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Commit4eafdcc

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Prevent logical rep workers with removed subscriptions from starting.
Any logical rep workers must have their subscription entries inpg_subscription. To ensure this, we need to prevent the launcherfrom starting new worker corresponding to the subscription thatDROP SUBSCRIPTION command is removing. To implement this,previously LogicalRepLauncherLock was introduced and held untilthe end of transaction running DROP SUBSCRIPTION. But usingLWLock for that purpose was not valid.Instead, this commit changes DROP SUBSCRIPTION so that it takesAccessExclusiveLock on pg_subscription, in order to ensure thatthe launcher cannot see any subscriptions being removed. Also thiscommit gets rid of LogicalRepLauncherLock.Patch by me, reviewed by Petr JelinekDiscussion:https://www.postgresql.org/message-id/CAHGQGwHPi8ky-yANFfe0sgmhKtsYcQLTnKx07bW9S7-Rn1746w@mail.gmail.com
1 parenta9f66f9 commit4eafdcc

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3 files changed

+7
-18
lines changed

3 files changed

+7
-18
lines changed

‎src/backend/commands/subscriptioncmds.c

Lines changed: 6 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -461,7 +461,12 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
461461
if (stmt->drop_slot)
462462
PreventTransactionChain(isTopLevel,"DROP SUBSCRIPTION ... DROP SLOT");
463463

464-
rel=heap_open(SubscriptionRelationId,RowExclusiveLock);
464+
/*
465+
* Lock pg_subscription with AccessExclusiveLock to ensure
466+
* that the launcher doesn't restart new worker during dropping
467+
* the subscription
468+
*/
469+
rel=heap_open(SubscriptionRelationId,AccessExclusiveLock);
465470

466471
tup=SearchSysCache2(SUBSCRIPTIONNAME,MyDatabaseId,
467472
CStringGetDatum(stmt->subname));
@@ -528,14 +533,9 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
528533
/* Clean up dependencies */
529534
deleteSharedDependencyRecordsFor(SubscriptionRelationId,subid,0);
530535

531-
/* Protect against launcher restarting the worker. */
532-
LWLockAcquire(LogicalRepLauncherLock,LW_EXCLUSIVE);
533-
534536
/* Kill the apply worker so that the slot becomes accessible. */
535537
logicalrep_worker_stop(subid);
536538

537-
LWLockRelease(LogicalRepLauncherLock);
538-
539539
/* Remove the origin tracking if exists. */
540540
snprintf(originname,sizeof(originname),"pg_%u",subid);
541541
originid=replorigin_by_name(originname, true);

‎src/backend/replication/logical/launcher.c

Lines changed: 0 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -305,17 +305,12 @@ logicalrep_worker_launch(Oid dbid, Oid subid, const char *subname, Oid userid)
305305
/*
306306
* Stop the logical replication worker and wait until it detaches from the
307307
* slot.
308-
*
309-
* The caller must hold LogicalRepLauncherLock to ensure that new workers are
310-
* not being started during this function call.
311308
*/
312309
void
313310
logicalrep_worker_stop(Oidsubid)
314311
{
315312
LogicalRepWorker*worker;
316313

317-
Assert(LWLockHeldByMe(LogicalRepLauncherLock));
318-
319314
LWLockAcquire(LogicalRepWorkerLock,LW_SHARED);
320315

321316
worker=logicalrep_worker_find(subid);
@@ -602,9 +597,6 @@ ApplyLauncherMain(Datum main_arg)
602597
ALLOCSET_DEFAULT_MAXSIZE);
603598
oldctx=MemoryContextSwitchTo(subctx);
604599

605-
/* Block any concurrent DROP SUBSCRIPTION. */
606-
LWLockAcquire(LogicalRepLauncherLock,LW_EXCLUSIVE);
607-
608600
/* search for subscriptions to start or stop. */
609601
sublist=get_subscription_list();
610602

@@ -628,8 +620,6 @@ ApplyLauncherMain(Datum main_arg)
628620
}
629621
}
630622

631-
LWLockRelease(LogicalRepLauncherLock);
632-
633623
/* Switch back to original memory context. */
634624
MemoryContextSwitchTo(oldctx);
635625
/* Clean the temporary memory. */

‎src/backend/storage/lmgr/lwlocknames.txt

Lines changed: 1 addition & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -48,5 +48,4 @@ ReplicationOriginLock40
4848
MultiXactTruncationLock41
4949
OldSnapshotTimeMapLock42
5050
BackendRandomLock43
51-
LogicalRepLauncherLock44
52-
LogicalRepWorkerLock45
51+
LogicalRepWorkerLock44

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