLatch(MyLatch,
1468 : WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
1469 : sleep_ms,
1470 : WAIT_EVENT_REPLICATION_SLOTSYNC_MAIN);
1471 :
1472 28 : if (rc & WL_LATCH_SET)
1473 8 : ResetLatch(MyLatch);
1474 28 : }
1475 :
1476 : /*
1477 : * Emit an error if a concurrent sync call is in progress.
1478 : * Otherwise, advertise that a sync is in progress.
1479 : */
1480 : static void
1481 26 : check_and_set_sync_info(pid_t sync_process_pid)
1482 : {
1483 26 : SpinLockAcquire(&SlotSyncCtx->mutex);
1484 :
1485 26 : if (SlotSyncCtx->syncing)
1486 : {
1487 0 : SpinLockRelease(&SlotSyncCtx->mutex);
1488 0 : ereport(ERROR,
1489 : errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
1490 : errmsg("cannot synchronize replication slots concurrently"));
1491 : }
1492 :
1493 : /* The pid must not be already assigned in SlotSyncCtx */
1494 : Assert(SlotSyncCtx->pid == InvalidPid);
1495 :
1496 26 : SlotSyncCtx->syncing = true;
1497 :
1498 : /*
1499 : * Advertise the required PID so that the startup process can kill the
1500 : * slot sync process on promotion.
1501 : */
1502 26 : SlotSyncCtx->pid = sync_process_pid;
1503 :
1504 26 : SpinLockRelease(&SlotSyncCtx->mutex);
1505 :
1506 26 : syncing_slots = true;
1507 26 : }
1508 :
1509 : /*
1510 : * Reset syncing flag.
1511 : */
1512 : static void
1513 18 : reset_syncing_flag(void)
1514 : {
1515 18 : SpinLockAcquire(&SlotSyncCtx->mutex);
1516 18 : SlotSyncCtx->syncing = false;
1517 18 : SlotSyncCtx->pid = InvalidPid;
1518 18 : SpinLockRelease(&SlotSyncCtx->mutex);
1519 :
1520 18 : syncing_slots = false;
1521 18 : }
1522 :
1523 : /*
1524 : * The main loop of our worker process.
1525 : *
1526 : * It connects to the primary server, fetches logical failover slots
1527 : * information periodically in order to create and sync the slots.
1528 : *
1529 : * Note: If any changes are made here, check if the corresponding SQL
1530 : * function logic in SyncReplicationSlots() also needs to be changed.
1531 : */
1532 : void
1533 8 : ReplSlotSyncWorkerMain(const void *startup_data, size_t startup_data_len)
1534 : {
1535 8 : WalReceiverConn *wrconn = NULL;
1536 : char *dbname;
1537 : char *err;
1538 : sigjmp_buf local_sigjmp_buf;
1539 : StringInfoData app_name;
1540 :
1541 : Assert(startup_data_len == 0);
1542 :
1543 8 : MyBackendType = B_SLOTSYNC_WORKER;
1544 :
1545 8 : init_ps_display(NULL);
1546 :
1547 : Assert(GetProcessingMode() == InitProcessing);
1548 :
1549 : /*
1550 : * Create a per-backend PGPROC struct in shared memory. We must do this
1551 : * before we access any shared memory.
1552 : */
1553 8 : InitProcess();
1554 :
1555 : /*
1556 : * Early initialization.
1557 : */
1558 8 : BaseInit();
1559 :
1560 : Assert(SlotSyncCtx != NULL);
1561 :
1562 : /*
1563 : * If an exception is encountered, processing resumes here.
1564 : *
1565 : * We just need to clean up, report the error, and go away.
1566 : *
1567 : * If we do not have this handling here, then since this worker process
1568 : * operates at the bottom of the exception stack, ERRORs turn into FATALs.
1569 : * Therefore, we create our own exception handler to catch ERRORs.
1570 : */
1571 8 : if (sigsetjmp(local_sigjmp_buf, 1) != 0)
1572 : {
1573 : /* since not using PG_TRY, must reset error stack by hand */
1574 0 : error_context_stack = NULL;
1575 :
1576 : /* Prevents interrupts while cleaning up */
1577 0 : HOLD_INTERRUPTS();
1578 :
1579 : /* Report the error to the server log */
1580 0 : EmitErrorReport();
1581 :
1582 : /*
1583 : * We can now go away. Note that because we called InitProcess, a
1584 : * callback was registered to do ProcKill, which will clean up
1585 : * necessary state.
