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) 2024-2025, 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 : * Any standby synchronized slots will be dropped if they no longer need
43 : * to be synchronized. See comment atop drop_local_obsolete_slots() for more
44 : * details.
45 : *---------------------------------------------------------------------------
46 : */
47 :
48 : #include "postgres.h"
49 :
50 : #include <time.h>
51 :
52 : #include "access/xlog_internal.h"
53 : #include "access/xlogrecovery.h"
54 : #include "catalog/pg_database.h"
55 : #include "libpq/pqsignal.h"
56 : #include "pgstat.h"
57 : #include "postmaster/interrupt.h"
58 : #include "replication/logical.h"
59 : #include "replication/slotsync.h"
60 : #include "replication/snapbuild.h"
61 : #include "storage/ipc.h"
62 : #include "storage/lmgr.h"
63 : #include "storage/proc.h"
64 : #include "storage/procarray.h"
65 : #include "tcop/tcopprot.h"
66 : #include "utils/builtins.h"
67 : #include "utils/pg_lsn.h"
68 : #include "utils/ps_status.h"
69 : #include "utils/timeout.h"
70 :
71 : /*
72 : * Struct for sharing information to control slot synchronization.
73 : *
74 : * The slot sync worker's pid is needed by the startup process to shut it
75 : * down during promotion. The startup process shuts down the slot sync worker
76 : * and also sets stopSignaled=true to handle the race condition when the
77 : * postmaster has not noticed the promotion yet and thus may end up restarting
78 : * the slot sync worker. If stopSignaled is set, the worker will exit in such a
79 : * case. The SQL function pg_sync_replication_slots() will also error out if
80 : * this flag is set. Note that we don't need to reset this variable as after
81 : * promotion the slot sync worker won't be restarted because the pmState
82 : * changes to PM_RUN from PM_HOT_STANDBY and we don't support demoting
83 : * primary without restarting the server. See LaunchMissingBackgroundProcesses.
84 : *
85 : * The 'syncing' flag is needed to prevent concurrent slot syncs to avoid slot
86 : * overwrites.
87 : *
88 : * The 'last_start_time' is needed by postmaster to start the slot sync worker
89 : * once per SLOTSYNC_RESTART_INTERVAL_SEC. In cases where an immediate restart
90 : * is expected (e.g., slot sync GUCs change), slot sync worker will reset
91 : * last_start_time before exiting, so that postmaster can start the worker
92 : * without waiting for SLOTSYNC_RESTART_INTERVAL_SEC.
93 : */
94 : typedef struct SlotSyncCtxStruct
95 : {
96 : pid_t pid;
97 : bool stopSignaled;
98 : bool syncing;
99 : time_t last_start_time;
100 : slock_t mutex;
101 : } SlotSyncCtxStruct;
102 :
103 : static SlotSyncCtxStruct *SlotSyncCtx = NULL;
104 :
105 : /* GUC variable */
106 : bool sync_replication_slots = false;
107 :
108 : /*
109 : * The sleep time (ms) between slot-sync cycles varies dynamically
110 : * (within a MIN/MAX range) according to slot activity. See
111 : * wait_for_slot_activity() for details.
112 : */
113 : #define MIN_SLOTSYNC_WORKER_NAPTIME_MS 200
114 : #define MAX_SLOTSYNC_WORKER_NAPTIME_MS 30000 /* 30s */
115 :
116 : static long sleep_ms = MIN_SLOTSYNC_WORKER_NAPTIME_MS;
117 :
118 : /* The restart interval for slot sync work used by postmaster */
119 : #define SLOTSYNC_RESTART_INTERVAL_SEC 10
120 :
121 : /*
122 : * Flag to tell if we are syncing replication slots. Unlike the 'syncing' flag
123 : * in SlotSyncCtxStruct, this flag is true only if the current process is
124 : * performing slot synchronization.
125 : */
126 : static bool syncing_slots = false;
127 :
128 : /*
129 : * Structure to hold information fetched from the primary server about a logical
130 : * replication slot.
131 : */
132 : typedef struct RemoteSlot
133 : {
134 : char *name;
135 : char *plugin;
136 : char *database;
137 : bool two_phase;
138 : bool failover;
139 : XLogRecPtr restart_lsn;
140 : XLogRecPtr confirmed_lsn;
141 : XLogRecPtr two_phase_at;
142 : TransactionId catalog_xmin;
143 :
144 : /* RS_INVAL_NONE if valid, or the reason of invalidation */
145 : ReplicationSlotInvalidationCause invalidated;
146 : } RemoteSlot;
147 :
148 : static void slotsync_failure_callback(int code, Datum arg);
149 : static void update_synced_slots_inactive_since(void);
150 :
151 : /*
152 : * If necessary, update the local synced slot's metadata based on the data
153 : * from the remote slot.
154 : *
155 : * If no update was needed (the data of the remote slot is the same as the
156 : * local slot) return false, otherwise true.
157 : *
158 : * *found_consistent_snapshot will be true iff the remote slot's LSN or xmin is
159 : * modified, and decoding from the corresponding LSN's can reach a
160 : * consistent snapshot.
161 : *
162 : * *remote_slot_precedes will be true if the remote slot's LSN or xmin
163 : * precedes locally reserved position.
164 : */
165 : static bool
166 78 : update_local_synced_slot(RemoteSlot *remote_slot, Oid remote_dbid,
167 : bool *found_consistent_snapshot,
168 : bool *remote_slot_precedes)
169 : {
170 78 : ReplicationSlot *slot = MyReplicationSlot;
171 78 : bool updated_xmin_or_lsn = false;
172 78 : bool updated_config = false;
173 :
174 : Assert(slot->data.invalidated == RS_INVAL_NONE);
175 :
176 78 : if (found_consistent_snapshot)
177 10 : *found_consistent_snapshot = false;
178 :
179 78 : if (remote_slot_precedes)
180 10 : *remote_slot_precedes = false;
181 :
182 : /*
183 : * Don't overwrite if we already have a newer catalog_xmin and
184 : * restart_lsn.
185 : */
186 156 : if (remote_slot->restart_lsn < slot->data.restart_lsn ||
187 78 : TransactionIdPrecedes(remote_slot->catalog_xmin,
188 : slot->data.catalog_xmin))
189 : {
190 : /*
191 : * This can happen in following situations:
192 : *
193 : * If the slot is temporary, it means either the initial WAL location
194 : * reserved for the local slot is ahead of the remote slot's
195 : * restart_lsn or the initial xmin_horizon computed for the local slot
196 : * is ahead of the remote slot.
197 : *
198 : * If the slot is persistent, both restart_lsn and catalog_xmin of the
199 : * synced slot could still be ahead of the remote slot. Since we use
200 : * slot advance functionality to keep snapbuild/slot updated, it is
201 : * possible that the restart_lsn and catalog_xmin are advanced to a
202 : * later position than it has on the primary. This can happen when
203 : * slot advancing machinery finds running xacts record after reaching
204 : * the consistent state at a later point than the primary where it
205 : * serializes the snapshot and updates the restart_lsn.
206 : *
207 : * We LOG the message if the slot is temporary as it can help the user
208 : * to understand why the slot is not sync-ready. In the case of a
209 : * persistent slot, it would be a more common case and won't directly
210 : * impact the users, so we used DEBUG1 level to log the message.
211 : */
212 0 : ereport(slot->data.persistency == RS_TEMPORARY ? LOG : DEBUG1,
213 : errmsg("could not synchronize replication slot \"%s\"",
214 : remote_slot->name),
215 : 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.",
216 : LSN_FORMAT_ARGS(remote_slot->restart_lsn),
217 : remote_slot->catalog_xmin,
218 : LSN_FORMAT_ARGS(slot->data.restart_lsn),
219 : slot->data.catalog_xmin));
220 :
221 0 : if (remote_slot_precedes)
222 0 : *remote_slot_precedes = true;
223 :
224 : /*
225 : * Skip updating the configuration. This is required to avoid syncing
226 : * two_phase_at without syncing confirmed_lsn. Otherwise, the prepared
227 : * transaction between old confirmed_lsn and two_phase_at will
228 : * unexpectedly get decoded and sent to the downstream after
229 : * promotion. See comments in ReorderBufferFinishPrepared.
230 : */
231 0 : return false;
232 : }
233 :
234 : /*
235 : * Attempt to sync LSNs and xmins only if remote slot is ahead of local
236 : * slot.
237 : */
238 78 : if (remote_slot->confirmed_lsn > slot->data.confirmed_flush ||
239 114 : remote_slot->restart_lsn > slot->data.restart_lsn ||
240 56 : TransactionIdFollows(remote_slot->catalog_xmin,
241 : slot->data.catalog_xmin))
242 : {
243 : /*
244 : * We can't directly copy the remote slot's LSN or xmin unless there
245 : * exists a consistent snapshot at that point. Otherwise, after
246 : * promotion, the slots may not reach a consistent point before the
247 : * confirmed_flush_lsn which can lead to a data loss. To avoid data
248 : * loss, we let slot machinery advance the slot which ensures that
249 : * snapbuilder/slot statuses are updated properly.
