| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Peter Geoghegan <pg(at)bowt(dot)ie>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Fsync request queue |
| Date: | 2018-05-01 17:43:14 |
| Message-ID: | CA+Tgmoa9ZLSuOnuYbAAnGJnfUyRWrY9uLUpCsE31hCEC3LonwA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, May 1, 2018 at 1:41 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> I unfortunately don't have access to the relevant reports anymore, so
> it's only by memory. What I do remember is that a few I saw
> pg_stat_bgwriter.buffers_backend_fsync values that we a pretty sizable
> fraction of the buffers written by backends. I don't think I ever
> figured out how problematic that was from a peformance perspective, and
> how large a fraction of the overall number of fsyncs those were.
>
> One was a workload with citus (lots of tables per node), and one was
> inheritance based partitioning. There were a few others too, where I
> don't recall anything about the workload.
Hmm. Partitioning probably does make it easier to overrun the queue,
but even so it seems hard -- the queue has one entry per shared
buffer, which is a lot.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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