1586 : */
1587 0 : proc_exit(0);
1588 : }
1589 :
1590 : /* We can now handle ereport(ERROR) */
1591 8 : PG_exception_stack = &local_sigjmp_buf;
1592 :
1593 : /* Setup signal handling */
1594 8 : pqsignal(SIGHUP, SignalHandlerForConfigReload);
1595 8 : pqsignal(SIGINT, StatementCancelHandler);
1596 8 : pqsignal(SIGTERM, die);
1597 8 : pqsignal(SIGFPE, FloatExceptionHandler);
1598 8 : pqsignal(SIGUSR1, procsignal_sigusr1_handler);
1599 8 : pqsignal(SIGUSR2, SIG_IGN);
1600 8 : pqsignal(SIGPIPE, SIG_IGN);
1601 8 : pqsignal(SIGCHLD, SIG_DFL);
1602 :
1603 8 : check_and_set_sync_info(MyProcPid);
1604 :
1605 8 : ereport(LOG, errmsg("slot sync worker started"));
1606 :
1607 : /* Register it as soon as SlotSyncCtx->pid is initialized. */
1608 8 : before_shmem_exit(slotsync_worker_onexit, (Datum) 0);
1609 :
1610 : /*
1611 : * Establishes SIGALRM handler and initialize timeout module. It is needed
1612 : * by InitPostgres to register different timeouts.
1613 : */
1614 8 : InitializeTimeouts();
1615 :
1616 : /* Load the libpq-specific functions */
1617 8 : load_file("libpqwalreceiver", false);
1618 :
1619 : /*
1620 : * Unblock signals (they were blocked when the postmaster forked us)
1621 : */
1622 8 : sigprocmask(SIG_SETMASK, &UnBlockSig, NULL);
1623 :
1624 : /*
1625 : * Set always-secure search path, so malicious users can't redirect user
1626 : * code (e.g. operators).
1627 : *
1628 : * It's not strictly necessary since we won't be scanning or writing to
1629 : * any user table locally, but it's good to retain it here for added
1630 : * precaution.
1631 : */
1632 8 : SetConfigOption("search_path", "", PGC_SUSET, PGC_S_OVERRIDE);
1633 :
1634 8 : dbname = CheckAndGetDbnameFromConninfo();
1635 :
1636 : /*
1637 : * Connect to the database specified by the user in primary_conninfo. We
1638 : * need a database connection for walrcv_exec to work which we use to
1639 : * fetch slot information from the remote node. See comments atop
1640 : * libpqrcv_exec.
1641 : *
1642 : * We do not specify a specific user here since the slot sync worker will
1643 : * operate as a superuser. This is safe because the slot sync worker does
1644 : * not interact with user tables, eliminating the risk of executing
1645 : * arbitrary code within triggers.
1646 : */
1647 8 : InitPostgres(dbname, InvalidOid, NULL, InvalidOid, 0, NULL);
1648 :
1649 8 : SetProcessingMode(NormalProcessing);
1650 :
1651 8 : initStringInfo(&app_name);
1652 8 : if (cluster_name[0])
1653 8 : appendStringInfo(&app_name, "%s_%s", cluster_name, "slotsync worker");
1654 : else
1655 0 : appendStringInfoString(&app_name, "slotsync worker");
1656 :
1657 : /*
1658 : * Establish the connection to the primary server for slot
1659 : * synchronization.
1660 : */
1661 8 : wrconn = walrcv_connect(PrimaryConnInfo, false, false, false,
1662 : app_name.data, &err);
1663 :
1664 8 : if (!wrconn)
1665 0 : ereport(ERROR,
1666 : errcode(ERRCODE_CONNECTION_FAILURE),
1667 : errmsg("synchronization worker \"%s\" could not connect to the primary server: %s",
1668 : app_name.data, err));
1669 :
1670 8 : pfree(app_name.data);
1671 :
1672 : /*
1673 : * Register the disconnection callback.
1674 : *
1675 : * XXX: This can be combined with previous cleanup registration of
1676 : * slotsync_worker_onexit() but that will need the connection to be made
1677 : * global and we want to avoid introducing global for this purpose.
1678 : */
1679 8 : before_shmem_exit(slotsync_worker_disconnect, PointerGetDatum(wrconn));
1680 :
1681 : /*
1682 : * Using the specified primary server connection, check that we are not a
1683 : * cascading standby and slot configured in 'primary_slot_name' exists on
1684 : * the primary server.
1685 : */
1686 8 : validate_remote_info(wrconn);
1687 :
1688 : /* Main loop to synchronize slots */
1689 : for (;;)
1690 26 : {
1691 34 : bool some_slot_updated = false;
1692 34 : bool started_tx = false;
1693 : List *remote_slots;
1694 :
1695 34 : ProcessSlotSyncInterrupts();
1696 :
1697 : /*
1698 : * The syscache access in fetch_remote_slots() needs a transaction
1699 : * env.