250 : */
251 22 : if (SnapBuildSnapshotExists(remote_slot->restart_lsn))
252 : {
253 : /*
254 : * Update the slot info directly if there is a serialized snapshot
255 : * at the restart_lsn, as the slot can quickly reach consistency
256 : * at restart_lsn by restoring the snapshot.
257 : */
258 4 : SpinLockAcquire(&slot->mutex);
259 4 : slot->data.restart_lsn = remote_slot->restart_lsn;
260 4 : slot->data.confirmed_flush = remote_slot->confirmed_lsn;
261 4 : slot->data.catalog_xmin = remote_slot->catalog_xmin;
262 4 : SpinLockRelease(&slot->mutex);
263 :
264 4 : if (found_consistent_snapshot)
265 0 : *found_consistent_snapshot = true;
266 : }
267 : else
268 : {
269 18 : LogicalSlotAdvanceAndCheckSnapState(remote_slot->confirmed_lsn,
270 : found_consistent_snapshot);
271 :
272 : /* Sanity check */
273 18 : if (slot->data.confirmed_flush != remote_slot->confirmed_lsn)
274 0 : ereport(ERROR,
275 : errmsg_internal("synchronized confirmed_flush for slot \"%s\" differs from remote slot",
276 : remote_slot->name),
277 : errdetail_internal("Remote slot has LSN %X/%08X but local slot has LSN %X/%08X.",
278 : LSN_FORMAT_ARGS(remote_slot->confirmed_lsn),
279 : LSN_FORMAT_ARGS(slot->data.confirmed_flush)));
280 : }
281 :
282 22 : updated_xmin_or_lsn = true;
283 : }
284 :
285 78 : if (remote_dbid != slot->data.database ||
286 78 : remote_slot->two_phase != slot->data.two_phase ||
287 76 : remote_slot->failover != slot->data.failover ||
288 76 : strcmp(remote_slot->plugin, NameStr(slot->data.plugin)) != 0 ||
289 76 : remote_slot->two_phase_at != slot->data.two_phase_at)
290 : {
291 : NameData plugin_name;
292 :
293 : /* Avoid expensive operations while holding a spinlock. */
294 2 : namestrcpy(&plugin_name, remote_slot->plugin);
295 :
296 2 : SpinLockAcquire(&slot->mutex);
297 2 : slot->data.plugin = plugin_name;
298 2 : slot->data.database = remote_dbid;
299 2 : slot->data.two_phase = remote_slot->two_phase;
300 2 : slot->data.two_phase_at = remote_slot->two_phase_at;
301 2 : slot->data.failover = remote_slot->failover;
302 2 : SpinLockRelease(&slot->mutex);
303 :
304 2 : updated_config = true;
305 :
306 : /*
307 : * Ensure that there is no risk of sending prepared transactions
308 : * unexpectedly after the promotion.
309 : */
310 : Assert(slot->data.two_phase_at <= slot->data.confirmed_flush);
311 : }
312 :
313 : /*
314 : * We have to write the changed xmin to disk *before* we change the
315 : * in-memory value, otherwise after a crash we wouldn't know that some
316 : * catalog tuples might have been removed already.
317 : */
318 78 : if (updated_config || updated_xmin_or_lsn)
319 : {
320 24 : ReplicationSlotMarkDirty();
321 24 : ReplicationSlotSave();
322 : }
323 :
324 : /*
325 : * Now the new xmin is safely on disk, we can let the global value
326 : * advance. We do not take ProcArrayLock or similar since we only advance
327 : * xmin here and there's not much harm done by a concurrent computation
328 : * missing that.
329 : */
330 78 : if (updated_xmin_or_lsn)
331 : {
332 22 : SpinLockAcquire(&slot->mutex);
333 22 : slot->effective_catalog_xmin = remote_slot->catalog_xmin;
334 22 : SpinLockRelease(&slot->mutex);
335 :
336 22 : ReplicationSlotsComputeRequiredXmin(false);
337 22 : ReplicationSlotsComputeRequiredLSN();
338 : }
339 :
340 78 : return updated_config || updated_xmin_or_lsn;
341 : }
342 :
343 : /*
344 : * Get the list of local logical slots that are synchronized from the
345 : * primary server.
346 : */
347 : static List *
348 42 : get_local_synced_slots(void)
349 : {
350 42 : List *local_slots = NIL;
351 :
352 42 : LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
353 :
354 462 : for (int i = 0; i < max_replication_slots; i++)
355 : {
356 420 : ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
357 :
358 : /* Check if it is a synchronized slot */
359 420 : if (s->in_use && s->data.synced)
360 : {
361 : Assert(SlotIsLogical(s));
362 72 : local_slots = lappend(local_slots, s);
363 : }
364 : }
365 :
366 42 : LWLockRelease(ReplicationSlotControlLock);
367 :
368 42 : return local_slots;
369 : }
370 :
371 : /*
372 : * Helper function to check if local_slot is required to be retained.
373 : *
374 : * Return false either if local_slot does not exist in the remote_slots list
375 : * or is invalidated while the corresponding remote slot is still valid,
376 : * otherwise true.
377 : */
378 : static bool
379 72 : local_sync_slot_required(ReplicationSlot *local_slot, List *remote_slots)
380 : {
381 72 : bool remote_exists = false;
382 72 : bool locally_invalidated = false;
383 :
384 178 : foreach_ptr(RemoteSlot, remote_slot, remote_slots)
385 : {
386 104 : if (strcmp(remote_slot->name, NameStr(local_slot->data.name)) == 0)
387 : {
388 70 : remote_exists = true;
389 :
390 : /*
391 : * If remote slot is not invalidated but local slot is marked as
392 : * invalidated, then set locally_invalidated flag.
393 : */
394 70 : SpinLockAcquire(&local_slot->mutex);
395 70 : locally_invalidated =
396 140 : (remote_slot->invalidated == RS_INVAL_NONE) &&
397 70 : (local_slot->data.invalidated != RS_INVAL_NONE);
398 70 : SpinLockRelease(&local_slot->mutex);
399 :
400 70 : break;
401 : }
402 : }
403 :
404 72 : return (remote_exists && !locally_invalidated);
405 : }
406 :
407 : /*
408 : * Drop local obsolete slots.
409 : *
410 : * Drop the local slots that no longer need to be synced i.e. these either do
411 : * not exist on the primary or are no longer enabled for failover.
412 : *
413 : * Additionally, drop any slots that are valid on the primary but got
414 : * invalidated on the standby. This situation may occur due to the following
415 : * reasons:
416 : * - The 'max_slot_wal_keep_size' on the standby is insufficient to retain WAL
417 : * records from the restart_lsn of the slot.
418 : * - 'primary_slot_name' is temporarily reset to null and the physical slot is
419 : * removed.
420 : * These dropped slots will get recreated in next sync-cycle and it is okay to
421 : * drop and recreate such slots as long as these are not consumable on the
422 : * standby (which is the case currently).
423 : *
424 : * Note: Change of 'wal_level' on the primary server to a level lower than
425 : * logical may also result in slot invalidation and removal on the standby.
426 : * This is because such 'wal_level' change is only possible if the logical
427 : * slots are removed on the primary server, so it's expected to see the
428 : * slots being invalidated and removed on the standby too (and re-created
429 : * if they are re-created on the primary server).
430 : */
431 : static void
432 42 : drop_local_obsolete_slots(List *remote_slot_list)
433 : {
434 42 : List *local_slots = get_local_synced_slots();
435 :
436 156 : foreach_ptr(ReplicationSlot, local_slot, local_slots)
437 : {
438 : /* Drop the local slot if it is not required to be retained. */
439 72 : if (!local_sync_slot_required(local_slot, remote_slot_list))
440 : {
441 : bool synced_slot;
442 :
443 : /*
444 : * Use shared lock to prevent a conflict with
445 : * ReplicationSlotsDropDBSlots(), trying to drop the same slot
446 : * during a drop-database operation.
447 : */
448 4 : LockSharedObject(DatabaseRelationId, local_slot->data.database,
449 : 0, AccessShareLock);
450 :
451 : /*
452 : * In the small window between getting the slot to drop and
453 : * locking the database, there is a possibility of a parallel
454 : * database drop by the startup process and the creation of a new
455 : * slot by the user. This new user-created slot may end up using
456 : * the same shared memory as that of 'local_slot'. Thus check if
457 : * local_slot is still the synced one before performing actual
458 : * drop.
