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Re: extending relations more efficiently

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Jeroen Vermeulen <jtv(at)xs4all(dot)nl>
Cc: Andres Freund <andres(at)anarazel(dot)de>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: extending relations more efficiently
Date: 2012-05-02 12:14:36
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Lists: pgsql-hackers
On Wed, May 2, 2012 at 7:16 AM, Jeroen Vermeulen <jtv(at)xs4all(dot)nl> wrote:
> On 2012-05-01 22:06, Robert Haas wrote:
>> It might also be interesting to provide a mechanism to pre-extend a
>> relation to a certain number of blocks, though if we did that we'd
>> have to make sure that autovac got the memo not to truncate those
>> pages away again.
> Good point.  And just to check before skipping over it, do we know that
> autovacuum not leaving enough slack space is not a significant cause of the
> bottlenecks in the first place?

I'm not sure exactly what you mean by this: autovacuum doesn't need
any slack space.  Regular DML operations can certainly benefit from
slack space, both within each page and overall within the relation.
But there's no evidence that vacuum is doing too good a job cleaning
up the mess, forcing the relation to be re-extended.  Rather, the
usual (and frequent) complaint is that vacuum is leaving way too much
slack space - i.e. bloat.

Robert Haas
The Enterprise PostgreSQL Company

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