1700 : */
1701 26 : if (!IsTransactionState())
1702 : {
1703 26 : StartTransactionCommand();
1704 26 : started_tx = true;
1705 : }
1706 :
1707 26 : remote_slots = fetch_remote_slots(wrconn, NIL);
1708 26 : some_slot_updated = synchronize_slots(wrconn, remote_slots, NULL);
1709 26 : list_free_deep(remote_slots);
1710 :
1711 26 : if (started_tx)
1712 26 : CommitTransactionCommand();
1713 :
1714 26 : wait_for_slot_activity(some_slot_updated);
1715 : }
1716 :
1717 : /*
1718 : * The slot sync worker can't get here because it will only stop when it
1719 : * receives a stop request from the startup process, or when there is an
1720 : * error.
1721 : */
1722 : Assert(false);
1723 : }
1724 :
1725 : /*
1726 : * Update the inactive_since property for synced slots.
1727 : *
1728 : * Note that this function is currently called when we shutdown the slot
1729 : * sync machinery.
1730 : */
1731 : static void
1732 1856 : update_synced_slots_inactive_since(void)
1733 : {
1734 1856 : TimestampTz now = 0;
1735 :
1736 : /*
1737 : * We need to update inactive_since only when we are promoting standby to
1738 : * correctly interpret the inactive_since if the standby gets promoted
1739 : * without a restart. We don't want the slots to appear inactive for a
1740 : * long time after promotion if they haven't been synchronized recently.
1741 : * Whoever acquires the slot, i.e., makes the slot active, will reset it.
1742 : */
1743 1856 : if (!StandbyMode)
1744 1752 : return;
1745 :
1746 : /* The slot sync worker or the SQL function mustn't be running by now */
1747 : Assert((SlotSyncCtx->pid == InvalidPid) && !SlotSyncCtx->syncing);
1748 :
1749 104 : LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
1750 :
1751 1120 : for (int i = 0; i < max_replication_slots; i++)
1752 : {
1753 1016 : ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
1754 :
1755 : /* Check if it is a synchronized slot */
1756 1016 : if (s->in_use && s->data.synced)
1757 : {
1758 : Assert(SlotIsLogical(s));
1759 :
1760 : /* The slot must not be acquired by any process */
1761 : Assert(s->active_pid == 0);
1762 :
1763 : /* Use the same inactive_since time for all the slots. */
1764 6 : if (now == 0)
1765 4 : now = GetCurrentTimestamp();
1766 :
1767 6 : ReplicationSlotSetInactiveSince(s, now, true);
1768 : }
1769 : }
1770 :
1771 104 : LWLockRelease(ReplicationSlotControlLock);
1772 : }
1773 :
1774 : /*
1775 : * Shut down slot synchronization.
1776 : *
1777 : * This function sets stopSignaled=true and wakes up the slot sync process
1778 : * (either worker or backend running the SQL function pg_sync_replication_slots())
1779 : * so that worker can exit or the SQL function pg_sync_replication_slots() can
1780 : * finish. It also waits till the slot sync worker has exited or
1781 : * pg_sync_replication_slots() has finished.
1782 : */
1783 : void
1784 1856 : ShutDownSlotSync(void)
1785 : {
1786 : pid_t sync_process_pid;
1787 :
1788 1856 : SpinLockAcquire(&SlotSyncCtx->mutex);
1789 :
1790 1856 : SlotSyncCtx->stopSignaled = true;
1791 :
1792 : /*
1793 : * Return if neither the slot sync worker is running nor the function
1794 : * pg_sync_replication_slots() is executing.
1795 : */
1796 1856 : if (!SlotSyncCtx->syncing)
1797 : {
1798 1854 : SpinLockRelease(&SlotSyncCtx->mutex);
1799 1854 : update_synced_slots_inactive_since();
1800 1854 : return;
1801 : }
1802 :
1803 2 : sync_process_pid = SlotSyncCtx->pid;
1804 :
1805 2 : SpinLockRelease(&SlotSyncCtx->mutex);
1806 :
1807 : /*
1808 : * Signal process doing slotsync, if any. The process will stop upon
1809 : * detecting that the stopSignaled flag is set to true.