459 : */
460 4 : SpinLockAcquire(&local_slot->mutex);
461 4 : synced_slot = local_slot->in_use && local_slot->data.synced;
462 4 : SpinLockRelease(&local_slot->mutex);
463 :
464 4 : if (synced_slot)
465 : {
466 4 : ReplicationSlotAcquire(NameStr(local_slot->data.name), true, false);
467 4 : ReplicationSlotDropAcquired();
468 : }
469 :
470 4 : UnlockSharedObject(DatabaseRelationId, local_slot->data.database,
471 : 0, AccessShareLock);
472 :
473 4 : ereport(LOG,
474 : errmsg("dropped replication slot \"%s\" of database with OID %u",
475 : NameStr(local_slot->data.name),
476 : local_slot->data.database));
477 : }
478 : }
479 42 : }
480 :
481 : /*
482 : * Reserve WAL for the currently active local slot using the specified WAL
483 : * location (restart_lsn).
484 : *
485 : * If the given WAL location has been removed, reserve WAL using the oldest
486 : * existing WAL segment.
487 : */
488 : static void
489 10 : reserve_wal_for_local_slot(XLogRecPtr restart_lsn)
490 : {
491 : XLogSegNo oldest_segno;
492 : XLogSegNo segno;
493 10 : ReplicationSlot *slot = MyReplicationSlot;
494 :
495 : Assert(slot != NULL);
496 : Assert(XLogRecPtrIsInvalid(slot->data.restart_lsn));
497 :
498 : while (true)
499 : {
500 10 : SpinLockAcquire(&slot->mutex);
501 10 : slot->data.restart_lsn = restart_lsn;
502 10 : SpinLockRelease(&slot->mutex);
503 :
504 : /* Prevent WAL removal as fast as possible */
505 10 : ReplicationSlotsComputeRequiredLSN();
506 :
507 10 : XLByteToSeg(slot->data.restart_lsn, segno, wal_segment_size);
508 :
509 : /*
510 : * Find the oldest existing WAL segment file.
511 : *
512 : * Normally, we can determine it by using the last removed segment
513 : * number. However, if no WAL segment files have been removed by a
514 : * checkpoint since startup, we need to search for the oldest segment
515 : * file from the current timeline existing in XLOGDIR.
516 : *
517 : * XXX: Currently, we are searching for the oldest segment in the
518 : * current timeline as there is less chance of the slot's restart_lsn
519 : * from being some prior timeline, and even if it happens, in the
520 : * worst case, we will wait to sync till the slot's restart_lsn moved
521 : * to the current timeline.
522 : */
523 10 : oldest_segno = XLogGetLastRemovedSegno() + 1;
524 :
525 10 : if (oldest_segno == 1)
526 : {
527 : TimeLineID cur_timeline;
528 :
529 6 : GetWalRcvFlushRecPtr(NULL, &cur_timeline);
530 6 : oldest_segno = XLogGetOldestSegno(cur_timeline);
531 : }
532 :
533 10 : elog(DEBUG1, "segno: " UINT64_FORMAT " of purposed restart_lsn for the synced slot, oldest_segno: " UINT64_FORMAT " available",
534 : segno, oldest_segno);
535 :
536 : /*
537 : * If all required WAL is still there, great, otherwise retry. The
538 : * slot should prevent further removal of WAL, unless there's a
539 : * concurrent ReplicationSlotsComputeRequiredLSN() after we've written
540 : * the new restart_lsn above, so normally we should never need to loop
541 : * more than twice.
542 : */
543 10 : if (segno >= oldest_segno)
544 10 : break;
545 :
546 : /* Retry using the location of the oldest wal segment */
547 0 : XLogSegNoOffsetToRecPtr(oldest_segno, 0, wal_segment_size, restart_lsn);
548 : }
549 10 : }
550 :
551 : /*
552 : * If the remote restart_lsn and catalog_xmin have caught up with the
553 : * local ones, then update the LSNs and persist the local synced slot for
554 : * future synchronization; otherwise, do nothing.
555 : *
556 : * Return true if the slot is marked as RS_PERSISTENT (sync-ready), otherwise
557 : * false.
558 : */
559 : static bool
560 10 : update_and_persist_local_synced_slot(RemoteSlot *remote_slot, Oid remote_dbid)
561 : {
562 10 : ReplicationSlot *slot = MyReplicationSlot;
563 10 : bool found_consistent_snapshot = false;
564 10 : bool remote_slot_precedes = false;
565 :
566 10 : (void) update_local_synced_slot(remote_slot, remote_dbid,
567 : &found_consistent_snapshot,
568 : &remote_slot_precedes);
569 :
570 : /*
571 : * Check if the primary server has caught up. Refer to the comment atop
572 : * the file for details on this check.
573 : */
574 10 : if (remote_slot_precedes)
575 : {
576 : /*
577 : * The remote slot didn't catch up to locally reserved position.
578 : *
579 : * We do not drop the slot because the restart_lsn can be ahead of the
580 : * current location when recreating the slot in the next cycle. It may
581 : * take more time to create such a slot. Therefore, we keep this slot
582 : * and attempt the synchronization in the next cycle.
583 : */
584 0 : return false;
585 : }
586 :
587 : /*
588 : * Don't persist the slot if it cannot reach the consistent point from the
589 : * restart_lsn. See comments atop this file.
590 : */
591 10 : if (!found_consistent_snapshot)
592 : {
593 0 : ereport(LOG,
594 : errmsg("could not synchronize replication slot \"%s\"", remote_slot->name),
595 : errdetail("Synchronization could lead to data loss, because the standby could not build a consistent snapshot to decode WALs at LSN %X/%08X.",
596 : LSN_FORMAT_ARGS(slot->data.restart_lsn)));
597 :
598 0 : return false;
599 : }
600 :
601 10 : ReplicationSlotPersist();
602 :
603 10 : ereport(LOG,
604 : errmsg("newly created replication slot \"%s\" is sync-ready now",
605 : remote_slot->name));
606 :
607 10 : return true;
608 : }
609 :
610 : /*
611 : * Synchronize a single slot to the given position.
612 : *
613 : * This creates a new slot if there is no existing one and updates the
614 : * metadata of the slot as per the data received from the primary server.
615 : *
616 : * The slot is created as a temporary slot and stays in the same state until the
617 : * remote_slot catches up with locally reserved position and local slot is
618 : * updated. The slot is then persisted and is considered as sync-ready for
619 : * periodic syncs.
620 : *
621 : * Returns TRUE if the local slot is updated.
622 : */
623 : static bool
624 78 : synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid)
625 : {
626 : ReplicationSlot *slot;
627 : XLogRecPtr latestFlushPtr;
628 78 : bool slot_updated = false;
629 :
630 : /*
631 : * Make sure that concerned WAL is received and flushed before syncing
632 : * slot to target lsn received from the primary server.
633 : */
634 78 : latestFlushPtr = GetStandbyFlushRecPtr(NULL);
635 78 : if (remote_slot->confirmed_lsn > latestFlushPtr)
636 : {
637 : /*
638 : * Can get here only if GUC 'synchronized_standby_slots' on the
639 : * primary server was not configured correctly.
640 : */
641 0 : ereport(AmLogicalSlotSyncWorkerProcess() ? LOG : ERROR,
642 : errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
643 : errmsg("skipping slot synchronization because the received slot sync"
644 : " LSN %X/%08X for slot \"%s\" is ahead of the standby position %X/%08X",
645 : LSN_FORMAT_ARGS(remote_slot->confirmed_lsn),
646 : remote_slot->name,
647 : LSN_FORMAT_ARGS(latestFlushPtr)));
648 :
649 0 : return false;
650 : }
651 :
652 : /* Search for the named slot */
653 78 : if ((slot = SearchNamedReplicationSlot(remote_slot->name, true)))
654 : {
655 : bool synced;
656 :
657 68 : SpinLockAcquire(&slot->mutex);
658 68 : synced = slot->data.synced;
659 68 : SpinLockRelease(&slot->mutex);
660 :
661 : /* User-created slot with the same name exists, raise ERROR. */
662 68 : if (!synced)
663 0 : ereport(ERROR,
664 : errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
665 : errmsg("exiting from slot synchronization because same"
666 : " name slot \"%s\" already exists on the standby",
667 : remote_slot->name));
668 :
669 : /*
670 : * The slot has been synchronized before.
671 : *
672 : * It is important to acquire the slot here before checking
673 : * invalidation. If we don't acquire the slot first, there could be a
674 : * race condition that the local slot could be invalidated just after
675 : * checking the 'invalidated' flag here and we could end up
676 : * overwriting 'invalidated' flag to remote_slot's value. See
677 : * InvalidatePossiblyObsoleteSlot() where it invalidates slot directly
678 : * if the slot is not acquired by other processes.
