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 "commands/dbcommands.h"
56 : #include "libpq/pqsignal.h"
57 : #include "pgstat.h"
58 : #include "postmaster/interrupt.h"
59 : #include "replication/logical.h"
60 : #include "replication/slotsync.h"
61 : #include "replication/snapbuild.h"
62 : #include "storage/ipc.h"
63 : #include "storage/lmgr.h"
64 : #include "storage/proc.h"
65 : #include "storage/procarray.h"
66 : #include "tcop/tcopprot.h"
67 : #include "utils/builtins.h"
68 : #include "utils/pg_lsn.h"
69 : #include "utils/ps_status.h"
70 : #include "utils/timeout.h"
71 :
72 : /*
73 : * Struct for sharing information to control slot synchronization.
74 : *
75 : * The slot sync worker's pid is needed by the startup process to shut it
76 : * down during promotion. The startup process shuts down the slot sync worker
77 : * and also sets stopSignaled=true to handle the race condition when the
78 : * postmaster has not noticed the promotion yet and thus may end up restarting
79 : * the slot sync worker. If stopSignaled is set, the worker will exit in such a
80 : * case. The SQL function pg_sync_replication_slots() will also error out if
81 : * this flag is set. Note that we don't need to reset this variable as after
82 : * promotion the slot sync worker won't be restarted because the pmState
83 : * changes to PM_RUN from PM_HOT_STANDBY and we don't support demoting
84 : * primary without restarting the server. See LaunchMissingBackgroundProcesses.
85 : *
86 : * The 'syncing' flag is needed to prevent concurrent slot syncs to avoid slot
87 : * overwrites.
88 : *
89 : * The 'last_start_time' is needed by postmaster to start the slot sync worker
90 : * once per SLOTSYNC_RESTART_INTERVAL_SEC. In cases where an immediate restart
91 : * is expected (e.g., slot sync GUCs change), slot sync worker will reset
92 : * last_start_time before exiting, so that postmaster can start the worker
93 : * without waiting for SLOTSYNC_RESTART_INTERVAL_SEC.
94 : */
95 : typedef struct SlotSyncCtxStruct
96 : {
97 : pid_t pid;
98 : bool stopSignaled;
99 : bool syncing;
100 : time_t last_start_time;
101 : slock_t mutex;
102 : } SlotSyncCtxStruct;
103 :
104 : static SlotSyncCtxStruct *SlotSyncCtx = NULL;
105 :
106 : /* GUC variable */
107 : bool sync_replication_slots = false;
108 :
109 : /*
110 : * The sleep time (ms) between slot-sync cycles varies dynamically
111 : * (within a MIN/MAX range) according to slot activity. See
112 : * wait_for_slot_activity() for details.
113 : */
114 : #define MIN_SLOTSYNC_WORKER_NAPTIME_MS 200
115 : #define MAX_SLOTSYNC_WORKER_NAPTIME_MS 30000 /* 30s */
116 :
117 : static long sleep_ms = MIN_SLOTSYNC_WORKER_NAPTIME_MS;
118 :
119 : /* The restart interval for slot sync work used by postmaster */
120 : #define SLOTSYNC_RESTART_INTERVAL_SEC 10
121 :
122 : /*
123 : * Flag to tell if we are syncing replication slots. Unlike the 'syncing' flag
124 : * in SlotSyncCtxStruct, this flag is true only if the current process is
125 : * performing slot synchronization.
126 : */
127 : static bool syncing_slots = false;
128 :
129 : /*
130 : * Structure to hold information fetched from the primary server about a logical
131 : * replication slot.
132 : */
133 : typedef struct RemoteSlot
134 : {
135 : char *name;
136 : char *plugin;
137 : char *database;
138 : bool two_phase;
139 : bool failover;
140 : XLogRecPtr restart_lsn;
141 : XLogRecPtr confirmed_lsn;
142 : XLogRecPtr two_phase_at;
143 : TransactionId catalog_xmin;
144 :
145 : /* RS_INVAL_NONE if valid, or the reason of invalidation */
146 : ReplicationSlotInvalidationCause invalidated;
147 : } RemoteSlot;
148 :
149 : static void slotsync_failure_callback(int code, Datum arg);
150 : static void update_synced_slots_inactive_since(void);
151 :
152 : /*
153 : * If necessary, update the local synced slot's metadata based on the data
154 : * from the remote slot.
155 : *
156 : * If no update was needed (the data of the remote slot is the same as the
157 : * local slot) return false, otherwise true.
158 : *
159 : * *found_consistent_snapshot will be true iff the remote slot's LSN or xmin is
160 : * modified, and decoding from the corresponding LSN's can reach a
161 : * consistent snapshot.
162 : *
163 : * *remote_slot_precedes will be true if the remote slot's LSN or xmin
164 : * precedes locally reserved position.
165 : */
166 : static bool
167 64 : update_local_synced_slot(RemoteSlot *remote_slot, Oid remote_dbid,
168 : bool *found_consistent_snapshot,
169 : bool *remote_slot_precedes)
170 : {
171 64 : ReplicationSlot *slot = MyReplicationSlot;
172 64 : bool updated_xmin_or_lsn = false;
173 64 : bool updated_config = false;
174 :
175 : Assert(slot->data.invalidated == RS_INVAL_NONE);
176 :
177 64 : if (found_consistent_snapshot)
178 10 : *found_consistent_snapshot = false;
179 :
180 64 : if (remote_slot_precedes)
181 10 : *remote_slot_precedes = false;
182 :
183 : /*
184 : * Don't overwrite if we already have a newer catalog_xmin and
185 : * restart_lsn.
186 : */
187 128 : if (remote_slot->restart_lsn < slot->data.restart_lsn ||
188 64 : TransactionIdPrecedes(remote_slot->catalog_xmin,
189 : slot->data.catalog_xmin))
190 : {
191 : /*
192 : * This can happen in following situations:
193 : *
194 : * If the slot is temporary, it means either the initial WAL location
195 : * reserved for the local slot is ahead of the remote slot's
196 : * restart_lsn or the initial xmin_horizon computed for the local slot
197 : * is ahead of the remote slot.
198 : *
199 : * If the slot is persistent, both restart_lsn and catalog_xmin of the
200 : * synced slot could still be ahead of the remote slot. Since we use
201 : * slot advance functionality to keep snapbuild/slot updated, it is
202 : * possible that the restart_lsn and catalog_xmin are advanced to a
203 : * later position than it has on the primary. This can happen when
204 : * slot advancing machinery finds running xacts record after reaching
205 : * the consistent state at a later point than the primary where it
206 : * serializes the snapshot and updates the restart_lsn.
207 : *
208 : * We LOG the message if the slot is temporary as it can help the user
209 : * to understand why the slot is not sync-ready. In the case of a
210 : * persistent slot, it would be a more common case and won't directly
211 : * impact the users, so we used DEBUG1 level to log the message.
212 : */
213 0 : ereport(slot->data.persistency == RS_TEMPORARY ? LOG : DEBUG1,
214 : errmsg("could not synchronize replication slot \"%s\" because remote slot precedes local slot",
215 : remote_slot->name),
216 : errdetail("The remote slot has LSN %X/%X and catalog xmin %u, but the local slot has LSN %X/%X and catalog xmin %u.",
217 : LSN_FORMAT_ARGS(remote_slot->restart_lsn),
218 : remote_slot->catalog_xmin,
219 : LSN_FORMAT_ARGS(slot->data.restart_lsn),
220 : slot->data.catalog_xmin));
221 :
222 0 : if (remote_slot_precedes)
223 0 : *remote_slot_precedes = true;
224 :
225 : /*
226 : * Skip updating the configuration. This is required to avoid syncing
227 : * two_phase_at without syncing confirmed_lsn. Otherwise, the prepared
228 : * transaction between old confirmed_lsn and two_phase_at will
229 : * unexpectedly get decoded and sent to the downstream after
230 : * promotion. See comments in ReorderBufferFinishPrepared.