1810 : */
1811 2 : if (sync_process_pid != InvalidPid)
1812 2 : kill(sync_process_pid, SIGUSR1);
1813 :
1814 : /* Wait for slot sync to end */
1815 : for (;;)
1816 0 : {
1817 : int rc;
1818 :
1819 : /* Wait a bit, we don't expect to have to wait long */
1820 2 : rc = WaitLatch(MyLatch,
1821 : WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
1822 : 10L, WAIT_EVENT_REPLICATION_SLOTSYNC_SHUTDOWN);
1823 :
1824 2 : if (rc & WL_LATCH_SET)
1825 : {
1826 0 : ResetLatch(MyLatch);
1827 0 : CHECK_FOR_INTERRUPTS();
1828 : }
1829 :
1830 2 : SpinLockAcquire(&SlotSyncCtx->mutex);
1831 :
1832 : /* Ensure that no process is syncing the slots. */
1833 2 : if (!SlotSyncCtx->syncing)
1834 2 : break;
1835 :
1836 0 : SpinLockRelease(&SlotSyncCtx->mutex);
1837 : }
1838 :
1839 2 : SpinLockRelease(&SlotSyncCtx->mutex);
1840 :
1841 2 : update_synced_slots_inactive_since();
1842 : }
1843 :
1844 : /*
1845 : * SlotSyncWorkerCanRestart
1846 : *
1847 : * Return true, indicating worker is allowed to restart, if enough time has
1848 : * passed since it was last launched to reach SLOTSYNC_RESTART_INTERVAL_SEC.
1849 : * Otherwise return false.
1850 : *
1851 : * This is a safety valve to protect against continuous respawn attempts if the
1852 : * worker is dying immediately at launch. Note that since we will retry to
1853 : * launch the worker from the postmaster main loop, we will get another
1854 : * chance later.
1855 : */
1856 : bool
1857 12 : SlotSyncWorkerCanRestart(void)
1858 : {
1859 12 : time_t curtime = time(NULL);
1860 :
1861 : /*
1862 : * If first time through, or time somehow went backwards, always update
1863 : * last_start_time to match the current clock and allow worker start.
1864 : * Otherwise allow it only once enough time has elapsed.
1865 : */
1866 12 : if (SlotSyncCtx->last_start_time == 0 ||
1867 4 : curtime < SlotSyncCtx->last_start_time ||
1868 4 : curtime - SlotSyncCtx->last_start_time >= SLOTSYNC_RESTART_INTERVAL_SEC)
1869 : {
1870 8 : SlotSyncCtx->last_start_time = curtime;
1871 8 : return true;
1872 : }
1873 4 : return false;
1874 : }
1875 :
1876 : /*
1877 : * Is current process syncing replication slots?
1878 : *
1879 : * Could be either backend executing SQL function or slot sync worker.
1880 : */
1881 : bool
1882 48 : IsSyncingReplicationSlots(void)
1883 : {
1884 48 : return syncing_slots;
1885 : }
1886 :
1887 : /*
1888 : * Amount of shared memory required for slot synchronization.
1889 : */
1890 : Size
1891 6510 : SlotSyncShmemSize(void)
1892 : {
1893 6510 : return sizeof(SlotSyncCtxStruct);
1894 : }
1895 :
1896 : /*
1897 : * Allocate and initialize the shared memory of slot synchronization.
1898 : */
1899 : void
1900 2272 : SlotSyncShmemInit(void)
1901 : {
1902 2272 : Size size = SlotSyncShmemSize();
1903 : bool found;
1904 :
1905 2272 : SlotSyncCtx = (SlotSyncCtxStruct *)
1906 2272 : ShmemInitStruct("Slot Sync Data", size, &found);
1907 :
1908 2272 : if (!found)
1909 : {
1910 2272 : memset(SlotSyncCtx, 0, size);
1911 2272 : SlotSyncCtx->pid = InvalidPid;
1912 2272 : SpinLockInit(&SlotSyncCtx->mutex);
1913 : }
1914 2272 : }
1915 :
1916 : /*
1917 : * Error cleanup callback for slot sync SQL function.
1918 : */
1919 : static void
1920 2 : slotsync_failure_callback(int code, Datum arg)
1921 : {
1922 2 : WalReceiverConn *wrconn = (WalReceiverConn *) DatumGetPointer(arg);
1923 :
1924 : /*
1925 : * We need to do slots cleanup here just like WalSndErrorCleanup() does.
1926 : *
1927 : * The startup process during promotion invokes ShutDownSlotSync() which
1928 : * waits for slot sync to finish and it does that by checking the
1929 : * 'syncing' flag. Thus the SQL function must be done with slots' release
1930 : * and cleanup to avoid any dangling temporary slots or active slots
1931 : * before it marks itself as finished syncing.
