| From: | "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> |
|---|---|
| To: | "Greg Smith" <greg(at)2ndquadrant(dot)com>, "Jon Nelson" <jnelson+pgsql(at)jamponi(dot)net> |
| Cc: | "Vitalii Tymchyshyn" <tivv00(at)gmail(dot)com>, "david(at)lang(dot)hm" <david(at)lang(dot)hm>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>, "Craig Ringer" <craig(at)postnewspapers(dot)com(dot)au>, <mladen(dot)gogala(at)vmsinfo(dot)com> |
| Subject: | Re: Slow count(*) again... |
| Date: | 2010-10-12 15:29:22 |
| Message-ID: | 4CB43882020000250003681C@gw.wicourts.gov |
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| Lists: | pgsql-hackers pgsql-performance |
Jon Nelson <jnelson+pgsql(at)jamponi(dot)net> wrote:
> Greg Smith <greg(at)2ndquadrant(dot)com> wrote:
>> Usually the sequence used to remove all cached data from RAM
>> before a benchmark is:
>
> All cached data (as cached in postgresql - *not* the Linux system
> caches)..., right?
No. The stop and start of PostgreSQL causes empty PostgreSQL
caches. These lines, in between the stop and start, force the Linux
cache to be empty (on recent kernel versions):
sync
echo 3 > /proc/sys/vm/drop_caches
-Kevin
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