231 : */
232 0 : return false;
233 : }
234 :
235 : /*
236 : * Attempt to sync LSNs and xmins only if remote slot is ahead of local
237 : * slot.
238 : */
239 64 : if (remote_slot->confirmed_lsn > slot->data.confirmed_flush ||
240 86 : remote_slot->restart_lsn > slot->data.restart_lsn ||
241 42 : TransactionIdFollows(remote_slot->catalog_xmin,
242 : slot->data.catalog_xmin))
243 : {
244 : /*
245 : * We can't directly copy the remote slot's LSN or xmin unless there
246 : * exists a consistent snapshot at that point. Otherwise, after
247 : * promotion, the slots may not reach a consistent point before the
248 : * confirmed_flush_lsn which can lead to a data loss. To avoid data
249 : * loss, we let slot machinery advance the slot which ensures that
250 : * snapbuilder/slot statuses are updated properly.
251 : */
252 22 : if (SnapBuildSnapshotExists(remote_slot->restart_lsn))
253 : {
254 : /*
255 : * Update the slot info directly if there is a serialized snapshot
256 : * at the restart_lsn, as the slot can quickly reach consistency
257 : * at restart_lsn by restoring the snapshot.
258 : */
259 4 : SpinLockAcquire(&slot->mutex);
260 4 : slot->data.restart_lsn = remote_slot->restart_lsn;
261 4 : slot->data.confirmed_flush = remote_slot->confirmed_lsn;
262 4 : slot->data.catalog_xmin = remote_slot->catalog_xmin;
263 4 : SpinLockRelease(&slot->mutex);
264 :
265 4 : if (found_consistent_snapshot)
266 0 : *found_consistent_snapshot = true;
267 : }
268 : else
269 : {
270 18 : LogicalSlotAdvanceAndCheckSnapState(remote_slot->confirmed_lsn,
271 : found_consistent_snapshot);
272 :
273 : /* Sanity check */
274 18 : if (slot->data.confirmed_flush != remote_slot->confirmed_lsn)
275 0 : ereport(ERROR,
276 : errmsg_internal("synchronized confirmed_flush for slot \"%s\" differs from remote slot",
277 : remote_slot->name),
278 : errdetail_internal("Remote slot has LSN %X/%X but local slot has LSN %X/%X.",
279 : LSN_FORMAT_ARGS(remote_slot->confirmed_lsn),
280 : LSN_FORMAT_ARGS(slot->data.confirmed_flush)));
281 : }
282 :
283 22 : updated_xmin_or_lsn = true;
284 : }
285 :
286 64 : if (remote_dbid != slot->data.database ||
287 64 : remote_slot->two_phase != slot->data.two_phase ||
288 62 : remote_slot->failover != slot->data.failover ||
289 62 : strcmp(remote_slot->plugin, NameStr(slot->data.plugin)) != 0 ||
290 62 : remote_slot->two_phase_at != slot->data.two_phase_at)
291 : {
292 : NameData plugin_name;
293 :
294 : /* Avoid expensive operations while holding a spinlock. */
295 2 : namestrcpy(&plugin_name, remote_slot->plugin);
296 :
297 2 : SpinLockAcquire(&slot->mutex);
298 2 : slot->data.plugin = plugin_name;
299 2 : slot->data.database = remote_dbid;
300 2 : slot->data.two_phase = remote_slot->two_phase;
301 2 : slot->data.two_phase_at = remote_slot->two_phase_at;
302 2 : slot->data.failover = remote_slot->failover;
303 2 : SpinLockRelease(&slot->mutex);
304 :
305 2 : updated_config = true;
306 :
307 : /*
308 : * Ensure that there is no risk of sending prepared transactions
309 : * unexpectedly after the promotion.
310 : */
311 : Assert(slot->data.two_phase_at <= slot->data.confirmed_flush);
312 : }
313 :
314 : /*
315 : * We have to write the changed xmin to disk *before* we change the
316 : * in-memory value, otherwise after a crash we wouldn't know that some
317 : * catalog tuples might have been removed already.
318 : */
319 64 : if (updated_config || updated_xmin_or_lsn)
320 : {
321 22 : ReplicationSlotMarkDirty();
322 22 : ReplicationSlotSave();
323 : }
324 :
325 : /*
326 : * Now the new xmin is safely on disk, we can let the global value
327 : * advance. We do not take ProcArrayLock or similar since we only advance
328 : * xmin here and there's not much harm done by a concurrent computation
329 : * missing that.
330 : */
331 64 : if (updated_xmin_or_lsn)
332 : {
333 22 : SpinLockAcquire(&slot->mutex);
334 22 : slot->effective_catalog_xmin = remote_slot->catalog_xmin;
335 22 : SpinLockRelease(&slot->mutex);
336 :
337 22 : ReplicationSlotsComputeRequiredXmin(false);
338 22 : ReplicationSlotsComputeRequiredLSN();
339 : }
340 :
341 64 : return updated_config || updated_xmin_or_lsn;
342 : }
343 :
344 : /*
345 : * Get the list of local logical slots that are synchronized from the
346 : * primary server.
347 : */
348 : static List *
349 36 : get_local_synced_slots(void)
350 : {
351 36 : List *local_slots = NIL;
352 :
353 36 : LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
354 :
355 396 : for (int i = 0; i < max_replication_slots; i++)
356 : {
357 360 : ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
358 :
359 : /* Check if it is a synchronized slot */
360 360 : if (s->in_use && s->data.synced)
361 : {
362 : Assert(SlotIsLogical(s));
363 60 : local_slots = lappend(local_slots, s);
364 : }
365 : }
366 :
367 36 : LWLockRelease(ReplicationSlotControlLock);
368 :
369 36 : return local_slots;
370 : }
371 :
372 : /*
373 : * Helper function to check if local_slot is required to be retained.
374 : *
375 : * Return false either if local_slot does not exist in the remote_slots list
376 : * or is invalidated while the corresponding remote slot is still valid,
377 : * otherwise true.
378 : */
379 : static bool
380 60 : local_sync_slot_required(ReplicationSlot *local_slot, List *remote_slots)
381 : {
382 60 : bool remote_exists = false;
383 60 : bool locally_invalidated = false;
384 :
385 148 : foreach_ptr(RemoteSlot, remote_slot, remote_slots)
386 : {
387 86 : if (strcmp(remote_slot->name, NameStr(local_slot->data.name)) == 0)
388 : {
389 58 : remote_exists = true;
390 :
391 : /*
392 : * If remote slot is not invalidated but local slot is marked as
393 : * invalidated, then set locally_invalidated flag.
394 : */
395 58 : SpinLockAcquire(&local_slot->mutex);
396 58 : locally_invalidated =
397 116 : (remote_slot->invalidated == RS_INVAL_NONE) &&
398 58 : (local_slot->data.invalidated != RS_INVAL_NONE);
399 58 : SpinLockRelease(&local_slot->mutex);
400 :
401 58 : break;
402 : }
403 : }
404 :
405 60 : return (remote_exists && !locally_invalidated);
406 : }
407 :
408 : /*
409 : * Drop local obsolete slots.
410 : *
411 : * Drop the local slots that no longer need to be synced i.e. these either do
412 : * not exist on the primary or are no longer enabled for failover.
413 : *
414 : * Additionally, drop any slots that are valid on the primary but got
415 : * invalidated on the standby. This situation may occur due to the following
416 : * reasons:
417 : * - The 'max_slot_wal_keep_size' on the standby is insufficient to retain WAL
418 : * records from the restart_lsn of the slot.