1932 : */
1933 :
1934 : /* Make sure active replication slots are released */
1935 2 : if (MyReplicationSlot != NULL)
1936 0 : ReplicationSlotRelease();
1937 :
1938 : /* Also cleanup the synced temporary slots. */
1939 2 : ReplicationSlotCleanup(true);
1940 :
1941 : /*
1942 : * The set syncing_slots indicates that the process errored out without
1943 : * resetting the flag. So, we need to clean up shared memory and reset the
1944 : * flag here.
1945 : */
1946 2 : if (syncing_slots)
1947 2 : reset_syncing_flag();
1948 :
1949 2 : walrcv_disconnect(wrconn);
1950 2 : }
1951 :
1952 : /*
1953 : * Helper function to extract slot names from a list of remote slots
1954 : */
1955 : static List *
1956 2 : extract_slot_names(List *remote_slots)
1957 : {
1958 2 : List *slot_names = NIL;
1959 :
1960 6 : foreach_ptr(RemoteSlot, remote_slot, remote_slots)
1961 : {
1962 : char *slot_name;
1963 :
1964 2 : slot_name = pstrdup(remote_slot->name);
1965 2 : slot_names = lappend(slot_names, slot_name);
1966 : }
1967 :
1968 2 : return slot_names;
1969 : }
1970 :
1971 : /*
1972 : * Synchronize the failover enabled replication slots using the specified
1973 : * primary server connection.
1974 : *
1975 : * Repeatedly fetches and updates replication slot information from the
1976 : * primary until all slots are at least "sync ready".
1977 : *
1978 : * Exits early if promotion is triggered or certain critical
1979 : * configuration parameters have changed.
1980 : */
1981 : void
1982 18 : SyncReplicationSlots(WalReceiverConn *wrconn)
1983 : {
1984 18 : PG_ENSURE_ERROR_CLEANUP(slotsync_failure_callback, PointerGetDatum(wrconn));
1985 : {
1986 18 : List *remote_slots = NIL;
1987 18 : List *slot_names = NIL; /* List of slot names to track */
1988 :
1989 18 : check_and_set_sync_info(MyProcPid);
1990 :
1991 : /* Check for interrupts and config changes */
1992 18 : ProcessSlotSyncInterrupts();
1993 :
1994 18 : validate_remote_info(wrconn);
1995 :
1996 : /* Retry until all the slots are sync-ready */
1997 : for (;;)
1998 2 : {
1999 18 : bool slot_persistence_pending = false;
2000 18 : bool some_slot_updated = false;
2001 :
2002 : /* Check for interrupts and config changes */
2003 18 : ProcessSlotSyncInterrupts();
2004 :
2005 : /* We must be in a valid transaction state */
2006 : Assert(IsTransactionState());
2007 :
2008 : /*
2009 : * Fetch remote slot info for the given slot_names. If slot_names
2010 : * is NIL, fetch all failover-enabled slots. Note that we reuse
2011 : * slot_names from the first iteration; re-fetching all failover
2012 : * slots each time could cause an endless loop. Instead of
2013 : * reprocessing only the pending slots in each iteration, it's
2014 : * better to process all the slots received in the first
2015 : * iteration. This ensures that by the time we're done, all slots
2016 : * reflect the latest values.
2017 : */
2018 18 : remote_slots = fetch_remote_slots(wrconn, slot_names);
2019 :
2020 : /* Attempt to synchronize slots */
2021 18 : some_slot_updated = synchronize_slots(wrconn, remote_slots,
2022 : &slot_persistence_pending);
2023 :
2024 : /*
2025 : * If slot_persistence_pending is true, extract slot names for
2026 : * future iterations (only needed if we haven't done it yet)
2027 : */
2028 18 : if (slot_names == NIL && slot_persistence_pending)
2029 2 : slot_names = extract_slot_names(remote_slots);
2030 :
2031 : /* Free the current remote_slots list */
2032 18 : list_free_deep(remote_slots);
2033 :
2034 : /* Done if all slots are persisted i.e are sync-ready */
2035 18 : if (!slot_persistence_pending)
2036 16 : break;
2037 :
2038 : /* wait before retrying again */
2039 2 : wait_for_slot_activity(some_slot_updated);
2040 : }
2041 :
2042 16 : if (slot_names)
2043 2 : list_free_deep(slot_names);
2044 :
2045 : /* Cleanup the synced temporary slots */
2046 16 : ReplicationSlotCleanup(true);
2047 :
2048 : /* We are done with sync, so reset sync flag */
2049 16 : reset_syncing_flag();
2050 : }
2051 18 : PG_END_ENSURE_ERROR_CLEANUP(slotsync_failure_callback, PointerGetDatum(wrconn));
2052 16 : }
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