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Page at a time index scan

From: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
To: pgsql-patches(at)postgresql(dot)org
Subject: Page at a time index scan
Date: 2006-05-01 19:00:11
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-patches
Here's a patch that implements page at a time index scans discussed at 
pgsql-hackers earlier. See proposal 1 at:

It passes regression tests, and there's no known bugs. There's 
some minor issues I'd like to point out, though:

1. An index scan now needs to allocate enough memory to hold potentially a 
whole page worth of items. And if you use markpos/restrpos, twice that 
much. I don't know if that's an issue, but I thought I'd bring that up.

2. Vacuum is now done in one phase, scanning the index in physical order. 
That significantly speeds up index vacuums of large indexes that don't fit 
into memory. However, btbulkdelete doesn't know if the vacuum is a full or 
lazy one. The patch just assumes it's a lazy vacuum, but the API really 
needs to be changed to pass that information earlier than at vacuum_cleanup.

3. Before the patch, a scan would keep the current page pinned to keep 
vacuum from deleting the current item. The patch doesn't change that 
behaviour, but it now seems to me that even a pin is no longer needed.

The patch needs testing and review, to ensure it doesn't brake anything, 
and to see the effect on performance. It doesn't change disk layout or 
catalogs, so you can run it using the same data directory as with the 
unpatched version.

- Heikki


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Next:From: Heikki LinnakangasDate: 2006-05-01 19:02:54
Subject: Re: Page at a time index scan
Previous:From: Larry RosenmanDate: 2006-05-01 18:15:13
Subject: Re: Logging pg_autovacuum

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