419 : * - 'primary_slot_name' is temporarily reset to null and the physical slot is
420 : * removed.
421 : * These dropped slots will get recreated in next sync-cycle and it is okay to
422 : * drop and recreate such slots as long as these are not consumable on the
423 : * standby (which is the case currently).
424 : *
425 : * Note: Change of 'wal_level' on the primary server to a level lower than
426 : * logical may also result in slot invalidation and removal on the standby.
427 : * This is because such 'wal_level' change is only possible if the logical
428 : * slots are removed on the primary server, so it's expected to see the
429 : * slots being invalidated and removed on the standby too (and re-created
430 : * if they are re-created on the primary server).
431 : */
432 : static void
433 36 : drop_local_obsolete_slots(List *remote_slot_list)
434 : {
435 36 : List *local_slots = get_local_synced_slots();
436 :
437 132 : foreach_ptr(ReplicationSlot, local_slot, local_slots)
438 : {
439 : /* Drop the local slot if it is not required to be retained. */
440 60 : if (!local_sync_slot_required(local_slot, remote_slot_list))
441 : {
442 : bool synced_slot;
443 :
444 : /*
445 : * Use shared lock to prevent a conflict with
446 : * ReplicationSlotsDropDBSlots(), trying to drop the same slot
447 : * during a drop-database operation.
448 : */
449 4 : LockSharedObject(DatabaseRelationId, local_slot->data.database,
450 : 0, AccessShareLock);
451 :
452 : /*
453 : * In the small window between getting the slot to drop and
454 : * locking the database, there is a possibility of a parallel
455 : * database drop by the startup process and the creation of a new
456 : * slot by the user. This new user-created slot may end up using
457 : * the same shared memory as that of 'local_slot'. Thus check if
458 : * local_slot is still the synced one before performing actual
459 : * drop.
460 : */
461 4 : SpinLockAcquire(&local_slot->mutex);
462 4 : synced_slot = local_slot->in_use && local_slot->data.synced;
463 4 : SpinLockRelease(&local_slot->mutex);
464 :
465 4 : if (synced_slot)
466 : {
467 4 : ReplicationSlotAcquire(NameStr(local_slot->data.name), true, false);
468 4 : ReplicationSlotDropAcquired();
469 : }
470 :
471 4 : UnlockSharedObject(DatabaseRelationId, local_slot->data.database,
472 : 0, AccessShareLock);
473 :
474 4 : ereport(LOG,
475 : errmsg("dropped replication slot \"%s\" of database with OID %u",
476 : NameStr(local_slot->data.name),
477 : local_slot->data.database));
478 : }
479 : }
480 36 : }
481 :
482 : /*
483 : * Reserve WAL for the currently active local slot using the specified WAL
484 : * location (restart_lsn).
485 : *
486 : * If the given WAL location has been removed, reserve WAL using the oldest
487 : * existing WAL segment.
488 : */
489 : static void
490 10 : reserve_wal_for_local_slot(XLogRecPtr restart_lsn)
491 : {
492 : XLogSegNo oldest_segno;
493 : XLogSegNo segno;
494 10 : ReplicationSlot *slot = MyReplicationSlot;
495 :
496 : Assert(slot != NULL);
497 : Assert(XLogRecPtrIsInvalid(slot->data.restart_lsn));
498 :
499 : while (true)
500 : {
501 10 : SpinLockAcquire(&slot->mutex);
502 10 : slot->data.restart_lsn = restart_lsn;
503 10 : SpinLockRelease(&slot->mutex);
504 :
505 : /* Prevent WAL removal as fast as possible */
506 10 : ReplicationSlotsComputeRequiredLSN();
507 :
508 10 : XLByteToSeg(slot->data.restart_lsn, segno, wal_segment_size);
509 :
510 : /*
511 : * Find the oldest existing WAL segment file.
512 : *
513 : * Normally, we can determine it by using the last removed segment
514 : * number. However, if no WAL segment files have been removed by a
515 : * checkpoint since startup, we need to search for the oldest segment
516 : * file from the current timeline existing in XLOGDIR.
517 : *
518 : * XXX: Currently, we are searching for the oldest segment in the
519 : * current timeline as there is less chance of the slot's restart_lsn
520 : * from being some prior timeline, and even if it happens, in the
521 : * worst case, we will wait to sync till the slot's restart_lsn moved
522 : * to the current timeline.
523 : */
524 10 : oldest_segno = XLogGetLastRemovedSegno() + 1;
525 :
526 10 : if (oldest_segno == 1)
527 : {
528 : TimeLineID cur_timeline;
529 :
530 6 : GetWalRcvFlushRecPtr(NULL, &cur_timeline);
531 6 : oldest_segno = XLogGetOldestSegno(cur_timeline);
532 : }
533 :
534 10 : elog(DEBUG1, "segno: " UINT64_FORMAT " of purposed restart_lsn for the synced slot, oldest_segno: " UINT64_FORMAT " available",
535 : segno, oldest_segno);
536 :
537 : /*
538 : * If all required WAL is still there, great, otherwise retry. The
539 : * slot should prevent further removal of WAL, unless there's a
540 : * concurrent ReplicationSlotsComputeRequiredLSN() after we've written
541 : * the new restart_lsn above, so normally we should never need to loop
542 : * more than twice.
543 : */
544 10 : if (segno >= oldest_segno)
545 10 : break;
546 :
547 : /* Retry using the location of the oldest wal segment */
548 0 : XLogSegNoOffsetToRecPtr(oldest_segno, 0, wal_segment_size, restart_lsn);
549 : }
550 10 : }
551 :
552 : /*
553 : * If the remote restart_lsn and catalog_xmin have caught up with the
554 : * local ones, then update the LSNs and persist the local synced slot for
555 : * future synchronization; otherwise, do nothing.
556 : *
557 : * Return true if the slot is marked as RS_PERSISTENT (sync-ready), otherwise
558 : * false.
559 : */
560 : static bool
561 10 : update_and_persist_local_synced_slot(RemoteSlot *remote_slot, Oid remote_dbid)
562 : {
563 10 : ReplicationSlot *slot = MyReplicationSlot;
564 10 : bool found_consistent_snapshot = false;
565 10 : bool remote_slot_precedes = false;
566 :
567 10 : (void) update_local_synced_slot(remote_slot, remote_dbid,
568 : &found_consistent_snapshot,
569 : &remote_slot_precedes);
570 :
571 : /*
572 : * Check if the primary server has caught up. Refer to the comment atop
573 : * the file for details on this check.
574 : */
575 10 : if (remote_slot_precedes)
576 : {
577 : /*
578 : * The remote slot didn't catch up to locally reserved position.
579 : *
580 : * We do not drop the slot because the restart_lsn can be ahead of the
581 : * current location when recreating the slot in the next cycle. It may
582 : * take more time to create such a slot. Therefore, we keep this slot
583 : * and attempt the synchronization in the next cycle.
584 : */
585 0 : return false;
586 : }
587 :
588 : /*
589 : * Don't persist the slot if it cannot reach the consistent point from the
590 : * restart_lsn. See comments atop this file.
591 : */
592 10 : if (!found_consistent_snapshot)
593 : {
594 0 : ereport(LOG,
595 : errmsg("could not synchronize replication slot \"%s\"", remote_slot->name),
596 : errdetail("Logical decoding could not find consistent point from local slot's LSN %X/%X.",
597 : LSN_FORMAT_ARGS(slot->data.restart_lsn)));
598 :
599 0 : return false;
600 : }
601 :
602 10 : ReplicationSlotPersist();
603 :
604 10 : ereport(LOG,
605 : errmsg("newly created replication slot \"%s\" is sync-ready now",
606 : remote_slot->name));
607 :
608 10 : return true;
609 : }
610 :
611 : /*
612 : * Synchronize a single slot to the given position.
