| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Dave Chinner <david(at)fromorbit(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Jim Nasby <jim(at)nasby(dot)net>, Mel Gorman <mgorman(at)suse(dot)de>, Josh Berkus <josh(at)agliodbs(dot)com>, Kevin Grittner <kgrittn(at)ymail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, Joshua Drake <jd(at)commandprompt(dot)com>, "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: | 2014-01-16 00:29:00 |
| Message-ID: | CA+TgmoauXJHriweF=7zoQUF9wJ4UxTxPJ8Fx-QRp+5xw1-BAVg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Jan 15, 2014 at 7:22 PM, Dave Chinner <david(at)fromorbit(dot)com> wrote:
> No, I meant the opposite - in low memory situations, the system is
> going to go to hell in a handbasket because we are going to cause a
> writeback IO storm cleaning memory regardless of these IO
> priorities. i.e. there is no way we'll let "low priority writeback
> to avoid IO storms" cause OOM conditions to occur. That is, in OOM
> conditions, cleaning dirty pages becomes one of the highest priority
> tasks of the system....
I don't see that as a problem. What we're struggling with today is
that, until we fsync(), the system is too lazy about writing back
dirty pages. And then when we fsync(), it becomes very aggressive and
system-wide throughput goes into the tank. What we're aiming to do
here is get is to start the writeback sooner than it would otherwise
start so that it is spread out over a longer period of time.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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