679 : *
680 : * XXX: If it ever turns out that slot acquire/release is costly for
681 : * cases when none of the slot properties is changed then we can do a
682 : * pre-check to ensure that at least one of the slot properties is
683 : * changed before acquiring the slot.
684 : */
685 68 : ReplicationSlotAcquire(remote_slot->name, true, false);
686 :
687 : Assert(slot == MyReplicationSlot);
688 :
689 : /*
690 : * Copy the invalidation cause from remote only if local slot is not
691 : * invalidated locally, we don't want to overwrite existing one.
692 : */
693 68 : if (slot->data.invalidated == RS_INVAL_NONE &&
694 68 : remote_slot->invalidated != RS_INVAL_NONE)
695 : {
696 0 : SpinLockAcquire(&slot->mutex);
697 0 : slot->data.invalidated = remote_slot->invalidated;
698 0 : SpinLockRelease(&slot->mutex);
699 :
700 : /* Make sure the invalidated state persists across server restart */
701 0 : ReplicationSlotMarkDirty();
702 0 : ReplicationSlotSave();
703 :
704 0 : slot_updated = true;
705 : }
706 :
707 : /* Skip the sync of an invalidated slot */
708 68 : if (slot->data.invalidated != RS_INVAL_NONE)
709 : {
710 0 : ReplicationSlotRelease();
711 0 : return slot_updated;
712 : }
713 :
714 : /* Slot not ready yet, let's attempt to make it sync-ready now. */
715 68 : if (slot->data.persistency == RS_TEMPORARY)
716 : {
717 0 : slot_updated = update_and_persist_local_synced_slot(remote_slot,
718 : remote_dbid);
719 : }
720 :
721 : /* Slot ready for sync, so sync it. */
722 : else
723 : {
724 : /*
725 : * Sanity check: As long as the invalidations are handled
726 : * appropriately as above, this should never happen.
727 : *
728 : * We don't need to check restart_lsn here. See the comments in
729 : * update_local_synced_slot() for details.
730 : */
731 68 : if (remote_slot->confirmed_lsn < slot->data.confirmed_flush)
732 0 : ereport(ERROR,
733 : errmsg_internal("cannot synchronize local slot \"%s\"",
734 : remote_slot->name),
735 : errdetail_internal("Local slot's start streaming location LSN(%X/%08X) is ahead of remote slot's LSN(%X/%08X).",
736 : LSN_FORMAT_ARGS(slot->data.confirmed_flush),
737 : LSN_FORMAT_ARGS(remote_slot->confirmed_lsn)));
738 :
739 68 : slot_updated = update_local_synced_slot(remote_slot, remote_dbid,
740 : NULL, NULL);
741 : }
742 : }
743 : /* Otherwise create the slot first. */
744 : else
745 : {
746 : NameData plugin_name;
747 10 : TransactionId xmin_horizon = InvalidTransactionId;
748 :
749 : /* Skip creating the local slot if remote_slot is invalidated already */
750 10 : if (remote_slot->invalidated != RS_INVAL_NONE)
751 0 : return false;
752 :
753 : /*
754 : * We create temporary slots instead of ephemeral slots here because
755 : * we want the slots to survive after releasing them. This is done to
756 : * avoid dropping and re-creating the slots in each synchronization
757 : * cycle if the restart_lsn or catalog_xmin of the remote slot has not
758 : * caught up.
759 : */
760 10 : ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
761 10 : remote_slot->two_phase,
762 10 : remote_slot->failover,
763 : true);
764 :
765 : /* For shorter lines. */
766 10 : slot = MyReplicationSlot;
767 :
768 : /* Avoid expensive operations while holding a spinlock. */
769 10 : namestrcpy(&plugin_name, remote_slot->plugin);
770 :
771 10 : SpinLockAcquire(&slot->mutex);
772 10 : slot->data.database = remote_dbid;
773 10 : slot->data.plugin = plugin_name;
774 10 : SpinLockRelease(&slot->mutex);
775 :
776 10 : reserve_wal_for_local_slot(remote_slot->restart_lsn);
777 :
778 10 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
779 10 : xmin_horizon = GetOldestSafeDecodingTransactionId(true);
780 10 : SpinLockAcquire(&slot->mutex);
781 10 : slot->effective_catalog_xmin = xmin_horizon;
782 10 : slot->data.catalog_xmin = xmin_horizon;
783 10 : SpinLockRelease(&slot->mutex);
784 10 : ReplicationSlotsComputeRequiredXmin(true);
785 10 : LWLockRelease(ProcArrayLock);
786 :
787 10 : update_and_persist_local_synced_slot(remote_slot, remote_dbid);
788 :
789 10 : slot_updated = true;
790 : }
791 :
792 78 : ReplicationSlotRelease();
793 :
794 78 : return slot_updated;
795 : }
796 :
797 : /*
798 : * Synchronize slots.
799 : *
800 : * Gets the failover logical slots info from the primary server and updates
801 : * the slots locally. Creates the slots if not present on the standby.
802 : *
803 : * Returns TRUE if any of the slots gets updated in this sync-cycle.
804 : */
805 : static bool
806 42 : synchronize_slots(WalReceiverConn *wrconn)
807 : {
808 : #define SLOTSYNC_COLUMN_COUNT 10
809 42 : Oid slotRow[SLOTSYNC_COLUMN_COUNT] = {TEXTOID, TEXTOID, LSNOID,
810 : LSNOID, XIDOID, BOOLOID, LSNOID, BOOLOID, TEXTOID, TEXTOID};
811 :
812 : WalRcvExecResult *res;
813 : TupleTableSlot *tupslot;
814 42 : List *remote_slot_list = NIL;
815 42 : bool some_slot_updated = false;
816 42 : bool started_tx = false;
817 42 : const char *query = "SELECT slot_name, plugin, confirmed_flush_lsn,"
818 : " restart_lsn, catalog_xmin, two_phase, two_phase_at, failover,"
819 : " database, invalidation_reason"
820 : " FROM pg_catalog.pg_replication_slots"
821 : " WHERE failover and NOT temporary";
822 :
823 : /* The syscache access in walrcv_exec() needs a transaction env. */
824 42 : if (!IsTransactionState())
825 : {
826 28 : StartTransactionCommand();
827 28 : started_tx = true;
828 : }
829 :
830 : /* Execute the query */
831 42 : res = walrcv_exec(wrconn, query, SLOTSYNC_COLUMN_COUNT, slotRow);
832 42 : if (res->status != WALRCV_OK_TUPLES)
833 0 : ereport(ERROR,
834 : errmsg("could not fetch failover logical slots info from the primary server: %s",
835 : res->err));
836 :
837 : /* Construct the remote_slot tuple and synchronize each slot locally */
838 42 : tupslot = MakeSingleTupleTableSlot(res->tupledesc, &TTSOpsMinimalTuple);
839 120 : while (tuplestore_gettupleslot(res->tuplestore, true, false, tupslot))
840 : {
841 : bool isnull;
842 78 : RemoteSlot *remote_slot = palloc0(sizeof(RemoteSlot));
843 : Datum d;
844 78 : int col = 0;
845 :
846 78 : remote_slot->name = TextDatumGetCString(slot_getattr(tupslot, ++col,
847 : &isnull));
848 : Assert(!isnull);
849 :
850 78 : remote_slot->plugin = TextDatumGetCString(slot_getattr(tupslot, ++col,
851 : &isnull));
852 : Assert(!isnull);
853 :
854 : /*
855 : * It is possible to get null values for LSN and Xmin if slot is
856 : * invalidated on the primary server, so handle accordingly.
857 : */
858 78 : d = slot_getattr(tupslot, ++col, &isnull);
859 78 : remote_slot->confirmed_lsn = isnull ? InvalidXLogRecPtr :
860 78 : DatumGetLSN(d);
861 :
862 78 : d = slot_getattr(tupslot, ++col, &isnull);
863 78 : remote_slot->restart_lsn = isnull ? InvalidXLogRecPtr : DatumGetLSN(d);
864 :
865 78 : d = slot_getattr(tupslot, ++col, &isnull);
866 78 : remote_slot->catalog_xmin = isnull ? InvalidTransactionId :
867 78 : DatumGetTransactionId(d);
868 :
869 78 : remote_slot->two_phase = DatumGetBool(slot_getattr(tupslot, ++col,
870 : &isnull));
871 : Assert(!isnull);
872 :
873 78 : d = slot_getattr(tupslot, ++col, &isnull);
874 78 : remote_slot->two_phase_at = isnull ? InvalidXLogRecPtr : DatumGetLSN(d);
875 :
876 78 : remote_slot->failover = DatumGetBool(slot_getattr(tupslot, ++col,
877 : &isnull));
878 : Assert(!isnull);
879 :
880 78 : remote_slot->database = TextDatumGetCString(slot_getattr(tupslot,
881 : ++col, &isnull));
882 : Assert(!isnull);
883 :
884 78 : d = slot_getattr(tupslot, ++col, &isnull);
885 78 : remote_slot->invalidated = isnull ? RS_INVAL_NONE :
886 0 : GetSlotInvalidationCause(TextDatumGetCString(d));
887 :
888 : /* Sanity check */
889 : Assert(col == SLOTSYNC_COLUMN_COUNT);
890 :
891 : /*
892 : * If restart_lsn, confirmed_lsn or catalog_xmin is invalid but the
893 : * slot is valid, that means we have fetched the remote_slot in its
894 : * RS_EPHEMERAL state. In such a case, don't sync it; we can always
895 : * sync it in the next sync cycle when the remote_slot is persisted
896 : * and has valid lsn(s) and xmin values.
