| From: | Jeff Davis <pgsql(at)j-davis(dot)com> |
|---|---|
| To: | "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com> |
| Cc: | Bruce Momjian <bruce(at)momjian(dot)us>, Gregory Stark <stark(at)enterprisedb(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, pgsql-hackers(at)postgresql(dot)org, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com> |
| Subject: | Re: COMMIT NOWAIT Performance Option |
| Date: | 2007-02-28 20:17:02 |
| Message-ID: | 1172693822.13722.73.camel@dogma.v10.wvs |
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| Lists: | pgsql-hackers |
On Wed, 2007-02-28 at 14:54 -0500, Jonah H. Harris wrote:
> On 2/28/07, Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
> > That's 5 minutes of data, in the default configuration.
>
> Right, but I don't know anyone that keeps checkpoints at 5 minutes.
> At least not on OLTP configurations.
>
It's got a hard maximum of 1 hour. Also, the need to make checkpoints
far apart has been reduced with bgwriter. It will be further reduced
with the patch that allows people to tune the bgwriter for their needs.
Recovery has to run through all those WAL segments anyway. It's not like
we're making a 5 second recovery take 20 minutes, we'd be taking an
already long recovery and making it longer (I'm not sure how much
longer, but it can't be more than twice as long).
I'm not saying there's no cost, but the extra recovery cost seems lower
to me than the CRC cost on every data page read during operation.
Also, if we find an error, do we even have the ability to correct it? A
CRC doesn't tell us which pages were written and which weren't, so we
could detect the error but not correct it, right?
Regards,
Jeff Davis
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