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Use heap_inplace_update() to unset pg_database.dathasloginevt 

Doing this instead of regular updates serves two purposes. First, that avoids
possible waiting on the row-level lock.  Second, that avoids dealing with
TOAST.

It's known that changes made by heap_inplace_update() may be lost due to
concurrent normal updates.  However, we are OK with that.  The subsequent
connections will still have a chance to set "dathasloginevt" to false.

Reported-by: Alexander Lakhin
Discussion: https://postgr.es/m/e2a0248e-5f32-af0c-9832-a90d303c2c61%40gmail.com
This commit is contained in:
Alexander Korotkov 2024-02-12 00:33:44 +02:00
parent 428e2de1b8
commit 8be93177c4
1 changed files with 32 additions and 4 deletions
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36
src/backend/commands/event_trigger.c
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@ -13,6 +13,7 @@
*/
#include "postgres.h"
#include "access/heapam.h"
#include "access/htup_details.h"
#include "access/table.h"
#include "access/xact.h"
@ -943,18 +944,45 @@ EventTriggerOnLogin(void)
Relation pg_db = table_open(DatabaseRelationId, RowExclusiveLock);
HeapTuple tuple;
Form_pg_database db;
ScanKeyData key[1];
SysScanDesc scan;
tuple = SearchSysCacheCopy1(DATABASEOID,
ObjectIdGetDatum(MyDatabaseId));
/*
* Get the pg_database tuple to scribble on. Note that this does
* not directly rely on the syscache to avoid issues with
* flattened toast values for the in-place update.
*/
ScanKeyInit(&key[0],
Anum_pg_database_oid,
BTEqualStrategyNumber, F_OIDEQ,
ObjectIdGetDatum(MyDatabaseId));
scan = systable_beginscan(pg_db, DatabaseOidIndexId, true,
NULL, 1, key);
tuple = systable_getnext(scan);
tuple = heap_copytuple(tuple);
systable_endscan(scan);
if (!HeapTupleIsValid(tuple))
elog(ERROR, "cache lookup failed for database %u", MyDatabaseId);
elog(ERROR, "could not find tuple for database %u", MyDatabaseId);
db = (Form_pg_database) GETSTRUCT(tuple);
if (db->dathasloginevt)
{
db->dathasloginevt = false;
CatalogTupleUpdate(pg_db, &tuple->t_self, tuple);
/*
* Do an "in place" update of the pg_database tuple. Doing
* this instead of regular updates serves two purposes. First,
* that avoids possible waiting on the row-level lock. Second,
* that avoids dealing with TOAST.
*
* It's known that changes made by heap_inplace_update() may
* be lost due to concurrent normal updates. However, we are
* OK with that. The subsequent connections will still have a
* chance to set "dathasloginevt" to false.
*/
heap_inplace_update(pg_db, tuple);
}
table_close(pg_db, RowExclusiveLock);
heap_freetuple(tuple);