613 : *
614 : * This creates a new slot if there is no existing one and updates the
615 : * metadata of the slot as per the data received from the primary server.
616 : *
617 : * The slot is created as a temporary slot and stays in the same state until the
618 : * remote_slot catches up with locally reserved position and local slot is
619 : * updated. The slot is then persisted and is considered as sync-ready for
620 : * periodic syncs.
621 : *
622 : * Returns TRUE if the local slot is updated.
623 : */
624 : static bool
625 66 : synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid)
626 : {
627 : ReplicationSlot *slot;
628 : XLogRecPtr latestFlushPtr;
629 66 : bool slot_updated = false;
630 :
631 : /*
632 : * Make sure that concerned WAL is received and flushed before syncing
633 : * slot to target lsn received from the primary server.
634 : */
635 66 : latestFlushPtr = GetStandbyFlushRecPtr(NULL);
636 66 : if (remote_slot->confirmed_lsn > latestFlushPtr)
637 : {
638 : /*
639 : * Can get here only if GUC 'synchronized_standby_slots' on the
640 : * primary server was not configured correctly.
641 : */
642 2 : ereport(AmLogicalSlotSyncWorkerProcess() ? LOG : ERROR,
643 : errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
644 : errmsg("skipping slot synchronization because the received slot sync"
645 : " LSN %X/%X for slot \"%s\" is ahead of the standby position %X/%X",
646 : LSN_FORMAT_ARGS(remote_slot->confirmed_lsn),
647 : remote_slot->name,
648 : LSN_FORMAT_ARGS(latestFlushPtr)));
649 :
650 2 : return false;
651 : }
652 :
653 : /* Search for the named slot */
654 64 : if ((slot = SearchNamedReplicationSlot(remote_slot->name, true)))
655 : {
656 : bool synced;
657 :
658 54 : SpinLockAcquire(&slot->mutex);
659 54 : synced = slot->data.synced;
660 54 : SpinLockRelease(&slot->mutex);
661 :
662 : /* User-created slot with the same name exists, raise ERROR. */
663 54 : if (!synced)
664 0 : ereport(ERROR,
665 : errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
666 : errmsg("exiting from slot synchronization because same"
667 : " name slot \"%s\" already exists on the standby",
668 : remote_slot->name));
669 :
670 : /*
671 : * The slot has been synchronized before.
672 : *
673 : * It is important to acquire the slot here before checking
674 : * invalidation. If we don't acquire the slot first, there could be a
675 : * race condition that the local slot could be invalidated just after
676 : * checking the 'invalidated' flag here and we could end up
677 : * overwriting 'invalidated' flag to remote_slot's value. See
678 : * InvalidatePossiblyObsoleteSlot() where it invalidates slot directly
679 : * if the slot is not acquired by other processes.
680 : *
681 : * XXX: If it ever turns out that slot acquire/release is costly for
682 : * cases when none of the slot properties is changed then we can do a
683 : * pre-check to ensure that at least one of the slot properties is
684 : * changed before acquiring the slot.
685 : */
686 54 : ReplicationSlotAcquire(remote_slot->name, true, false);
687 :
688 : Assert(slot == MyReplicationSlot);
689 :
690 : /*
691 : * Copy the invalidation cause from remote only if local slot is not
692 : * invalidated locally, we don't want to overwrite existing one.
693 : */
694 54 : if (slot->data.invalidated == RS_INVAL_NONE &&
695 54 : remote_slot->invalidated != RS_INVAL_NONE)
696 : {
697 0 : SpinLockAcquire(&slot->mutex);
698 0 : slot->data.invalidated = remote_slot->invalidated;
699 0 : SpinLockRelease(&slot->mutex);
700 :
701 : /* Make sure the invalidated state persists across server restart */
702 0 : ReplicationSlotMarkDirty();
703 0 : ReplicationSlotSave();
704 :
705 0 : slot_updated = true;
706 : }
707 :
708 : /* Skip the sync of an invalidated slot */
709 54 : if (slot->data.invalidated != RS_INVAL_NONE)
710 : {
711 0 : ReplicationSlotRelease();
712 0 : return slot_updated;
713 : }
714 :
715 : /* Slot not ready yet, let's attempt to make it sync-ready now. */
716 54 : if (slot->data.persistency == RS_TEMPORARY)
717 : {
718 0 : slot_updated = update_and_persist_local_synced_slot(remote_slot,
719 : remote_dbid);
720 : }
721 :
722 : /* Slot ready for sync, so sync it. */
723 : else
724 : {
725 : /*
726 : * Sanity check: As long as the invalidations are handled
727 : * appropriately as above, this should never happen.
728 : *
729 : * We don't need to check restart_lsn here. See the comments in
730 : * update_local_synced_slot() for details.
731 : */
732 54 : if (remote_slot->confirmed_lsn < slot->data.confirmed_flush)
733 0 : ereport(ERROR,
734 : errmsg_internal("cannot synchronize local slot \"%s\"",
735 : remote_slot->name),
736 : errdetail_internal("Local slot's start streaming location LSN(%X/%X) is ahead of remote slot's LSN(%X/%X).",
737 : LSN_FORMAT_ARGS(slot->data.confirmed_flush),
738 : LSN_FORMAT_ARGS(remote_slot->confirmed_lsn)));
739 :
740 54 : slot_updated = update_local_synced_slot(remote_slot, remote_dbid,
741 : NULL, NULL);
742 : }
743 : }
744 : /* Otherwise create the slot first. */
745 : else
746 : {
747 : NameData plugin_name;
748 10 : TransactionId xmin_horizon = InvalidTransactionId;
749 :
750 : /* Skip creating the local slot if remote_slot is invalidated already */
751 10 : if (remote_slot->invalidated != RS_INVAL_NONE)
752 0 : return false;
753 :
754 : /*
755 : * We create temporary slots instead of ephemeral slots here because
756 : * we want the slots to survive after releasing them. This is done to
757 : * avoid dropping and re-creating the slots in each synchronization
758 : * cycle if the restart_lsn or catalog_xmin of the remote slot has not
759 : * caught up.
760 : */
761 10 : ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
762 10 : remote_slot->two_phase,
763 10 : remote_slot->failover,
764 : true);
765 :
766 : /* For shorter lines. */
767 10 : slot = MyReplicationSlot;
768 :
769 : /* Avoid expensive operations while holding a spinlock. */
770 10 : namestrcpy(&plugin_name, remote_slot->plugin);
771 :
772 10 : SpinLockAcquire(&slot->mutex);
773 10 : slot->data.database = remote_dbid;
774 10 : slot->data.plugin = plugin_name;
775 10 : SpinLockRelease(&slot->mutex);
776 :
777 10 : reserve_wal_for_local_slot(remote_slot->restart_lsn);
778 :
779 10 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
780 10 : xmin_horizon = GetOldestSafeDecodingTransactionId(true);
781 10 : SpinLockAcquire(&slot->mutex);
782 10 : slot->effective_catalog_xmin = xmin_horizon;
783 10 : slot->data.catalog_xmin = xmin_horizon;
784 10 : SpinLockRelease(&slot->mutex);
785 10 : ReplicationSlotsComputeRequiredXmin(true);
786 10 : LWLockRelease(ProcArrayLock);
787 :
788 10 : update_and_persist_local_synced_slot(remote_slot, remote_dbid);
789 :
790 10 : slot_updated = true;
791 : }
792 :
793 64 : ReplicationSlotRelease();
794 :
795 64 : return slot_updated;
796 : }
797 :
798 : /*
799 : * Synchronize slots.
