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Commitcd142e0

Browse files
author
Amit Kapila
committed
Make pg_replication_origin_drop safe against concurrent drops.
Currently, we get the origin id from the name and then drop the origin bytaking ExclusiveLock on ReplicationOriginRelationId. So, two concurrentsessions can get the id from the name at the same time and then when theytry to drop the origin, one of the sessions will get the either"tuple concurrently deleted" or "cache lookup failed for replicationorigin ..".To prevent this race condition we do the entire operation under lock. Thisobviates the need for replorigin_drop() API and we have removed it so ifany extension authors are using it they need to instead usereplorigin_drop_by_name. See it's usage in pg_replication_origin_drop().Author: Peter SmithReviewed-by: Amit Kapila, Euler Taveira, Petr Jelinek, and AlvaroHerreraDiscussion:https://www.postgresql.org/message-id/CAHut%2BPuW8DWV5fskkMWWMqzt-x7RPcNQOtJQBp6SdwyRghCk7A%40mail.gmail.com
1 parent31c7fb4 commitcd142e0

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3 files changed

+38
-28
lines changed

3 files changed

+38
-28
lines changed

‎src/backend/commands/subscriptioncmds.c

Lines changed: 1 addition & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -926,7 +926,6 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
926926
ListCell*lc;
927927
charoriginname[NAMEDATALEN];
928928
char*err=NULL;
929-
RepOriginIdoriginid;
930929
WalReceiverConn*wrconn=NULL;
931930
StringInfoDatacmd;
932931
Form_pg_subscriptionform;
@@ -1050,9 +1049,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
10501049

10511050
/* Remove the origin tracking if exists. */
10521051
snprintf(originname,sizeof(originname),"pg_%u",subid);
1053-
originid=replorigin_by_name(originname, true);
1054-
if (originid!=InvalidRepOriginId)
1055-
replorigin_drop(originid, false);
1052+
replorigin_drop_by_name(originname, true, false);
10561053

10571054
/*
10581055
* If there is no slot associated with the subscription, we can finish

‎src/backend/replication/logical/origin.c

Lines changed: 36 additions & 23 deletions
Original file line numberDiff line numberDiff line change
@@ -322,27 +322,15 @@ replorigin_create(char *roname)
322322
returnroident;
323323
}
324324

325-
326325
/*
327-
* Drop replication origin.
328-
*
329-
* Needs to be called in a transaction.
326+
* Helper function to drop a replication origin.
330327
*/
331-
void
332-
replorigin_drop(RepOriginIdroident,boolnowait)
328+
staticvoid
329+
replorigin_drop_guts(Relationrel,RepOriginIdroident,boolnowait)
333330
{
334331
HeapTupletuple;
335-
Relationrel;
336332
inti;
337333

338-
Assert(IsTransactionState());
339-
340-
/*
341-
* To interlock against concurrent drops, we hold ExclusiveLock on
342-
* pg_replication_origin throughout this function.
343-
*/
344-
rel=table_open(ReplicationOriginRelationId,ExclusiveLock);
345-
346334
/*
347335
* First, clean up the slot state info, if there is any matching slot.
348336
*/
@@ -415,11 +403,40 @@ replorigin_drop(RepOriginId roident, bool nowait)
415403
ReleaseSysCache(tuple);
416404

417405
CommandCounterIncrement();
418-
419-
/* now release lock again */
420-
table_close(rel,ExclusiveLock);
421406
}
422407

408+
/*
409+
* Drop replication origin (by name).
410+
*
411+
* Needs to be called in a transaction.
412+
*/
413+
void
414+
replorigin_drop_by_name(char*name,boolmissing_ok,boolnowait)
415+
{
416+
RepOriginIdroident;
417+
Relationrel;
418+
419+
Assert(IsTransactionState());
420+
421+
/*
422+
* To interlock against concurrent drops, we hold ExclusiveLock on
423+
* pg_replication_origin till xact commit.
424+
*
425+
* XXX We can optimize this by acquiring the lock on a specific origin by
426+
* using LockSharedObject if required. However, for that, we first to
427+
* acquire a lock on ReplicationOriginRelationId, get the origin_id, lock
428+
* the specific origin and then re-check if the origin still exists.
429+
*/
430+
rel=table_open(ReplicationOriginRelationId,ExclusiveLock);
431+
432+
roident=replorigin_by_name(name,missing_ok);
433+
434+
if (OidIsValid(roident))
435+
replorigin_drop_guts(rel,roident,nowait);
436+
437+
/* We keep the lock on pg_replication_origin until commit */
438+
table_close(rel,NoLock);
439+
}
423440

424441
/*
425442
* Lookup replication origin via its oid and return the name.
@@ -1256,16 +1273,12 @@ Datum
12561273
pg_replication_origin_drop(PG_FUNCTION_ARGS)
12571274
{
12581275
char*name;
1259-
RepOriginIdroident;
12601276

12611277
replorigin_check_prerequisites(false, false);
12621278

12631279
name=text_to_cstring((text*)DatumGetPointer(PG_GETARG_DATUM(0)));
12641280

1265-
roident=replorigin_by_name(name, false);
1266-
Assert(OidIsValid(roident));
1267-
1268-
replorigin_drop(roident, true);
1281+
replorigin_drop_by_name(name, false, true);
12691282

12701283
pfree(name);
12711284

‎src/include/replication/origin.h

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -40,7 +40,7 @@ extern PGDLLIMPORT TimestampTz replorigin_session_origin_timestamp;
4040
/* API for querying & manipulating replication origins */
4141
externRepOriginIdreplorigin_by_name(char*name,boolmissing_ok);
4242
externRepOriginIdreplorigin_create(char*name);
43-
externvoidreplorigin_drop(RepOriginIdroident,boolnowait);
43+
externvoidreplorigin_drop_by_name(char*name,boolmissing_ok,boolnowait);
4444
externboolreplorigin_by_oid(RepOriginIdroident,boolmissing_ok,
4545
char**roname);
4646

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