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Make autovacuum more selective about temp tables to keep

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When temp tables are in danger of XID wraparound, autovacuum drops them;
however, it preserves those that are owned by a working session.  This
is desirable, except when the session is connected to a different
database (because the temp tables cannot be from that session), so make
it only keep the temp tables only if the backend is in the same database
as the temp tables.

This is not bulletproof: it fails to detect temp tables left by a
session whose backend ID is reused in the same database but the new
session does not use temp tables.  Commit 943576bddc fixes that case
too, for branches 11 and up (which is why we don't apply this fix to
those branches), but back-patching that one is not universally agreed
on.

Discussion: https://postgr.es/m/20181214162843.37g6h3txto43akrb@alvherre.pgsql
Reviewed-by: Takayuki Tsunakawa, Michaël Paquier
This commit is contained in:
Alvaro Herrera 2018-12-27 16:00:39 -03:00
parent 285abc8df4
commit 7fc2363a61
1 changed files with 9 additions and 2 deletions
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11
src/backend/postmaster/autovacuum.c
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@ -2046,11 +2046,18 @@ do_autovacuum(void)
if (classForm->relpersistence == RELPERSISTENCE_TEMP)
{
int backendID;
PGPROC *proc;
backendID = GetTempNamespaceBackendId(classForm->relnamespace);
/* We just ignore it if the owning backend is still active */
if (backendID == MyBackendId || BackendIdGetProc(backendID) == NULL)
/*
* We just ignore it if the owning backend is still active in the
* same database.
*/
if (backendID != InvalidBackendId &&
(backendID == MyBackendId ||
(proc = BackendIdGetProc(backendID)) == NULL ||
proc->databaseId != MyDatabaseId))
{
/*
* We found an orphan temp table (which was probably left