800 : *
801 : * Gets the failover logical slots info from the primary server and updates
802 : * the slots locally. Creates the slots if not present on the standby.
803 : *
804 : * Returns TRUE if any of the slots gets updated in this sync-cycle.
805 : */
806 : static bool
807 36 : synchronize_slots(WalReceiverConn *wrconn)
808 : {
809 : #define SLOTSYNC_COLUMN_COUNT 10
810 36 : Oid slotRow[SLOTSYNC_COLUMN_COUNT] = {TEXTOID, TEXTOID, LSNOID,
811 : LSNOID, XIDOID, BOOLOID, LSNOID, BOOLOID, TEXTOID, TEXTOID};
812 :
813 : WalRcvExecResult *res;
814 : TupleTableSlot *tupslot;
815 36 : List *remote_slot_list = NIL;
816 36 : bool some_slot_updated = false;
817 36 : bool started_tx = false;
818 36 : const char *query = "SELECT slot_name, plugin, confirmed_flush_lsn,"
819 : " restart_lsn, catalog_xmin, two_phase, two_phase_at, failover,"
820 : " database, invalidation_reason"
821 : " FROM pg_catalog.pg_replication_slots"
822 : " WHERE failover and NOT temporary";
823 :
824 : /* The syscache access in walrcv_exec() needs a transaction env. */
825 36 : if (!IsTransactionState())
826 : {
827 22 : StartTransactionCommand();
828 22 : started_tx = true;
829 : }
830 :
831 : /* Execute the query */
832 36 : res = walrcv_exec(wrconn, query, SLOTSYNC_COLUMN_COUNT, slotRow);
833 36 : if (res->status != WALRCV_OK_TUPLES)
834 0 : ereport(ERROR,
835 : errmsg("could not fetch failover logical slots info from the primary server: %s",
836 : res->err));
837 :
838 : /* Construct the remote_slot tuple and synchronize each slot locally */
839 36 : tupslot = MakeSingleTupleTableSlot(res->tupledesc, &TTSOpsMinimalTuple);
840 102 : while (tuplestore_gettupleslot(res->tuplestore, true, false, tupslot))
841 : {
842 : bool isnull;
843 66 : RemoteSlot *remote_slot = palloc0(sizeof(RemoteSlot));
844 : Datum d;
845 66 : int col = 0;
846 :
847 66 : remote_slot->name = TextDatumGetCString(slot_getattr(tupslot, ++col,
848 : &isnull));
849 : Assert(!isnull);
850 :
851 66 : remote_slot->plugin = TextDatumGetCString(slot_getattr(tupslot, ++col,
852 : &isnull));
853 : Assert(!isnull);
854 :
855 : /*
856 : * It is possible to get null values for LSN and Xmin if slot is
857 : * invalidated on the primary server, so handle accordingly.
858 : */
859 66 : d = slot_getattr(tupslot, ++col, &isnull);
860 66 : remote_slot->confirmed_lsn = isnull ? InvalidXLogRecPtr :
861 66 : DatumGetLSN(d);
862 :
863 66 : d = slot_getattr(tupslot, ++col, &isnull);
864 66 : remote_slot->restart_lsn = isnull ? InvalidXLogRecPtr : DatumGetLSN(d);
865 :
866 66 : d = slot_getattr(tupslot, ++col, &isnull);
867 66 : remote_slot->catalog_xmin = isnull ? InvalidTransactionId :
868 66 : DatumGetTransactionId(d);
869 :
870 66 : remote_slot->two_phase = DatumGetBool(slot_getattr(tupslot, ++col,
871 : &isnull));
872 : Assert(!isnull);
873 :
874 66 : d = slot_getattr(tupslot, ++col, &isnull);
875 66 : remote_slot->two_phase_at = isnull ? InvalidXLogRecPtr : DatumGetLSN(d);
876 :
877 66 : remote_slot->failover = DatumGetBool(slot_getattr(tupslot, ++col,
878 : &isnull));
879 : Assert(!isnull);
880 :
881 66 : remote_slot->database = TextDatumGetCString(slot_getattr(tupslot,
882 : ++col, &isnull));
883 : Assert(!isnull);
884 :
885 66 : d = slot_getattr(tupslot, ++col, &isnull);
886 66 : remote_slot->invalidated = isnull ? RS_INVAL_NONE :
887 0 : GetSlotInvalidationCause(TextDatumGetCString(d));
888 :
889 : /* Sanity check */
890 : Assert(col == SLOTSYNC_COLUMN_COUNT);
891 :
892 : /*
893 : * If restart_lsn, confirmed_lsn or catalog_xmin is invalid but the
894 : * slot is valid, that means we have fetched the remote_slot in its
895 : * RS_EPHEMERAL state. In such a case, don't sync it; we can always
896 : * sync it in the next sync cycle when the remote_slot is persisted
897 : * and has valid lsn(s) and xmin values.
898 : *
899 : * XXX: In future, if we plan to expose 'slot->data.persistency' in
900 : * pg_replication_slots view, then we can avoid fetching RS_EPHEMERAL
901 : * slots in the first place.
902 : */
903 66 : if ((XLogRecPtrIsInvalid(remote_slot->restart_lsn) ||
904 66 : XLogRecPtrIsInvalid(remote_slot->confirmed_lsn) ||
905 66 : !TransactionIdIsValid(remote_slot->catalog_xmin)) &&
906 0 : remote_slot->invalidated == RS_INVAL_NONE)
907 0 : pfree(remote_slot);
908 : else
909 : /* Create list of remote slots */
910 66 : remote_slot_list = lappend(remote_slot_list, remote_slot);
911 :
912 66 : ExecClearTuple(tupslot);
913 : }
914 :
915 : /* Drop local slots that no longer need to be synced. */
916 36 : drop_local_obsolete_slots(remote_slot_list);
917 :
918 : /* Now sync the slots locally */
919 138 : foreach_ptr(RemoteSlot, remote_slot, remote_slot_list)
920 : {
921 66 : Oid remote_dbid = get_database_oid(remote_slot->database, false);
922 :
923 : /*
924 : * Use shared lock to prevent a conflict with
925 : * ReplicationSlotsDropDBSlots(), trying to drop the same slot during
926 : * a drop-database operation.
927 : */
928 66 : LockSharedObject(DatabaseRelationId, remote_dbid, 0, AccessShareLock);
929 :
930 66 : some_slot_updated |= synchronize_one_slot(remote_slot, remote_dbid);
931 :
932 66 : UnlockSharedObject(DatabaseRelationId, remote_dbid, 0, AccessShareLock);
933 : }
934 :
935 : /* We are done, free remote_slot_list elements */
936 36 : list_free_deep(remote_slot_list);
937 :
938 36 : walrcv_clear_result(res);
939 :
940 36 : if (started_tx)
941 22 : CommitTransactionCommand();
942 :
943 36 : return some_slot_updated;
944 : }
945 :
946 : /*
947 : * Checks the remote server info.
948 : *
949 : * We ensure that the 'primary_slot_name' exists on the remote server and the
950 : * remote server is not a standby node.
