| From: | "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com> |
|---|---|
| To: | "Csaba Nagy" <nagy(at)ecircle-ag(dot)com> |
| Cc: | "Gregory Stark" <stark(at)enterprisedb(dot)com>, "Decibel!" <decibel(at)decibel(dot)org>, <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: Linux mis-reporting memory |
| Date: | 2007-09-21 10:34:53 |
| Message-ID: | 46F39E4D.1080401@enterprisedb.com |
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| Thread: | |
| Lists: | pgsql-performance |
Csaba Nagy wrote:
> On Fri, 2007-09-21 at 10:43 +0100, Gregory Stark wrote:
>> The other possibility is that Postgres just hasn't even touched a large part
>> of its shared buffers.
>
> But then how do you explain the example I gave, with a 5.5GB table
> seq-scanned 3 times, shared buffers set to 12 GB, and top still showing
> almost 100% memory as cached and no SWAP "used" ? In this case you can't
> say postgres didn't touch it's shared buffers - or a sequential scan
> won't use the shared buffers ?
Which version of Postgres is this? In 8.3, a scan like that really won't
suck it all into the shared buffer cache. For seq scans on tables larger
than shared_buffers/4, it switches to the bulk read strategy, using only
a few buffers, and choosing the starting point with the scan
synchronization facility.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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