From: | PFC <lists(at)peufeu(dot)com> |
---|---|
To: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Load Distributed Checkpoints test results |
Date: | 2007-06-15 20:42:33 |
Message-ID: | op.ttzc47iicigqcu@apollo13 |
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Lists: | pgsql-hackers |
On Fri, 15 Jun 2007 22:28:34 +0200, Gregory Maxwell <gmaxwell(at)gmail(dot)com>
wrote:
> On 6/15/07, Gregory Stark <stark(at)enterprisedb(dot)com> wrote:
>> While in theory spreading out the writes could have a detrimental
>> effect I
>> think we should wait until we see actual numbers. I have a pretty strong
>> suspicion that the effect would be pretty minimal. We're still doing
>> the same
>> amount of i/o total, just with a slightly less chance for the elevator
>> algorithm to optimize the pattern.
>
> ..and the sort patching suggests that the OS's elevator isn't doing a
> great job for large flushes in any case. I wouldn't be shocked to see
> load distributed checkpoints cause an unconditional improvement since
> they may do better at avoiding the huge burst behavior that is
> overrunning the OS elevator in any case.
...also consider that if someone uses RAID5, sorting the writes may
produce more full-stripe writes, which don't need the read-then-write
RAID5 performance killer...
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