951 : */
952 : static void
953 24 : validate_remote_info(WalReceiverConn *wrconn)
954 : {
955 : #define PRIMARY_INFO_OUTPUT_COL_COUNT 2
956 : WalRcvExecResult *res;
957 24 : Oid slotRow[PRIMARY_INFO_OUTPUT_COL_COUNT] = {BOOLOID, BOOLOID};
958 : StringInfoData cmd;
959 : bool isnull;
960 : TupleTableSlot *tupslot;
961 : bool remote_in_recovery;
962 : bool primary_slot_valid;
963 24 : bool started_tx = false;
964 :
965 24 : initStringInfo(&cmd);
966 24 : appendStringInfo(&cmd,
967 : "SELECT pg_is_in_recovery(), count(*) = 1"
968 : " FROM pg_catalog.pg_replication_slots"
969 : " WHERE slot_type='physical' AND slot_name=%s",
970 : quote_literal_cstr(PrimarySlotName));
971 :
972 : /* The syscache access in walrcv_exec() needs a transaction env. */
973 24 : if (!IsTransactionState())
974 : {
975 8 : StartTransactionCommand();
976 8 : started_tx = true;
977 : }
978 :
979 24 : res = walrcv_exec(wrconn, cmd.data, PRIMARY_INFO_OUTPUT_COL_COUNT, slotRow);
980 24 : pfree(cmd.data);
981 :
982 24 : if (res->status != WALRCV_OK_TUPLES)
983 0 : ereport(ERROR,
984 : errmsg("could not fetch primary slot name \"%s\" info from the primary server: %s",
985 : PrimarySlotName, res->err),
986 : errhint("Check if \"primary_slot_name\" is configured correctly."));
987 :
988 24 : tupslot = MakeSingleTupleTableSlot(res->tupledesc, &TTSOpsMinimalTuple);
989 24 : if (!tuplestore_gettupleslot(res->tuplestore, true, false, tupslot))
990 0 : elog(ERROR,
991 : "failed to fetch tuple for the primary server slot specified by \"primary_slot_name\"");
992 :
993 24 : remote_in_recovery = DatumGetBool(slot_getattr(tupslot, 1, &isnull));
994 : Assert(!isnull);
995 :
996 : /*
997 : * Slot sync is currently not supported on a cascading standby. This is
998 : * because if we allow it, the primary server needs to wait for all the
999 : * cascading standbys, otherwise, logical subscribers can still be ahead
1000 : * of one of the cascading standbys which we plan to promote. Thus, to
1001 : * avoid this additional complexity, we restrict it for the time being.
1002 : */
1003 24 : if (remote_in_recovery)
1004 2 : ereport(ERROR,
1005 : errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
1006 : errmsg("cannot synchronize replication slots from a standby server"));
1007 :
1008 22 : primary_slot_valid = DatumGetBool(slot_getattr(tupslot, 2, &isnull));
1009 : Assert(!isnull);
1010 :
1011 22 : if (!primary_slot_valid)
1012 0 : ereport(ERROR,
1013 : errcode(ERRCODE_INVALID_PARAMETER_VALUE),
1014 : /* translator: second %s is a GUC variable name */
1015 : errmsg("replication slot \"%s\" specified by \"%s\" does not exist on primary server",
1016 : PrimarySlotName, "primary_slot_name"));
1017 :
1018 22 : ExecClearTuple(tupslot);
1019 22 : walrcv_clear_result(res);
1020 :
1021 22 : if (started_tx)
1022 8 : CommitTransactionCommand();
1023 22 : }
1024 :
1025 : /*
1026 : * Checks if dbname is specified in 'primary_conninfo'.
1027 : *
1028 : * Error out if not specified otherwise return it.
1029 : */
1030 : char *
1031 26 : CheckAndGetDbnameFromConninfo(void)
1032 : {
1033 : char *dbname;
1034 :
1035 : /*
1036 : * The slot synchronization needs a database connection for walrcv_exec to
1037 : * work.
1038 : */
1039 26 : dbname = walrcv_get_dbname_from_conninfo(PrimaryConnInfo);
1040 26 : if (dbname == NULL)
1041 2 : ereport(ERROR,
1042 : errcode(ERRCODE_INVALID_PARAMETER_VALUE),
1043 :
1044 : /*
1045 : * translator: first %s is a connection option; second %s is a GUC
1046 : * variable name
1047 : */
1048 : errmsg("replication slot synchronization requires \"%s\" to be specified in \"%s\"",
1049 : "dbname", "primary_conninfo"));
1050 24 : return dbname;
1051 : }
1052 :
1053 : /*
1054 : * Return true if all necessary GUCs for slot synchronization are set
1055 : * appropriately, otherwise, return false.
1056 : */
1057 : bool
1058 30 : ValidateSlotSyncParams(int elevel)
1059 : {
1060 : /*
1061 : * Logical slot sync/creation requires wal_level >= logical.
1062 : *
1063 : * Since altering the wal_level requires a server restart, so error out in
1064 : * this case regardless of elevel provided by caller.
1065 : */
1066 30 : if (wal_level < WAL_LEVEL_LOGICAL)
1067 0 : ereport(ERROR,
1068 : errcode(ERRCODE_INVALID_PARAMETER_VALUE),
1069 : errmsg("replication slot synchronization requires \"wal_level\" >= \"logical\""));
1070 :
1071 : /*
1072 : * A physical replication slot(primary_slot_name) is required on the
1073 : * primary to ensure that the rows needed by the standby are not removed
1074 : * after restarting, so that the synchronized slot on the standby will not
1075 : * be invalidated.
1076 : */
1077 30 : if (PrimarySlotName == NULL || *PrimarySlotName == '\0')
1078 : {
1079 0 : ereport(elevel,
1080 : errcode(ERRCODE_INVALID_PARAMETER_VALUE),
1081 : /* translator: %s is a GUC variable name */
1082 : errmsg("replication slot synchronization requires \"%s\" to be set", "primary_slot_name"));
1083 0 : return false;
1084 : }
1085 :
1086 : /*
1087 : * hot_standby_feedback must be enabled to cooperate with the physical
1088 : * replication slot, which allows informing the primary about the xmin and
1089 : * catalog_xmin values on the standby.
1090 : */
1091 30 : if (!hot_standby_feedback)
1092 : {
1093 2 : ereport(elevel,
1094 : errcode(ERRCODE_INVALID_PARAMETER_VALUE),
1095 : /* translator: %s is a GUC variable name */
1096 : errmsg("replication slot synchronization requires \"%s\" to be enabled",
1097 : "hot_standby_feedback"));
1098 2 : return false;
1099 : }
1100 :
1101 : /*
1102 : * The primary_conninfo is required to make connection to primary for
1103 : * getting slots information.
1104 : */
1105 28 : if (PrimaryConnInfo == NULL || *PrimaryConnInfo == '\0')
1106 : {
1107 0 : ereport(elevel,
1108 : errcode(ERRCODE_INVALID_PARAMETER_VALUE),
1109 : /* translator: %s is a GUC variable name */
1110 : errmsg("replication slot synchronization requires \"%s\" to be set",
1111 : "primary_conninfo"));
1112 0 : return false;
1113 : }
1114 :
1115 28 : return true;
1116 : }
1117 :
1118 : /*
1119 : * Re-read the config file.
1120 : *
1121 : * Exit if any of the slot sync GUCs have changed. The postmaster will
1122 : * restart it.
