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Don't balance vacuum cost delay when per-table settings are in effect

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When there are cost-delay-related storage options set for a table,
trying to make that table participate in the autovacuum cost-limit
balancing algorithm produces undesirable results: instead of using the
configured values, the global values are always used,
as illustrated by Mark Kirkwood in
http://www.postgresql.org/message-id/52FACF15.8020507@catalyst.net.nz

Since the mechanism is already complicated, just disable it for those
cases rather than trying to make it cope.  There are undesirable
side-effects from this too, namely that the total I/O impact on the
system will be higher whenever such tables are vacuumed.  However, this
is seen as less harmful than slowing down vacuum, because that would
cause bloat to accumulate.  Anyway, in the new system it is possible to
tweak options to get the precise behavior one wants, whereas with the
previous system one was simply hosed.

This has been broken forever, so backpatch to all supported branches.
This might affect systems where cost_limit and cost_delay have been set
for individual tables.
This commit is contained in:
Alvaro Herrera
2014-10-03 13:01:27 -03:00
parent f270a16110
commit 06646f52ea
2 changed files with 26 additions and 6 deletions
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9
doc/src/sgml/maintenance.sgml
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@ -688,10 +688,13 @@ analyze threshold = analyze base threshold + analyze scale factor * number of tu
</para>
<para>
When multiple workers are running, the cost limit is
When multiple workers are running, the cost delay parameters are
<quote>balanced</quote> among all the running workers, so that the
total impact on the system is the same, regardless of the number
of workers actually running.
total I/O impact on the system is the same regardless of the number
of workers actually running. However, any workers processing tables whose
<literal>autovacuum_vacuum_cost_delay</> or
<literal>autovacuum_vacuum_cost_limit</> have been set are not considered
in the balancing algorithm.
</para>
</sect2>
</sect1>