897 : *
898 : * XXX: In future, if we plan to expose 'slot->data.persistency' in
899 : * pg_replication_slots view, then we can avoid fetching RS_EPHEMERAL
900 : * slots in the first place.
901 : */
902 78 : if ((XLogRecPtrIsInvalid(remote_slot->restart_lsn) ||
903 78 : XLogRecPtrIsInvalid(remote_slot->confirmed_lsn) ||
904 78 : !TransactionIdIsValid(remote_slot->catalog_xmin)) &&
905 0 : remote_slot->invalidated == RS_INVAL_NONE)
906 0 : pfree(remote_slot);
907 : else
908 : /* Create list of remote slots */
909 78 : remote_slot_list = lappend(remote_slot_list, remote_slot);
910 :
911 78 : ExecClearTuple(tupslot);
912 : }
913 :
914 : /* Drop local slots that no longer need to be synced. */
915 42 : drop_local_obsolete_slots(remote_slot_list);
916 :
917 : /* Now sync the slots locally */
918 162 : foreach_ptr(RemoteSlot, remote_slot, remote_slot_list)
919 : {
920 78 : Oid remote_dbid = get_database_oid(remote_slot->database, false);
921 :
922 : /*
923 : * Use shared lock to prevent a conflict with
924 : * ReplicationSlotsDropDBSlots(), trying to drop the same slot during
925 : * a drop-database operation.
926 : */
927 78 : LockSharedObject(DatabaseRelationId, remote_dbid, 0, AccessShareLock);
928 :
929 78 : some_slot_updated |= synchronize_one_slot(remote_slot, remote_dbid);
930 :
931 78 : UnlockSharedObject(DatabaseRelationId, remote_dbid, 0, AccessShareLock);
932 : }
933 :
934 : /* We are done, free remote_slot_list elements */
935 42 : list_free_deep(remote_slot_list);
936 :
937 42 : walrcv_clear_result(res);
938 :
939 42 : if (started_tx)
940 28 : CommitTransactionCommand();
941 :
942 42 : return some_slot_updated;
943 : }
944 :
945 : /*
946 : * Checks the remote server info.
947 : *
948 : * We ensure that the 'primary_slot_name' exists on the remote server and the
949 : * remote server is not a standby node.
950 : */
951 : static void
952 24 : validate_remote_info(WalReceiverConn *wrconn)
953 : {
954 : #define PRIMARY_INFO_OUTPUT_COL_COUNT 2
955 : WalRcvExecResult *res;
956 24 : Oid slotRow[PRIMARY_INFO_OUTPUT_COL_COUNT] = {BOOLOID, BOOLOID};
957 : StringInfoData cmd;
958 : bool isnull;
959 : TupleTableSlot *tupslot;
960 : bool remote_in_recovery;
961 : bool primary_slot_valid;
962 24 : bool started_tx = false;
963 :
964 24 : initStringInfo(&cmd);
965 24 : appendStringInfo(&cmd,
966 : "SELECT pg_is_in_recovery(), count(*) = 1"
967 : " FROM pg_catalog.pg_replication_slots"
968 : " WHERE slot_type='physical' AND slot_name=%s",
969 : quote_literal_cstr(PrimarySlotName));
970 :
971 : /* The syscache access in walrcv_exec() needs a transaction env. */
972 24 : if (!IsTransactionState())
973 : {
974 8 : StartTransactionCommand();
975 8 : started_tx = true;
976 : }
977 :
978 24 : res = walrcv_exec(wrconn, cmd.data, PRIMARY_INFO_OUTPUT_COL_COUNT, slotRow);
979 24 : pfree(cmd.data);
980 :
981 24 : if (res->status != WALRCV_OK_TUPLES)
982 0 : ereport(ERROR,
983 : errmsg("could not fetch primary slot name \"%s\" info from the primary server: %s",
984 : PrimarySlotName, res->err),
985 : errhint("Check if \"primary_slot_name\" is configured correctly."));
986 :
987 24 : tupslot = MakeSingleTupleTableSlot(res->tupledesc, &TTSOpsMinimalTuple);
988 24 : if (!tuplestore_gettupleslot(res->tuplestore, true, false, tupslot))
989 0 : elog(ERROR,
990 : "failed to fetch tuple for the primary server slot specified by \"primary_slot_name\"");
991 :
992 24 : remote_in_recovery = DatumGetBool(slot_getattr(tupslot, 1, &isnull));
993 : Assert(!isnull);
994 :
995 : /*
996 : * Slot sync is currently not supported on a cascading standby. This is
997 : * because if we allow it, the primary server needs to wait for all the
998 : * cascading standbys, otherwise, logical subscribers can still be ahead
999 : * of one of the cascading standbys which we plan to promote. Thus, to
1000 : * avoid this additional complexity, we restrict it for the time being.
1001 : */
1002 24 : if (remote_in_recovery)
1003 2 : ereport(ERROR,
1004 : errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
1005 : errmsg("cannot synchronize replication slots from a standby server"));
1006 :
1007 22 : primary_slot_valid = DatumGetBool(slot_getattr(tupslot, 2, &isnull));
1008 : Assert(!isnull);
1009 :
1010 22 : if (!primary_slot_valid)
1011 0 : ereport(ERROR,
1012 : errcode(ERRCODE_INVALID_PARAMETER_VALUE),
1013 : /* translator: second %s is a GUC variable name */
1014 : errmsg("replication slot \"%s\" specified by \"%s\" does not exist on primary server",
1015 : PrimarySlotName, "primary_slot_name"));
1016 :
1017 22 : ExecClearTuple(tupslot);
1018 22 : walrcv_clear_result(res);
1019 :
1020 22 : if (started_tx)
1021 8 : CommitTransactionCommand();
1022 22 : }
1023 :
1024 : /*
1025 : * Checks if dbname is specified in 'primary_conninfo'.
1026 : *
1027 : * Error out if not specified otherwise return it.
1028 : */
1029 : char *
1030 26 : CheckAndGetDbnameFromConninfo(void)
1031 : {
1032 : char *dbname;
1033 :
1034 : /*
1035 : * The slot synchronization needs a database connection for walrcv_exec to
1036 : * work.
1037 : */
1038 26 : dbname = walrcv_get_dbname_from_conninfo(PrimaryConnInfo);
1039 26 : if (dbname == NULL)
1040 2 : ereport(ERROR,
1041 : errcode(ERRCODE_INVALID_PARAMETER_VALUE),
1042 :
1043 : /*
1044 : * translator: first %s is a connection option; second %s is a GUC
1045 : * variable name
1046 : */
1047 : errmsg("replication slot synchronization requires \"%s\" to be specified in \"%s\"",
1048 : "dbname", "primary_conninfo"));
1049 24 : return dbname;
1050 : }
1051 :
1052 : /*
1053 : * Return true if all necessary GUCs for slot synchronization are set
1054 : * appropriately, otherwise, return false.
1055 : */
1056 : bool
1057 30 : ValidateSlotSyncParams(int elevel)
1058 : {
1059 : /*
1060 : * Logical slot sync/creation requires wal_level >= logical.
1061 : */
1062 30 : if (wal_level < WAL_LEVEL_LOGICAL)
1063 : {
1064 0 : ereport(elevel,
1065 : errcode(ERRCODE_INVALID_PARAMETER_VALUE),
1066 : errmsg("replication slot synchronization requires \"wal_level\" >= \"logical\""));
1067 0 : return false;
1068 : }
1069 :
1070 : /*
1071 : * A physical replication slot(primary_slot_name) is required on the
1072 : * primary to ensure that the rows needed by the standby are not removed
1073 : * after restarting, so that the synchronized slot on the standby will not
1074 : * be invalidated.