1123 : */
1124 : static void
1125 2 : slotsync_reread_config(void)
1126 : {
1127 2 : char *old_primary_conninfo = pstrdup(PrimaryConnInfo);
1128 2 : char *old_primary_slotname = pstrdup(PrimarySlotName);
1129 2 : bool old_sync_replication_slots = sync_replication_slots;
1130 2 : bool old_hot_standby_feedback = hot_standby_feedback;
1131 : bool conninfo_changed;
1132 : bool primary_slotname_changed;
1133 :
1134 : Assert(sync_replication_slots);
1135 :
1136 2 : ConfigReloadPending = false;
1137 2 : ProcessConfigFile(PGC_SIGHUP);
1138 :
1139 2 : conninfo_changed = strcmp(old_primary_conninfo, PrimaryConnInfo) != 0;
1140 2 : primary_slotname_changed = strcmp(old_primary_slotname, PrimarySlotName) != 0;
1141 2 : pfree(old_primary_conninfo);
1142 2 : pfree(old_primary_slotname);
1143 :
1144 2 : if (old_sync_replication_slots != sync_replication_slots)
1145 : {
1146 0 : ereport(LOG,
1147 : /* translator: %s is a GUC variable name */
1148 : errmsg("replication slot synchronization worker will shut down because \"%s\" is disabled", "sync_replication_slots"));
1149 0 : proc_exit(0);
1150 : }
1151 :
1152 2 : if (conninfo_changed ||
1153 2 : primary_slotname_changed ||
1154 2 : (old_hot_standby_feedback != hot_standby_feedback))
1155 : {
1156 2 : ereport(LOG,
1157 : errmsg("replication slot synchronization worker will restart because of a parameter change"));
1158 :
1159 : /*
1160 : * Reset the last-start time for this worker so that the postmaster
1161 : * can restart it without waiting for SLOTSYNC_RESTART_INTERVAL_SEC.
1162 : */
1163 2 : SlotSyncCtx->last_start_time = 0;
1164 :
1165 2 : proc_exit(0);
1166 : }
1167 :
1168 0 : }
1169 :
1170 : /*
1171 : * Interrupt handler for main loop of slot sync worker.
1172 : */
1173 : static void
1174 30 : ProcessSlotSyncInterrupts(WalReceiverConn *wrconn)
1175 : {
1176 30 : CHECK_FOR_INTERRUPTS();
1177 :
1178 26 : if (ShutdownRequestPending)
1179 : {
1180 2 : ereport(LOG,
1181 : errmsg("replication slot synchronization worker is shutting down on receiving SIGINT"));
1182 :
1183 2 : proc_exit(0);
1184 : }
1185 :
1186 24 : if (ConfigReloadPending)
1187 2 : slotsync_reread_config();
1188 22 : }
1189 :
1190 : /*
1191 : * Connection cleanup function for slotsync worker.
1192 : *
1193 : * Called on slotsync worker exit.
1194 : */
1195 : static void
1196 8 : slotsync_worker_disconnect(int code, Datum arg)
1197 : {
1198 8 : WalReceiverConn *wrconn = (WalReceiverConn *) DatumGetPointer(arg);
1199 :
1200 8 : walrcv_disconnect(wrconn);
1201 8 : }
1202 :
1203 : /*
1204 : * Cleanup function for slotsync worker.
1205 : *
1206 : * Called on slotsync worker exit.
1207 : */
1208 : static void
1209 8 : slotsync_worker_onexit(int code, Datum arg)
1210 : {
1211 : /*
1212 : * We need to do slots cleanup here just like WalSndErrorCleanup() does.
1213 : *
1214 : * The startup process during promotion invokes ShutDownSlotSync() which
1215 : * waits for slot sync to finish and it does that by checking the
1216 : * 'syncing' flag. Thus the slot sync worker must be done with slots'
1217 : * release and cleanup to avoid any dangling temporary slots or active
1218 : * slots before it marks itself as finished syncing.
1219 : */
1220 :
1221 : /* Make sure active replication slots are released */
1222 8 : if (MyReplicationSlot != NULL)
1223 0 : ReplicationSlotRelease();
1224 :
1225 : /* Also cleanup the temporary slots. */
1226 8 : ReplicationSlotCleanup(false);
1227 :
1228 8 : SpinLockAcquire(&SlotSyncCtx->mutex);
1229 :
1230 8 : SlotSyncCtx->pid = InvalidPid;
1231 :
1232 : /*
1233 : * If syncing_slots is true, it indicates that the process errored out
1234 : * without resetting the flag. So, we need to clean up shared memory and
1235 : * reset the flag here.
1236 : */
1237 8 : if (syncing_slots)
1238 : {
1239 8 : SlotSyncCtx->syncing = false;
1240 8 : syncing_slots = false;
1241 : }
1242 :
1243 8 : SpinLockRelease(&SlotSyncCtx->mutex);
1244 8 : }
1245 :
1246 : /*
1247 : * Sleep for long enough that we believe it's likely that the slots on primary
1248 : * get updated.
1249 : *
1250 : * If there is no slot activity the wait time between sync-cycles will double
1251 : * (to a maximum of 30s). If there is some slot activity the wait time between
1252 : * sync-cycles is reset to the minimum (200ms).
1253 : */
1254 : static void
1255 22 : wait_for_slot_activity(bool some_slot_updated)
1256 : {
1257 : int rc;
1258 :
1259 22 : if (!some_slot_updated)
1260 : {
1261 : /*
1262 : * No slots were updated, so double the sleep time, but not beyond the
1263 : * maximum allowable value.
1264 : */
1265 12 : sleep_ms = Min(sleep_ms * 2, MAX_SLOTSYNC_WORKER_NAPTIME_MS);
1266 : }
1267 : else
1268 : {
1269 : /*
1270 : * Some slots were updated since the last sleep, so reset the sleep
1271 : * time.
1272 : */
1273 10 : sleep_ms = MIN_SLOTSYNC_WORKER_NAPTIME_MS;
1274 : }
1275 :
1276 22 : rc = WaitLatch(MyLatch,
1277 : WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
1278 : sleep_ms,
1279 : WAIT_EVENT_REPLICATION_SLOTSYNC_MAIN);
1280 :
1281 22 : if (rc & WL_LATCH_SET)
1282 8 : ResetLatch(MyLatch);
1283 22 : }
1284 :
1285 : /*
1286 : * Emit an error if a promotion or a concurrent sync call is in progress.
1287 : * Otherwise, advertise that a sync is in progress.
1288 : */
1289 : static void
1290 24 : check_and_set_sync_info(pid_t worker_pid)
1291 : {
1292 24 : SpinLockAcquire(&SlotSyncCtx->mutex);
1293 :
1294 : /* The worker pid must not be already assigned in SlotSyncCtx */
1295 : Assert(worker_pid == InvalidPid || SlotSyncCtx->pid == InvalidPid);
1296 :
1297 : /*
1298 : * Emit an error if startup process signaled the slot sync machinery to
1299 : * stop. See comments atop SlotSyncCtxStruct.
1300 : */
1301 24 : if (SlotSyncCtx->stopSignaled)
1302 : {
1303 0 : SpinLockRelease(&SlotSyncCtx->mutex);
1304 0 : ereport(ERROR,
1305 : errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
1306 : errmsg("cannot synchronize replication slots when standby promotion is ongoing"));
1307 : }
1308 :
1309 24 : if (SlotSyncCtx->syncing)
1310 : {
1311 0 : SpinLockRelease(&SlotSyncCtx->mutex);
1312 0 : ereport(ERROR,
1313 : errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
1314 : errmsg("cannot synchronize replication slots concurrently"));
1315 : }
1316 :
1317 24 : SlotSyncCtx->syncing = true;
1318 :
1319 : /*
1320 : * Advertise the required PID so that the startup process can kill the
1321 : * slot sync worker on promotion.
1322 : */
1323 24 : SlotSyncCtx->pid = worker_pid;
1324 :
1325 24 : SpinLockRelease(&SlotSyncCtx->mutex);
1326 :
1327 24 : syncing_slots = true;
1328 24 : }
1329 :
1330 : /*
1331 : * Reset syncing flag.
1332 : */
1333 : static void
1334 16 : reset_syncing_flag()
1335 : {
1336 16 : SpinLockAcquire(&SlotSyncCtx->mutex);
1337 16 : SlotSyncCtx->syncing = false;
1338 16 : SpinLockRelease(&SlotSyncCtx->mutex);
1339 :
1340 16 : syncing_slots = false;
1341 16 : };
1342 :
1343 : /*
1344 : * The main loop of our worker process.
