Re: Slow count(*) again... - Mailing list pgsql-performance

From Kevin Grittner
Subject Re: Slow count(*) again...
Date
Msg-id 4CB43882020000250003681C@gw.wicourts.gov
Whole thread Raw
In response to Re: Slow count(*) again...  (Jon Nelson <jnelson+pgsql@jamponi.net>)
List pgsql-performance
Jon Nelson <jnelson+pgsql@jamponi.net> wrote:
> Greg Smith <greg@2ndquadrant.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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