| From: | Stephen Frost <sfrost(at)snowman(dot)net> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Jan Kara <jack(at)suse(dot)cz>, Kevin Grittner <kgrittn(at)ymail(dot)com>, Hannu Krosing <hannu(at)2ndquadrant(dot)com>, Dave Chinner <david(at)fromorbit(dot)com>, Andres Freund <andres(at)2ndquadrant(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, Trond Myklebust <trondmy(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, Joshua Drake <jd(at)commandprompt(dot)com>, James Bottomley <James(dot)Bottomley(at)hansenpartnership(dot)com>, Mel Gorman <mgorman(at)suse(dot)de>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "lsf-pc(at)lists(dot)linux-foundation(dot)org" <lsf-pc(at)lists(dot)linux-foundation(dot)org>, Magnus Hagander <magnus(at)hagander(dot)net> |
| Subject: | Re: [Lsf-pc] Linux kernel impact on PostgreSQL performance |
| Date: | 2014-01-14 19:27:44 |
| Message-ID: | 20140114192744.GZ2686@tamriel.snowman.net |
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| Lists: | pgsql-hackers |
* Robert Haas (robertmhaas(at)gmail(dot)com) wrote:
> I dunno what a typical checkpoint size is but I don't think you'll be
> exaggerating much if you imagine that everything that could possibly
> be dirty is.
This is not uncommon for us, at least:
checkpoint complete: wrote 425844 buffers (20.3%); 0 transaction log
file(s) added, 0 removed, 249 recycled; write=175.535 s, sync=17.428 s,
total=196.357 s; sync files=1011, longest=2.675 s, average=0.017 s
That's a checkpoint writing out 20% of 16GB, or over 3GB, and that's
just from one of the four postmasters running- we get this kind of
checkpointing happening on all of them. All told, it's easy for us to
want to write over 12GB during a single checkpoint period on this box.
(checkpoint_timeout is 5m, checkpoint_target is 0.9).
Thankfully, the box has 256G of RAM and so the shared buffers only use
up 25% of the RAM in the box. :)
I'm sure others could post larger numbers.
Thanks,
Stephen
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