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Teach autovacuum about multixact member wraparound.

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The logic introduced in commit b69bf30b9b
and repaired in commits 669c7d20e6 and
7be47c56af helps to ensure that we don't
overwrite old multixact member information while it is still needed,
but a user who creates many large multixacts can still exhaust the
member space (and thus start getting errors) while autovacuum stands
idly by.

To fix this, progressively ramp down the effective value (but not the
actual contents) of autovacuum_multixact_freeze_max_age as member space
utilization increases.  This makes autovacuum more aggressive and also
reduces the threshold for a manual VACUUM to perform a full-table scan.

This patch leaves unsolved the problem of ensuring that emergency
autovacuums are triggered even when autovacuum=off.  We'll need to fix
that via a separate patch.

Thomas Munro and Robert Haas
This commit is contained in:
Robert Haas
2015-05-08 12:09:14 -04:00
parent 195fbd4012
commit 53bb309d2d
5 changed files with 130 additions and 11 deletions
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28
src/backend/postmaster/autovacuum.c
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@@ -297,10 +297,12 @@ static void do_autovacuum(void);
static void FreeWorkerInfo(int code, Datum arg);
static autovac_table *table_recheck_autovac(Oid relid, HTAB *table_toast_map,
TupleDesc pg_class_desc);
TupleDesc pg_class_desc,
int effective_multixact_freeze_max_age);
static void relation_needs_vacanalyze(Oid relid, AutoVacOpts *relopts,
Form_pg_class classForm,
PgStat_StatTabEntry *tabentry,
int effective_multixact_freeze_max_age,
bool *dovacuum, bool *doanalyze, bool *wraparound);
static void autovacuum_do_vac_analyze(autovac_table *tab,
@@ -1118,7 +1120,7 @@ do_start_worker(void)
/* Also determine the oldest datminmxid we will consider. */
recentMulti = ReadNextMultiXactId();
multiForceLimit = recentMulti - autovacuum_multixact_freeze_max_age;
multiForceLimit = recentMulti - MultiXactMemberFreezeThreshold();
if (multiForceLimit < FirstMultiXactId)
multiForceLimit -= FirstMultiXactId;
@@ -1881,6 +1883,7 @@ do_autovacuum(void)
BufferAccessStrategy bstrategy;
ScanKeyData key;
TupleDesc pg_class_desc;
int effective_multixact_freeze_max_age;
/*
* StartTransactionCommand and CommitTransactionCommand will automatically
@@ -1910,6 +1913,13 @@ do_autovacuum(void)
*/
pgstat_vacuum_stat();
/*
* Compute the multixact age for which freezing is urgent. This is
* normally autovacuum_multixact_freeze_max_age, but may be less if we
* are short of multixact member space.
*/
effective_multixact_freeze_max_age = MultiXactMemberFreezeThreshold();
/*
* Find the pg_database entry and select the default freeze ages. We use
* zero in template and nonconnectable databases, else the system-wide
@@ -2001,6 +2011,7 @@ do_autovacuum(void)
/* Check if it needs vacuum or analyze */
relation_needs_vacanalyze(relid, relopts, classForm, tabentry,
effective_multixact_freeze_max_age,
&dovacuum, &doanalyze, &wraparound);
/*
@@ -2129,6 +2140,7 @@ do_autovacuum(void)
shared, dbentry);
relation_needs_vacanalyze(relid, relopts, classForm, tabentry,
effective_multixact_freeze_max_age,
&dovacuum, &doanalyze, &wraparound);
/* ignore analyze for toast tables */
@@ -2235,7 +2247,8 @@ do_autovacuum(void)
* the race condition is not closed but it is very small.
*/
MemoryContextSwitchTo(AutovacMemCxt);
tab = table_recheck_autovac(relid, table_toast_map, pg_class_desc);
tab = table_recheck_autovac(relid, table_toast_map, pg_class_desc,
effective_multixact_freeze_max_age);
if (tab == NULL)
{
/* someone else vacuumed the table, or it went away */
@@ -2442,7 +2455,8 @@ get_pgstat_tabentry_relid(Oid relid, bool isshared, PgStat_StatDBEntry *shared,
*/
static autovac_table *
table_recheck_autovac(Oid relid, HTAB *table_toast_map,
TupleDesc pg_class_desc)
TupleDesc pg_class_desc,
int effective_multixact_freeze_max_age)
{
Form_pg_class classForm;
HeapTuple classTup;
@@ -2488,6 +2502,7 @@ table_recheck_autovac(Oid relid, HTAB *table_toast_map,
shared, dbentry);
relation_needs_vacanalyze(relid, avopts, classForm, tabentry,
effective_multixact_freeze_max_age,
&dovacuum, &doanalyze, &wraparound);
/* ignore ANALYZE for toast tables */
@@ -2624,6 +2639,7 @@ relation_needs_vacanalyze(Oid relid,
AutoVacOpts *relopts,
Form_pg_class classForm,
PgStat_StatTabEntry *tabentry,
int effective_multixact_freeze_max_age,
/* output params below */
bool *dovacuum,
bool *doanalyze,
@@ -2684,8 +2700,8 @@ relation_needs_vacanalyze(Oid relid,
: autovacuum_freeze_max_age;
multixact_freeze_max_age = (relopts && relopts->multixact_freeze_max_age >= 0)
? Min(relopts->multixact_freeze_max_age, autovacuum_multixact_freeze_max_age)
: autovacuum_multixact_freeze_max_age;
? Min(relopts->multixact_freeze_max_age, effective_multixact_freeze_max_age)
: effective_multixact_freeze_max_age;
av_enabled = (relopts ? relopts->enabled : true);