1075 : */
1076 30 : if (PrimarySlotName == NULL || *PrimarySlotName == '\0')
1077 : {
1078 0 : ereport(elevel,
1079 : errcode(ERRCODE_INVALID_PARAMETER_VALUE),
1080 : /* translator: %s is a GUC variable name */
1081 : errmsg("replication slot synchronization requires \"%s\" to be set", "primary_slot_name"));
1082 0 : return false;
1083 : }
1084 :
1085 : /*
1086 : * hot_standby_feedback must be enabled to cooperate with the physical
1087 : * replication slot, which allows informing the primary about the xmin and
1088 : * catalog_xmin values on the standby.
1089 : */
1090 30 : if (!hot_standby_feedback)
1091 : {
1092 2 : ereport(elevel,
1093 : errcode(ERRCODE_INVALID_PARAMETER_VALUE),
1094 : /* translator: %s is a GUC variable name */
1095 : errmsg("replication slot synchronization requires \"%s\" to be enabled",
1096 : "hot_standby_feedback"));
1097 2 : return false;
1098 : }
1099 :
1100 : /*
1101 : * The primary_conninfo is required to make connection to primary for
1102 : * getting slots information.
1103 : */
1104 28 : if (PrimaryConnInfo == NULL || *PrimaryConnInfo == '\0')
1105 : {
1106 0 : ereport(elevel,
1107 : errcode(ERRCODE_INVALID_PARAMETER_VALUE),
1108 : /* translator: %s is a GUC variable name */
1109 : errmsg("replication slot synchronization requires \"%s\" to be set",
1110 : "primary_conninfo"));
1111 0 : return false;
1112 : }
1113 :
1114 28 : return true;
1115 : }
1116 :
1117 : /*
1118 : * Re-read the config file.
1119 : *
1120 : * Exit if any of the slot sync GUCs have changed. The postmaster will
1121 : * restart it.
1122 : */
1123 : static void
1124 2 : slotsync_reread_config(void)
1125 : {
1126 2 : char *old_primary_conninfo = pstrdup(PrimaryConnInfo);
1127 2 : char *old_primary_slotname = pstrdup(PrimarySlotName);
1128 2 : bool old_sync_replication_slots = sync_replication_slots;
1129 2 : bool old_hot_standby_feedback = hot_standby_feedback;
1130 : bool conninfo_changed;
1131 : bool primary_slotname_changed;
1132 :
1133 : Assert(sync_replication_slots);
1134 :
1135 2 : ConfigReloadPending = false;
1136 2 : ProcessConfigFile(PGC_SIGHUP);
1137 :
1138 2 : conninfo_changed = strcmp(old_primary_conninfo, PrimaryConnInfo) != 0;
1139 2 : primary_slotname_changed = strcmp(old_primary_slotname, PrimarySlotName) != 0;
1140 2 : pfree(old_primary_conninfo);
1141 2 : pfree(old_primary_slotname);
1142 :
1143 2 : if (old_sync_replication_slots != sync_replication_slots)
1144 : {
1145 0 : ereport(LOG,
1146 : /* translator: %s is a GUC variable name */
1147 : errmsg("replication slot synchronization worker will shut down because \"%s\" is disabled", "sync_replication_slots"));
1148 0 : proc_exit(0);
1149 : }
1150 :
1151 2 : if (conninfo_changed ||
1152 2 : primary_slotname_changed ||
1153 2 : (old_hot_standby_feedback != hot_standby_feedback))
1154 : {
1155 2 : ereport(LOG,
1156 : errmsg("replication slot synchronization worker will restart because of a parameter change"));
1157 :
1158 : /*
1159 : * Reset the last-start time for this worker so that the postmaster
1160 : * can restart it without waiting for SLOTSYNC_RESTART_INTERVAL_SEC.
1161 : */
1162 2 : SlotSyncCtx->last_start_time = 0;
1163 :
1164 2 : proc_exit(0);
1165 : }
1166 :
1167 0 : }
1168 :
1169 : /*
1170 : * Interrupt handler for main loop of slot sync worker.
1171 : */
1172 : static void
1173 36 : ProcessSlotSyncInterrupts(void)
1174 : {
1175 36 : CHECK_FOR_INTERRUPTS();
1176 :
1177 32 : if (ShutdownRequestPending)
1178 : {
1179 2 : ereport(LOG,
1180 : errmsg("replication slot synchronization worker is shutting down on receiving SIGINT"));
1181 :
1182 2 : proc_exit(0);
1183 : }
1184 :
1185 30 : if (ConfigReloadPending)
1186 2 : slotsync_reread_config();
1187 28 : }
1188 :
1189 : /*
1190 : * Connection cleanup function for slotsync worker.
1191 : *
1192 : * Called on slotsync worker exit.
1193 : */
1194 : static void
1195 8 : slotsync_worker_disconnect(int code, Datum arg)
1196 : {
1197 8 : WalReceiverConn *wrconn = (WalReceiverConn *) DatumGetPointer(arg);
1198 :
1199 8 : walrcv_disconnect(wrconn);
1200 8 : }
1201 :
1202 : /*
1203 : * Cleanup function for slotsync worker.
1204 : *
1205 : * Called on slotsync worker exit.
1206 : */
1207 : static void
1208 8 : slotsync_worker_onexit(int code, Datum arg)
1209 : {
1210 : /*
1211 : * We need to do slots cleanup here just like WalSndErrorCleanup() does.
1212 : *
1213 : * The startup process during promotion invokes ShutDownSlotSync() which
1214 : * waits for slot sync to finish and it does that by checking the
1215 : * 'syncing' flag. Thus the slot sync worker must be done with slots'
1216 : * release and cleanup to avoid any dangling temporary slots or active
1217 : * slots before it marks itself as finished syncing.
1218 : */
1219 :
1220 : /* Make sure active replication slots are released */
1221 8 : if (MyReplicationSlot != NULL)
1222 0 : ReplicationSlotRelease();
1223 :
1224 : /* Also cleanup the temporary slots. */
1225 8 : ReplicationSlotCleanup(false);
1226 :
1227 8 : SpinLockAcquire(&SlotSyncCtx->mutex);
1228 :
1229 8 : SlotSyncCtx->pid = InvalidPid;
1230 :
1231 : /*
1232 : * If syncing_slots is true, it indicates that the process errored out
1233 : * without resetting the flag. So, we need to clean up shared memory and
1234 : * reset the flag here.
1235 : */
1236 8 : if (syncing_slots)
1237 : {
1238 8 : SlotSyncCtx->syncing = false;
1239 8 : syncing_slots = false;
1240 : }
1241 :
1242 8 : SpinLockRelease(&SlotSyncCtx->mutex);
1243 8 : }
1244 :
1245 : /*
1246 : * Sleep for long enough that we believe it's likely that the slots on primary
1247 : * get updated.
1248 : *
1249 : * If there is no slot activity the wait time between sync-cycles will double
1250 : * (to a maximum of 30s). If there is some slot activity the wait time between
1251 : * sync-cycles is reset to the minimum (200ms).
1252 : */
1253 : static void
1254 28 : wait_for_slot_activity(bool some_slot_updated)
1255 : {
1256 : int rc;
1257 :
1258 28 : if (!some_slot_updated)
1259 : {
1260 : /*
1261 : * No slots were updated, so double the sleep time, but not beyond the
1262 : * maximum allowable value.
1263 : */
1264 16 : sleep_ms = Min(sleep_ms * 2, MAX_SLOTSYNC_WORKER_NAPTIME_MS);
1265 : }
1266 : else
1267 : {
1268 : /*
1269 : * Some slots were updated since the last sleep, so reset the sleep
1270 : * time.
1271 : */
1272 12 : sleep_ms = MIN_SLOTSYNC_WORKER_NAPTIME_MS;
1273 : }
1274 :
1275 28 : rc = WaitLatch(MyLatch,
1276 : WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
1277 : sleep_ms,
1278 : WAIT_EVENT_REPLICATION_SLOTSYNC_MAIN);
1279 :
1280 28 : if (rc & WL_LATCH_SET)
1281 10 : ResetLatch(MyLatch);
1282 28 : }
1283 :
1284 : /*
1285 : * Emit an error if a promotion or a concurrent sync call is in progress.
1286 : * Otherwise, advertise that a sync is in progress.
1287 : */
1288 : static void
1289 24 : check_and_set_sync_info(pid_t worker_pid)
1290 : {
1291 24 : SpinLockAcquire(&SlotSyncCtx->mutex);
1292 :
1293 : /* The worker pid must not be already assigned in SlotSyncCtx */
1294 : Assert(worker_pid == InvalidPid || SlotSyncCtx->pid == InvalidPid);
1295 :
1296 : /*
1297 : * Emit an error if startup process signaled the slot sync machinery to
1298 : * stop. See comments atop SlotSyncCtxStruct.
