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Add options to control whether VACUUM runs vac_update_datfrozenxid.

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VACUUM normally ends by running vac_update_datfrozenxid(), which
requires a scan of pg_class.  Therefore, if one attempts to vacuum a
database one table at a time --- as vacuumdb has done since v12 ---
we will spend O(N^2) time in vac_update_datfrozenxid().  That causes
serious performance problems in databases with tens of thousands of
tables, and indeed the effect is measurable with only a few hundred.
To add insult to injury, only one process can run
vac_update_datfrozenxid at the same time per DB, so this behavior
largely defeats vacuumdb's -j option.

Hence, invent options SKIP_DATABASE_STATS and ONLY_DATABASE_STATS
to allow applications to postpone vac_update_datfrozenxid() until the
end of a series of VACUUM requests, and teach vacuumdb to use them.

Per bug #17717 from Gunnar L.  Sadly, this answer doesn't seem
like something we'd consider back-patching, so the performance
problem will remain in v12-v15.

Tom Lane and Nathan Bossart

Discussion: https://postgr.es/m/17717-6c50eb1c7d23a886@postgresql.org
This commit is contained in:
Tom Lane
2023-01-06 14:17:25 -05:00
parent cd4b2334db
commit a46a7011b2
10 changed files with 147 additions and 21 deletions
Download Patch File Download Diff File Expand all files Collapse all files

42
src/backend/commands/vacuum.c
View File

@ -114,6 +114,8 @@ ExecVacuum(ParseState *pstate, VacuumStmt *vacstmt, bool isTopLevel)
bool full = false;
bool disable_page_skipping = false;
bool process_toast = true;
bool skip_database_stats = false;
bool only_database_stats = false;
ListCell *lc;
/* index_cleanup and truncate values unspecified for now */
@ -200,6 +202,10 @@ ExecVacuum(ParseState *pstate, VacuumStmt *vacstmt, bool isTopLevel)
params.nworkers = nworkers;
}
}
else if (strcmp(opt->defname, "skip_database_stats") == 0)
skip_database_stats = defGetBoolean(opt);
else if (strcmp(opt->defname, "only_database_stats") == 0)
only_database_stats = defGetBoolean(opt);
else
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
@ -216,7 +222,9 @@ ExecVacuum(ParseState *pstate, VacuumStmt *vacstmt, bool isTopLevel)
(freeze ? VACOPT_FREEZE : 0) |
(full ? VACOPT_FULL : 0) |
(disable_page_skipping ? VACOPT_DISABLE_PAGE_SKIPPING : 0) |
(process_toast ? VACOPT_PROCESS_TOAST : 0);
(process_toast ? VACOPT_PROCESS_TOAST : 0) |
(skip_database_stats ? VACOPT_SKIP_DATABASE_STATS : 0) |
(only_database_stats ? VACOPT_ONLY_DATABASE_STATS : 0);
/* sanity checks on options */
Assert(params.options & (VACOPT_VACUUM | VACOPT_ANALYZE));
@ -349,6 +357,24 @@ vacuum(List *relations, VacuumParams *params,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("PROCESS_TOAST required with VACUUM FULL")));
/* sanity check for ONLY_DATABASE_STATS */
if (params->options & VACOPT_ONLY_DATABASE_STATS)
{
Assert(params->options & VACOPT_VACUUM);
if (relations != NIL)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("ONLY_DATABASE_STATS cannot be specified with a list of tables")));
/* don't require people to turn off PROCESS_TOAST explicitly */
if (params->options & ~(VACOPT_VACUUM |
VACOPT_VERBOSE |
VACOPT_PROCESS_TOAST |
VACOPT_ONLY_DATABASE_STATS))
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("ONLY_DATABASE_STATS cannot be specified with other VACUUM options")));
}
/*
* Create special memory context for cross-transaction storage.
*
@ -376,7 +402,12 @@ vacuum(List *relations, VacuumParams *params,
* Build list of relation(s) to process, putting any new data in
* vac_context for safekeeping.
*/
if (relations != NIL)
if (params->options & VACOPT_ONLY_DATABASE_STATS)
{
/* We don't process any tables in this case */
Assert(relations == NIL);
}
else if (relations != NIL)
{
List *newrels = NIL;
ListCell *lc;
@ -528,11 +559,11 @@ vacuum(List *relations, VacuumParams *params,
StartTransactionCommand();
}
if ((params->options & VACOPT_VACUUM) && !IsAutoVacuumWorkerProcess())
if ((params->options & VACOPT_VACUUM) &&
!(params->options & VACOPT_SKIP_DATABASE_STATS))
{
/*
* Update pg_database.datfrozenxid, and truncate pg_xact if possible.
* (autovacuum.c does this for itself.)
*/
vac_update_datfrozenxid();
}
@ -560,13 +591,14 @@ vacuum_is_permitted_for_relation(Oid relid, Form_pg_class reltuple,
Assert((options & (VACOPT_VACUUM | VACOPT_ANALYZE)) != 0);
/*
/*----------
* A role has privileges to vacuum or analyze the relation if any of the
* following are true:
* - the role is a superuser
* - the role owns the relation
* - the role owns the current database and the relation is not shared
* - the role has been granted the MAINTAIN privilege on the relation
*----------
*/
if (object_ownercheck(RelationRelationId, relid, GetUserId()) ||
(object_ownercheck(DatabaseRelationId, MyDatabaseId, GetUserId()) && !reltuple->relisshared) ||