| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | fred(at)redhotpenguin(dot)com |
| Cc: | Bobbie van der Westhuizen <Bobbie(at)idpi1(dot)agric(dot)za>, pgsql-general(at)postgresql(dot)org, tomcat(at)designmagick(dot)com |
| Subject: | Re: updates (postgreSQL) very slow |
| Date: | 2004-03-11 07:01:15 |
| Message-ID: | 16835.1078988475@sss.pgh.pa.us |
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| Lists: | pgsql-general |
Fred Moyer <fred(at)redhotpenguin(dot)com> writes:
> On Wed, 2004-03-10 at 15:30, Tom Lane wrote:
>> A while, sure, but 2 hours seems excessive to me too.
> If there are no foreign keys or triggers and updating each row is taking
> one drive seek ( approximately 9 ms with the 80 gig IDE drive being used
> here ) then to do 747524 seeks will take 6727716 ms, about 10% less than
> the time of 7628686 ms for the update above. Is this is an accurate
> estimate or are these numbers just coincidence?
Probably coincidence. There's no reason to think that a large UPDATE
would expend one disk seek per updated row on average --- there's enough
buffering between the UPDATE and the drive heads that under normal
circumstances the cost should be lots less.
If I had to bet at this point I'd bet on inefficient foreign-key checks,
but since we haven't seen any schema details that's purely speculation.
regards, tom lane
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