1299 : */
1300 24 : if (SlotSyncCtx->stopSignaled)
1301 : {
1302 0 : SpinLockRelease(&SlotSyncCtx->mutex);
1303 0 : ereport(ERROR,
1304 : errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
1305 : errmsg("cannot synchronize replication slots when standby promotion is ongoing"));
1306 : }
1307 :
1308 24 : if (SlotSyncCtx->syncing)
1309 : {
1310 0 : SpinLockRelease(&SlotSyncCtx->mutex);
1311 0 : ereport(ERROR,
1312 : errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
1313 : errmsg("cannot synchronize replication slots concurrently"));
1314 : }
1315 :
1316 24 : SlotSyncCtx->syncing = true;
1317 :
1318 : /*
1319 : * Advertise the required PID so that the startup process can kill the
1320 : * slot sync worker on promotion.
1321 : */
1322 24 : SlotSyncCtx->pid = worker_pid;
1323 :
1324 24 : SpinLockRelease(&SlotSyncCtx->mutex);
1325 :
1326 24 : syncing_slots = true;
1327 24 : }
1328 :
1329 : /*
1330 : * Reset syncing flag.
1331 : */
1332 : static void
1333 16 : reset_syncing_flag()
1334 : {
1335 16 : SpinLockAcquire(&SlotSyncCtx->mutex);
1336 16 : SlotSyncCtx->syncing = false;
1337 16 : SpinLockRelease(&SlotSyncCtx->mutex);
1338 :
1339 16 : syncing_slots = false;
1340 16 : };
1341 :
1342 : /*
1343 : * The main loop of our worker process.
1344 : *
1345 : * It connects to the primary server, fetches logical failover slots
1346 : * information periodically in order to create and sync the slots.
1347 : */
1348 : void
1349 8 : ReplSlotSyncWorkerMain(const void *startup_data, size_t startup_data_len)
1350 : {
1351 8 : WalReceiverConn *wrconn = NULL;
1352 : char *dbname;
1353 : char *err;
1354 : sigjmp_buf local_sigjmp_buf;
1355 : StringInfoData app_name;
1356 :
1357 : Assert(startup_data_len == 0);
1358 :
1359 8 : MyBackendType = B_SLOTSYNC_WORKER;
1360 :
1361 8 : init_ps_display(NULL);
1362 :
1363 : Assert(GetProcessingMode() == InitProcessing);
1364 :
1365 : /*
1366 : * Create a per-backend PGPROC struct in shared memory. We must do this
1367 : * before we access any shared memory.
1368 : */
1369 8 : InitProcess();
1370 :
1371 : /*
1372 : * Early initialization.
1373 : */
1374 8 : BaseInit();
1375 :
1376 : Assert(SlotSyncCtx != NULL);
1377 :
1378 : /*
1379 : * If an exception is encountered, processing resumes here.
1380 : *
1381 : * We just need to clean up, report the error, and go away.
1382 : *
1383 : * If we do not have this handling here, then since this worker process
1384 : * operates at the bottom of the exception stack, ERRORs turn into FATALs.
1385 : * Therefore, we create our own exception handler to catch ERRORs.
1386 : */
1387 8 : if (sigsetjmp(local_sigjmp_buf, 1) != 0)
1388 : {
1389 : /* since not using PG_TRY, must reset error stack by hand */
1390 0 : error_context_stack = NULL;
1391 :
1392 : /* Prevents interrupts while cleaning up */
1393 0 : HOLD_INTERRUPTS();
1394 :
1395 : /* Report the error to the server log */
1396 0 : EmitErrorReport();
1397 :
1398 : /*
1399 : * We can now go away. Note that because we called InitProcess, a
1400 : * callback was registered to do ProcKill, which will clean up
1401 : * necessary state.
1402 : */
1403 0 : proc_exit(0);
1404 : }
1405 :
1406 : /* We can now handle ereport(ERROR) */
1407 8 : PG_exception_stack = &local_sigjmp_buf;
1408 :
1409 : /* Setup signal handling */
1410 8 : pqsignal(SIGHUP, SignalHandlerForConfigReload);
1411 8 : pqsignal(SIGINT, SignalHandlerForShutdownRequest);
1412 8 : pqsignal(SIGTERM, die);
1413 8 : pqsignal(SIGFPE, FloatExceptionHandler);
1414 8 : pqsignal(SIGUSR1, procsignal_sigusr1_handler);
1415 8 : pqsignal(SIGUSR2, SIG_IGN);
1416 8 : pqsignal(SIGPIPE, SIG_IGN);
1417 8 : pqsignal(SIGCHLD, SIG_DFL);
1418 :
1419 8 : check_and_set_sync_info(MyProcPid);
1420 :
1421 8 : ereport(LOG, errmsg("slot sync worker started"));
1422 :
1423 : /* Register it as soon as SlotSyncCtx->pid is initialized. */
1424 8 : before_shmem_exit(slotsync_worker_onexit, (Datum) 0);
1425 :
1426 : /*
1427 : * Establishes SIGALRM handler and initialize timeout module. It is needed
1428 : * by InitPostgres to register different timeouts.
1429 : */
1430 8 : InitializeTimeouts();
1431 :
1432 : /* Load the libpq-specific functions */
1433 8 : load_file("libpqwalreceiver", false);
1434 :
1435 : /*
1436 : * Unblock signals (they were blocked when the postmaster forked us)
1437 : */
1438 8 : sigprocmask(SIG_SETMASK, &UnBlockSig, NULL);
1439 :
1440 : /*
1441 : * Set always-secure search path, so malicious users can't redirect user
1442 : * code (e.g. operators).
1443 : *
1444 : * It's not strictly necessary since we won't be scanning or writing to
1445 : * any user table locally, but it's good to retain it here for added
1446 : * precaution.
1447 : */
1448 8 : SetConfigOption("search_path", "", PGC_SUSET, PGC_S_OVERRIDE);
1449 :
1450 8 : dbname = CheckAndGetDbnameFromConninfo();
1451 :
1452 : /*
1453 : * Connect to the database specified by the user in primary_conninfo. We
1454 : * need a database connection for walrcv_exec to work which we use to
1455 : * fetch slot information from the remote node. See comments atop
1456 : * libpqrcv_exec.
1457 : *
1458 : * We do not specify a specific user here since the slot sync worker will
1459 : * operate as a superuser. This is safe because the slot sync worker does
1460 : * not interact with user tables, eliminating the risk of executing
1461 : * arbitrary code within triggers.
1462 : */
1463 8 : InitPostgres(dbname, InvalidOid, NULL, InvalidOid, 0, NULL);
1464 :
1465 8 : SetProcessingMode(NormalProcessing);
1466 :
1467 8 : initStringInfo(&app_name);
1468 8 : if (cluster_name[0])
1469 8 : appendStringInfo(&app_name, "%s_%s", cluster_name, "slotsync worker");
1470 : else
1471 0 : appendStringInfoString(&app_name, "slotsync worker");
1472 :
1473 : /*
1474 : * Establish the connection to the primary server for slot
1475 : * synchronization.
1476 : */
1477 8 : wrconn = walrcv_connect(PrimaryConnInfo, false, false, false,
1478 : app_name.data, &err);
1479 :
1480 8 : if (!wrconn)
1481 0 : ereport(ERROR,
1482 : errcode(ERRCODE_CONNECTION_FAILURE),
1483 : errmsg("synchronization worker \"%s\" could not connect to the primary server: %s",
1484 : app_name.data, err));
1485 :
1486 8 : pfree(app_name.data);
1487 :
1488 : /*
1489 : * Register the disconnection callback.
1490 : *
1491 : * XXX: This can be combined with previous cleanup registration of
1492 : * slotsync_worker_onexit() but that will need the connection to be made
1493 : * global and we want to avoid introducing global for this purpose.
1494 : */
1495 8 : before_shmem_exit(slotsync_worker_disconnect, PointerGetDatum(wrconn));
1496 :
1497 : /*
1498 : * Using the specified primary server connection, check that we are not a
1499 : * cascading standby and slot configured in 'primary_slot_name' exists on
1500 : * the primary server.
1501 : */
1502 8 : validate_remote_info(wrconn);
1503 :
1504 : /* Main loop to synchronize slots */
1505 : for (;;)
1506 28 : {
1507 36 : bool some_slot_updated = false;
1508 :
1509 36 : ProcessSlotSyncInterrupts();
1510 :
1511 28 : some_slot_updated = synchronize_slots(wrconn);
1512 :
1513 28 : wait_for_slot_activity(some_slot_updated);
1514 : }
1515 :
1516 : /*
1517 : * The slot sync worker can't get here because it will only stop when it
1518 : * receives a SIGINT from the startup process, or when there is an error.
1519 : */
1520 : Assert(false);
1521 : }
1522 :
1523 : /*
1524 : * Update the inactive_since property for synced slots.
1525 : *
1526 : * Note that this function is currently called when we shutdown the slot
1527 : * sync machinery.
