diff options
| author | Robert Haas <rhaas@postgresql.org> | 2015-05-08 12:09:14 -0400 |
|---|---|---|
| committer | Robert Haas <rhaas@postgresql.org> | 2015-05-08 12:53:30 -0400 |
| commit | 3ecab37d97ed72bf81fd042dcef10e7111369875 (patch) | |
| tree | 038c31fae28d224d1de4afbe80e6c9ab9cb72eec /doc/src | |
| parent | 32c50af4cf595b609878c160db67bef8ceaaa3c8 (diff) | |
Teach autovacuum about multixact member wraparound.
The logic introduced in commit b69bf30b9bfacafc733a9ba77c9587cf54d06c0c
and repaired in commits 669c7d20e6374850593cb430d332e11a3992bbcf and
7be47c56af3d3013955c91c2877c08f2a0e3e6a2 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
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/maintenance.sgml | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgml index d13a3fbb0ef..01ce9c4c6db 100644 --- a/doc/src/sgml/maintenance.sgml +++ b/doc/src/sgml/maintenance.sgml @@ -628,6 +628,9 @@ HINT: Stop the postmaster and vacuum that database in single-user mode. Like transaction IDs, multixact IDs are implemented as a 32-bit counter and corresponding storage, all of which requires careful aging management, storage cleanup, and wraparound handling. + There is a separate storage area which holds the list of members in + each multixact, which also uses a 32-bit counter and which must also + be managed. </para> <para> @@ -651,7 +654,10 @@ HINT: Stop the postmaster and vacuum that database in single-user mode. As a safety device, a whole-table vacuum scan will occur for any table whose multixact-age is greater than <xref linkend="guc-autovacuum-multixact-freeze-max-age">. - This will occur even if autovacuum is nominally disabled. + This will occur even if autovacuum is nominally disabled. Whole-table + vacuum scans will also occur progressively for all tables, starting with + those that have the oldest multixact-age, if the amount of used member + storage space exceeds the amount 25% of the addressible storage space. </para> </sect3> </sect2> |