Re: Multixacts wraparound monitoring - Mailing list pgsql-general

From Alvaro Herrera
Subject Re: Multixacts wraparound monitoring
Date
Msg-id 20160331131646.GA98919@alvherre.pgsql
Whole thread Raw
In response to Re: Multixacts wraparound monitoring  ("Pavlov, Vladimir" <Vladimir.Pavlov@tns-global.ru>)
Responses Re: Multixacts wraparound monitoring  ("Pavlov, Vladimir" <Vladimir.Pavlov@tns-global.ru>)
List pgsql-general
Pavlov, Vladimir wrote:
> Hello,
> If I get you right:
> Latest checkpoint's NextMultiXactId:      2075246000
> Latest checkpoint's oldestMultiXid:       2019511697
> Number of members files:    10820
> Size pg_multixact/members/ (bytes) (2.7Gb):    2887696384
> Pages in file:    32
> Members on page:    2045
> Number of members (32*2045*10820):    708060800
> Members per multixact (2075246000 - 2019511697)/708060800:    12,70421916
> Multixact size (bytes) (2887696384/708060800):    4,078316981 - It's a lot?

Yeah, 12.7 members per multixact on average is a lot, unless you have 12
processes concurrently locking the same tuples, all the time (although
that is possible).   My guess is that this is related to subtransactions
(either explicit SAVEPOINTs in your SQL code, or EXCEPTION blocks in
plpgsql functions).

--
Álvaro Herrera                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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