Re: Avoiding unnecessary reads in recovery

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Avoiding unnecessary reads in recovery
Date: 2007-04-25 21:49:42
Message-ID: 6236.1177537782@sss.pgh.pa.us
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Heikki Linnakangas <heikki(at)enterprisedb(dot)com> writes:
> Tom Lane wrote:
>> but it'd make it safe to use in non-WAL contexts (I think there are
>> other places where we know we are going to init the page and so a
>> physical read is a waste of time).

> Is there? I can't think of any. Extending a relation doesn't count.

No, but re-using a free page in an index does. I'm not sure which index
AMs know for sure the page is free, and which have to read it and check,
but I think there's at least some scope for that.

regards, tom lane

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