From: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
---|---|
To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Kevin Grittner <kevin(dot)grittner(at)wicourts(dot)gov>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: CLOG contention |
Date: | 2011-12-21 16:24:28 |
Message-ID: | 1324484624-sup-2565@alvh.no-ip.org |
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Lists: | pgsql-hackers |
Excerpts from Robert Haas's message of mié dic 21 13:18:36 -0300 2011:
> There may be workloads where that will help, but it's definitely not
> going to cover all cases. Consider my trusty
> pgbench-at-scale-factor-100 test case: since the working set fits
> inside shared buffers, we're only writing pages at checkpoint time.
> The contention happens because we randomly select rows from the table,
> and whatever row we select hasn't been examined since it was last
> updated, and so it's unhinted. But we're not reading the page in:
> it's already in shared buffers, and has never been written out. I
> don't see any realistic way to avoid the CLOG lookups in that case:
> nobody else has had any reason to touch that page in any way since the
> tuple was first written.
Maybe we need a background "tuple hinter" process ...
--
Álvaro Herrera <alvherre(at)commandprompt(dot)com>
The PostgreSQL Company - Command Prompt, Inc.
PostgreSQL Replication, Consulting, Custom Development, 24x7 support
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