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Commit8be9317

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committed
Use heap_inplace_update() to unset pg_database.dathasloginevt
Doing this instead of regular updates serves two purposes. First, that avoidspossible waiting on the row-level lock. Second, that avoids dealing withTOAST.It's known that changes made by heap_inplace_update() may be lost due toconcurrent normal updates. However, we are OK with that. The subsequentconnections will still have a chance to set "dathasloginevt" to false.Reported-by: Alexander LakhinDiscussion:https://postgr.es/m/e2a0248e-5f32-af0c-9832-a90d303c2c61%40gmail.com
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‎src/backend/commands/event_trigger.c

Lines changed: 32 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -13,6 +13,7 @@
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*/
1414
#include"postgres.h"
1515

16+
#include"access/heapam.h"
1617
#include"access/htup_details.h"
1718
#include"access/table.h"
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#include"access/xact.h"
@@ -943,18 +944,45 @@ EventTriggerOnLogin(void)
943944
Relationpg_db=table_open(DatabaseRelationId,RowExclusiveLock);
944945
HeapTupletuple;
945946
Form_pg_databasedb;
947+
ScanKeyDatakey[1];
948+
SysScanDescscan;
946949

947-
tuple=SearchSysCacheCopy1(DATABASEOID,
948-
ObjectIdGetDatum(MyDatabaseId));
950+
/*
951+
* Get the pg_database tuple to scribble on. Note that this does
952+
* not directly rely on the syscache to avoid issues with
953+
* flattened toast values for the in-place update.
954+
*/
955+
ScanKeyInit(&key[0],
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Anum_pg_database_oid,
957+
BTEqualStrategyNumber,F_OIDEQ,
958+
ObjectIdGetDatum(MyDatabaseId));
959+
960+
scan=systable_beginscan(pg_db,DatabaseOidIndexId, true,
961+
NULL,1,key);
962+
tuple=systable_getnext(scan);
963+
tuple=heap_copytuple(tuple);
964+
systable_endscan(scan);
949965

950966
if (!HeapTupleIsValid(tuple))
951-
elog(ERROR,"cache lookup failed for database %u",MyDatabaseId);
967+
elog(ERROR,"could not find tuple for database %u",MyDatabaseId);
952968

953969
db= (Form_pg_database)GETSTRUCT(tuple);
954970
if (db->dathasloginevt)
955971
{
956972
db->dathasloginevt= false;
957-
CatalogTupleUpdate(pg_db,&tuple->t_self,tuple);
973+
974+
/*
975+
* Do an "in place" update of the pg_database tuple. Doing
976+
* this instead of regular updates serves two purposes. First,
977+
* that avoids possible waiting on the row-level lock. Second,
978+
* that avoids dealing with TOAST.
979+
*
980+
* It's known that changes made by heap_inplace_update() may
981+
* be lost due to concurrent normal updates. However, we are
982+
* OK with that. The subsequent connections will still have a
983+
* chance to set "dathasloginevt" to false.
984+
*/
985+
heap_inplace_update(pg_db,tuple);
958986
}
959987
table_close(pg_db,RowExclusiveLock);
960988
heap_freetuple(tuple);

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