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Re: COUNT(*) дофига весит

From: Alex Gorbachenko <agent_007(at)immo(dot)ru>
To: pgsql-ru-general(at)postgresql(dot)org
Subject: Re: COUNT(*) дофига весит
Date: 2008-04-17 06:37:17
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-ru-general
On Wed, 16 Apr 2008 13:48:42 +0400
silly_sad wrote:

>Объясните пожалуйста, в чем разница между авто и еженочным vaccuum

в том, что autovacuum проверяет количество измененных
записей в таблицах, и запускается в случае, если это количество >
некоего числа. что позволяет "размазать" вакуум по времени. по моему в
документации это написано довольно подробно.


"When enabled, the autovacuum daemon runs periodically and checks for
tables that have had a large number of inserted, updated or deleted

"Tables whose relfrozenxid value is more than autovacuum_freeze_max_age
transactions old are always vacuumed. Otherwise, two conditions are
used to determine which operation(s) to apply. If the number of
obsolete tuples since the last VACUUM exceeds the "vacuum threshold",
the table is vacuumed."

np: Alter Bridge - Before Tomorrow Comes

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