From: | Andrew Sullivan <ajs(at)crankycanuck(dot)ca> |
---|---|
To: | pgsql-sql(at)postgresql(dot)org |
Subject: | Re: INSERT waiting under heavy load |
Date: | 2006-01-08 18:21:14 |
Message-ID: | 20060108182114.GA31582@phlogiston.dyndns.org |
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Lists: | pgsql-sql |
On Fri, Jan 06, 2006 at 04:49:09PM -0500, Tom Lane wrote:
> performance risk in the sort of scenario you are describing.
> (I'm not sure why it would manifest as transactions showing "INSERT
> waiting" state though.)
It's because of I/O. When you have a large number of updates, the
planner always assumes an indexscan (correctly), but you end up
scanning megabytes of dead tuples. With a large number of open
transactions, most of the time VACUUM can't recover the space. I
agree with what Tom said earlier in this thread: the design is
guaranteed to lose.
A
--
Andrew Sullivan | ajs(at)crankycanuck(dot)ca
"The year's penultimate month" is not in truth a good way of saying
November.
--H.W. Fowler
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