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Commitcd312ad

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Prevent inconsistent use of stats entry for replication slots
Concurrent activity around replication slot creation and drop couldcause a replication slot to use a stats entry it should not have usedwhen created, triggering an assertion failure when retrieving aninconsistent entry from the dshash table used by the stats facility.The issue is that pgstat_drop_replslot() calls pgstat_drop_entry()without checking the result. If pgstat_drop_entry() cannot free theentry related to the object dropped, pgstat_request_entry_refs_gc()should be called. AtEOXact_PgStat_DroppedStats() and surroundingroutines dropping stats entries already do that.This is documented in pgstat_internal.h, but let's add a comment at thetop of pgstat_drop_entry() as that can be easy to miss.Reported-by: Alexander LakhinAuthor: Floris Van NeeAnalyzed-by: Andres FreundDiscussion:https://postgr.es/m/17947-b9554521ad963c9c@postgresql.orgBackpatch-through: 15
1 parent8111e80 commitcd312ad

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‎src/backend/utils/activity/pgstat_replslot.c

Lines changed: 3 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -157,8 +157,9 @@ pgstat_drop_replslot(ReplicationSlot *slot)
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{
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Assert(LWLockHeldByMeInMode(ReplicationSlotAllocationLock,LW_EXCLUSIVE));
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pgstat_drop_entry(PGSTAT_KIND_REPLSLOT,InvalidOid,
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ReplicationSlotIndex(slot));
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if (!pgstat_drop_entry(PGSTAT_KIND_REPLSLOT,InvalidOid,
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ReplicationSlotIndex(slot)))
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pgstat_request_entry_refs_gc();
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}
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/*

‎src/backend/utils/activity/pgstat_shmem.c

Lines changed: 11 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -855,6 +855,17 @@ pgstat_drop_database_and_contents(Oid dboid)
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pgstat_request_entry_refs_gc();
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}
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/*
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* Drop a single stats entry.
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*
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* This routine returns false if the stats entry of the dropped object could
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* not be freed, true otherwise.
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*
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* The callers of this function should call pgstat_request_entry_refs_gc()
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* if the stats entry could not be freed, to ensure that this entry's memory
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* can be reclaimed later by a different backend calling
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* pgstat_gc_entry_refs().
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*/
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bool
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pgstat_drop_entry(PgStat_Kindkind,Oiddboid,Oidobjoid)
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{

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