1345 : *
1346 : * It connects to the primary server, fetches logical failover slots
1347 : * information periodically in order to create and sync the slots.
1348 : */
1349 : void
1350 8 : ReplSlotSyncWorkerMain(const void *startup_data, size_t startup_data_len)
1351 : {
1352 8 : WalReceiverConn *wrconn = NULL;
1353 : char *dbname;
1354 : char *err;
1355 : sigjmp_buf local_sigjmp_buf;
1356 : StringInfoData app_name;
1357 :
1358 : Assert(startup_data_len == 0);
1359 :
1360 8 : MyBackendType = B_SLOTSYNC_WORKER;
1361 :
1362 8 : init_ps_display(NULL);
1363 :
1364 : Assert(GetProcessingMode() == InitProcessing);
1365 :
1366 : /*
1367 : * Create a per-backend PGPROC struct in shared memory. We must do this
1368 : * before we access any shared memory.
1369 : */
1370 8 : InitProcess();
1371 :
1372 : /*
1373 : * Early initialization.
1374 : */
1375 8 : BaseInit();
1376 :
1377 : Assert(SlotSyncCtx != NULL);
1378 :
1379 : /*
1380 : * If an exception is encountered, processing resumes here.
1381 : *
1382 : * We just need to clean up, report the error, and go away.
1383 : *
1384 : * If we do not have this handling here, then since this worker process
1385 : * operates at the bottom of the exception stack, ERRORs turn into FATALs.
1386 : * Therefore, we create our own exception handler to catch ERRORs.
1387 : */
1388 8 : if (sigsetjmp(local_sigjmp_buf, 1) != 0)
1389 : {
1390 : /* since not using PG_TRY, must reset error stack by hand */
1391 0 : error_context_stack = NULL;
1392 :
1393 : /* Prevents interrupts while cleaning up */
1394 0 : HOLD_INTERRUPTS();
1395 :
1396 : /* Report the error to the server log */
1397 0 : EmitErrorReport();
1398 :
1399 : /*
1400 : * We can now go away. Note that because we called InitProcess, a
1401 : * callback was registered to do ProcKill, which will clean up
1402 : * necessary state.
1403 : */
1404 0 : proc_exit(0);
1405 : }
1406 :
1407 : /* We can now handle ereport(ERROR) */
1408 8 : PG_exception_stack = &local_sigjmp_buf;
1409 :
1410 : /* Setup signal handling */
1411 8 : pqsignal(SIGHUP, SignalHandlerForConfigReload);
1412 8 : pqsignal(SIGINT, SignalHandlerForShutdownRequest);
1413 8 : pqsignal(SIGTERM, die);
1414 8 : pqsignal(SIGFPE, FloatExceptionHandler);
1415 8 : pqsignal(SIGUSR1, procsignal_sigusr1_handler);
1416 8 : pqsignal(SIGUSR2, SIG_IGN);
1417 8 : pqsignal(SIGPIPE, SIG_IGN);
1418 8 : pqsignal(SIGCHLD, SIG_DFL);
1419 :
1420 8 : check_and_set_sync_info(MyProcPid);
1421 :
1422 8 : ereport(LOG, errmsg("slot sync worker started"));
1423 :
1424 : /* Register it as soon as SlotSyncCtx->pid is initialized. */
1425 8 : before_shmem_exit(slotsync_worker_onexit, (Datum) 0);
1426 :
1427 : /*
1428 : * Establishes SIGALRM handler and initialize timeout module. It is needed
1429 : * by InitPostgres to register different timeouts.
1430 : */
1431 8 : InitializeTimeouts();
1432 :
1433 : /* Load the libpq-specific functions */
1434 8 : load_file("libpqwalreceiver", false);
1435 :
1436 : /*
1437 : * Unblock signals (they were blocked when the postmaster forked us)
1438 : */
1439 8 : sigprocmask(SIG_SETMASK, &UnBlockSig, NULL);
1440 :
1441 : /*
1442 : * Set always-secure search path, so malicious users can't redirect user
1443 : * code (e.g. operators).
1444 : *
1445 : * It's not strictly necessary since we won't be scanning or writing to
1446 : * any user table locally, but it's good to retain it here for added
1447 : * precaution.
1448 : */
1449 8 : SetConfigOption("search_path", "", PGC_SUSET, PGC_S_OVERRIDE);
1450 :
1451 8 : dbname = CheckAndGetDbnameFromConninfo();
1452 :
1453 : /*
1454 : * Connect to the database specified by the user in primary_conninfo. We
1455 : * need a database connection for walrcv_exec to work which we use to
1456 : * fetch slot information from the remote node. See comments atop
1457 : * libpqrcv_exec.
1458 : *
1459 : * We do not specify a specific user here since the slot sync worker will
1460 : * operate as a superuser. This is safe because the slot sync worker does
1461 : * not interact with user tables, eliminating the risk of executing
1462 : * arbitrary code within triggers.
1463 : */
1464 8 : InitPostgres(dbname, InvalidOid, NULL, InvalidOid, 0, NULL);
1465 :
1466 8 : SetProcessingMode(NormalProcessing);
1467 :
1468 8 : initStringInfo(&app_name);
1469 8 : if (cluster_name[0])
1470 8 : appendStringInfo(&app_name, "%s_%s", cluster_name, "slotsync worker");
1471 : else
1472 0 : appendStringInfoString(&app_name, "slotsync worker");
1473 :
1474 : /*
1475 : * Establish the connection to the primary server for slot
1476 : * synchronization.
1477 : */
1478 8 : wrconn = walrcv_connect(PrimaryConnInfo, false, false, false,
1479 : app_name.data, &err);
1480 8 : pfree(app_name.data);
1481 :
1482 8 : if (!wrconn)
1483 0 : ereport(ERROR,
1484 : errcode(ERRCODE_CONNECTION_FAILURE),
1485 : errmsg("synchronization worker \"%s\" could not connect to the primary server: %s",
1486 : app_name.data, err));
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 22 : {
1507 30 : bool some_slot_updated = false;
1508 :
1509 30 : ProcessSlotSyncInterrupts(wrconn);
1510 :
1511 22 : some_slot_updated = synchronize_slots(wrconn);
1512 :
1513 22 : 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 1698 : update_synced_slots_inactive_since(void)
1531 : {
1532 1698 : 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 1698 : if (!StandbyMode)
1542 1606 : 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 1698 : ShutDownSlotSync(void)
1581 : {
1582 : pid_t worker_pid;
1583 :
1584 1698 : SpinLockAcquire(&SlotSyncCtx->mutex);
1585 :
1586 1698 : 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 1698 : if (!SlotSyncCtx->syncing)
1593 : {
1594 1696 : SpinLockRelease(&SlotSyncCtx->mutex);
1595 1696 : update_synced_slots_inactive_since();
1596 1696 : 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 6006 : SlotSyncShmemSize(void)
1678 : {
1679 6006 : return sizeof(SlotSyncCtxStruct);
1680 : }
1681 :
1682 : /*
1683 : * Allocate and initialize the shared memory of slot synchronization.
1684 : */
1685 : void
1686 2100 : SlotSyncShmemInit(void)
1687 : {
1688 2100 : Size size = SlotSyncShmemSize();
1689 : bool found;
1690 :
1691 2100 : SlotSyncCtx = (SlotSyncCtxStruct *)
1692 2100 : ShmemInitStruct("Slot Sync Data", size, &found);
1693 :
1694 2100 : if (!found)
1695 : {
1696 2100 : memset(SlotSyncCtx, 0, size);
1697 2100 : SlotSyncCtx->pid = InvalidPid;
1698 2100 : SpinLockInit(&SlotSyncCtx->mutex);
1699 : }
1700 2100 : }
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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