1528 : */
1529 : static void
1530 1772 : update_synced_slots_inactive_since(void)
1531 : {
1532 1772 : TimestampTz now = 0;
1533 :
1534 : /*
1535 : * We need to update inactive_since only when we are promoting standby to
1536 : * correctly interpret the inactive_since if the standby gets promoted
1537 : * without a restart. We don't want the slots to appear inactive for a
1538 : * long time after promotion if they haven't been synchronized recently.
1539 : * Whoever acquires the slot, i.e., makes the slot active, will reset it.
1540 : */
1541 1772 : if (!StandbyMode)
1542 1680 : return;
1543 :
1544 : /* The slot sync worker or SQL function mustn't be running by now */
1545 : Assert((SlotSyncCtx->pid == InvalidPid) && !SlotSyncCtx->syncing);
1546 :
1547 92 : LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
1548 :
1549 988 : for (int i = 0; i < max_replication_slots; i++)
1550 : {
1551 896 : ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
1552 :
1553 : /* Check if it is a synchronized slot */
1554 896 : if (s->in_use && s->data.synced)
1555 : {
1556 : Assert(SlotIsLogical(s));
1557 :
1558 : /* The slot must not be acquired by any process */
1559 : Assert(s->active_pid == 0);
1560 :
1561 : /* Use the same inactive_since time for all the slots. */
1562 6 : if (now == 0)
1563 4 : now = GetCurrentTimestamp();
1564 :
1565 6 : ReplicationSlotSetInactiveSince(s, now, true);
1566 : }
1567 : }
1568 :
1569 92 : LWLockRelease(ReplicationSlotControlLock);
1570 : }
1571 :
1572 : /*
1573 : * Shut down the slot sync worker.
1574 : *
1575 : * This function sends signal to shutdown slot sync worker, if required. It
1576 : * also waits till the slot sync worker has exited or
1577 : * pg_sync_replication_slots() has finished.
1578 : */
1579 : void
1580 1772 : ShutDownSlotSync(void)
1581 : {
1582 : pid_t worker_pid;
1583 :
1584 1772 : SpinLockAcquire(&SlotSyncCtx->mutex);
1585 :
1586 1772 : SlotSyncCtx->stopSignaled = true;
1587 :
1588 : /*
1589 : * Return if neither the slot sync worker is running nor the function
1590 : * pg_sync_replication_slots() is executing.
1591 : */
1592 1772 : if (!SlotSyncCtx->syncing)
1593 : {
1594 1770 : SpinLockRelease(&SlotSyncCtx->mutex);
1595 1770 : update_synced_slots_inactive_since();
1596 1770 : return;
1597 : }
1598 :
1599 2 : worker_pid = SlotSyncCtx->pid;
1600 :
1601 2 : SpinLockRelease(&SlotSyncCtx->mutex);
1602 :
1603 2 : if (worker_pid != InvalidPid)
1604 2 : kill(worker_pid, SIGINT);
1605 :
1606 : /* Wait for slot sync to end */
1607 : for (;;)
1608 0 : {
1609 : int rc;
1610 :
1611 : /* Wait a bit, we don't expect to have to wait long */
1612 2 : rc = WaitLatch(MyLatch,
1613 : WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
1614 : 10L, WAIT_EVENT_REPLICATION_SLOTSYNC_SHUTDOWN);
1615 :
1616 2 : if (rc & WL_LATCH_SET)
1617 : {
1618 0 : ResetLatch(MyLatch);
1619 0 : CHECK_FOR_INTERRUPTS();
1620 : }
1621 :
1622 2 : SpinLockAcquire(&SlotSyncCtx->mutex);
1623 :
1624 : /* Ensure that no process is syncing the slots. */
1625 2 : if (!SlotSyncCtx->syncing)
1626 2 : break;
1627 :
1628 0 : SpinLockRelease(&SlotSyncCtx->mutex);
1629 : }
1630 :
1631 2 : SpinLockRelease(&SlotSyncCtx->mutex);
1632 :
1633 2 : update_synced_slots_inactive_since();
1634 : }
1635 :
1636 : /*
1637 : * SlotSyncWorkerCanRestart
1638 : *
1639 : * Returns true if enough time (SLOTSYNC_RESTART_INTERVAL_SEC) has passed
1640 : * since it was launched last. Otherwise returns false.
1641 : *
1642 : * This is a safety valve to protect against continuous respawn attempts if the
1643 : * worker is dying immediately at launch. Note that since we will retry to
1644 : * launch the worker from the postmaster main loop, we will get another
1645 : * chance later.
1646 : */
1647 : bool
1648 10 : SlotSyncWorkerCanRestart(void)
1649 : {
1650 10 : time_t curtime = time(NULL);
1651 :
1652 : /* Return false if too soon since last start. */
1653 10 : if ((unsigned int) (curtime - SlotSyncCtx->last_start_time) <
1654 : (unsigned int) SLOTSYNC_RESTART_INTERVAL_SEC)
1655 2 : return false;
1656 :
1657 8 : SlotSyncCtx->last_start_time = curtime;
1658 :
1659 8 : return true;
1660 : }
1661 :
1662 : /*
1663 : * Is current process syncing replication slots?
1664 : *
1665 : * Could be either backend executing SQL function or slot sync worker.
1666 : */
1667 : bool
1668 42 : IsSyncingReplicationSlots(void)
1669 : {
1670 42 : return syncing_slots;
1671 : }
1672 :
1673 : /*
1674 : * Amount of shared memory required for slot synchronization.
1675 : */
1676 : Size
1677 6222 : SlotSyncShmemSize(void)
1678 : {
1679 6222 : return sizeof(SlotSyncCtxStruct);
1680 : }
1681 :
1682 : /*
1683 : * Allocate and initialize the shared memory of slot synchronization.
1684 : */
1685 : void
1686 2174 : SlotSyncShmemInit(void)
1687 : {
1688 2174 : Size size = SlotSyncShmemSize();
1689 : bool found;
1690 :
1691 2174 : SlotSyncCtx = (SlotSyncCtxStruct *)
1692 2174 : ShmemInitStruct("Slot Sync Data", size, &found);
1693 :
1694 2174 : if (!found)
1695 : {
1696 2174 : memset(SlotSyncCtx, 0, size);
1697 2174 : SlotSyncCtx->pid = InvalidPid;
1698 2174 : SpinLockInit(&SlotSyncCtx->mutex);
1699 : }
1700 2174 : }
1701 :
1702 : /*
1703 : * Error cleanup callback for slot sync SQL function.
1704 : */
1705 : static void
1706 2 : slotsync_failure_callback(int code, Datum arg)
1707 : {
1708 2 : WalReceiverConn *wrconn = (WalReceiverConn *) DatumGetPointer(arg);
1709 :
1710 : /*
1711 : * We need to do slots cleanup here just like WalSndErrorCleanup() does.
1712 : *
1713 : * The startup process during promotion invokes ShutDownSlotSync() which
1714 : * waits for slot sync to finish and it does that by checking the
1715 : * 'syncing' flag. Thus the SQL function must be done with slots' release
1716 : * and cleanup to avoid any dangling temporary slots or active slots
1717 : * before it marks itself as finished syncing.
1718 : */
1719 :
1720 : /* Make sure active replication slots are released */
1721 2 : if (MyReplicationSlot != NULL)
1722 0 : ReplicationSlotRelease();
1723 :
1724 : /* Also cleanup the synced temporary slots. */
1725 2 : ReplicationSlotCleanup(true);
1726 :
1727 : /*
1728 : * The set syncing_slots indicates that the process errored out without
1729 : * resetting the flag. So, we need to clean up shared memory and reset the
1730 : * flag here.
1731 : */
1732 2 : if (syncing_slots)
1733 2 : reset_syncing_flag();
1734 :
1735 2 : walrcv_disconnect(wrconn);
1736 2 : }
1737 :
1738 : /*
1739 : * Synchronize the failover enabled replication slots using the specified
1740 : * primary server connection.
1741 : */
1742 : void
1743 16 : SyncReplicationSlots(WalReceiverConn *wrconn)
1744 : {
1745 16 : PG_ENSURE_ERROR_CLEANUP(slotsync_failure_callback, PointerGetDatum(wrconn));
1746 : {
1747 16 : check_and_set_sync_info(InvalidPid);
1748 :
1749 16 : validate_remote_info(wrconn);
1750 :
1751 14 : synchronize_slots(wrconn);
1752 :
1753 : /* Cleanup the synced temporary slots */
1754 14 : ReplicationSlotCleanup(true);
1755 :
1756 : /* We are done with sync, so reset sync flag */
1757 14 : reset_syncing_flag();
1758 : }
1759 16 : PG_END_ENSURE_ERROR_CLEANUP(slotsync_failure_callback, PointerGetDatum(wrconn));
1760 14 : }
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