From: | Philip Warner <pjw(at)rhyme(dot)com(dot)au> |
---|---|
To: | Zeugswetter Andreas SB <ZeugswetterA(at)wien(dot)spardat(dot)at>, "'Tom Lane'" <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: AW: CommitDelay performance improvement |
Date: | 2001-02-27 10:18:09 |
Message-ID: | 3.0.5.32.20010227211809.0311d720@mail.rhyme.com.au |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
At 10:56 27/02/01 +0100, Zeugswetter Andreas SB wrote:
>
>> > I agree that 30k looks like the magic delay, and probably 30/5 would be a
>> > good conservative choice. But now I think about the choice of number, I
>> > think it must vary with the speed of the machine and length of the
>> > transactions; at 20tps, each TX is completing in around 50ms.
>
>I think disk speed should probably be the main factor.
>After the first run 30k/5 also seemed the best here, but running the test
>again shows, that the results are only reproducible after a new initdb.
>Anybody else see reproducible results without previous initdb ?
I think we want something that reflects the chance of a time-saving as a
result of a wait, which is why I suggested having each backend monitor
commits/sec, then basing the delay on some % of that number. eg. if
commits/sec = 1, then it's either low-load, or long tx's, in either case
CommitDelay won't help. Similarly, if we have 1000 commits/sec, then we
have a very fast system and/or disk, and CommitDelay of 10ms is clearly
glacial.
AFAICS, dynamically monitoring commits/sec (or a similar statistic) is
TOWTG, but in all cases we need to set a max on CommitDelay to prevent
individual TXs getting too long (although I am unsure if the latter is
*really* necessary, it is far better to be safe).
Note: commits/sec need to be kept for each backend so we can remove the
contribution of the backend that is considering waiting.
----------------------------------------------------------------
Philip Warner | __---_____
Albatross Consulting Pty. Ltd. |----/ - \
(A.B.N. 75 008 659 498) | /(@) ______---_
Tel: (+61) 0500 83 82 81 | _________ \
Fax: (+61) 0500 83 82 82 | ___________ |
Http://www.rhyme.com.au | / \|
| --________--
PGP key available upon request, | /
and from pgp5.ai.mit.edu:11371 |/
From | Date | Subject | |
---|---|---|---|
Next Message | Steffen Emil Thorkildsen | 2001-02-27 12:25:07 | Query precompilation? |
Previous Message | Zeugswetter Andreas SB | 2001-02-27 09:56:07 | AW: CommitDelay performance improvement |