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Re: Visibility map, partial vacuums

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Visibility map, partial vacuums
Date: 2008-11-20 13:29:48
Message-ID: 4925664C.3090605@enterprisedb.com (view raw or flat)
Thread:
Lists: pgsql-hackers
I committed the changes to FSM truncation yesterday, that helps with the 
truncation of the visibility map as well. Attached is an updated 
visibility map patch.

There's two open issues:

1. The bits in the visibility map are set in the 1st phase of lazy 
vacuum. That works, but it means that after a delete or update, it takes 
two vacuums until the bit in the visibility map is set. The first vacuum 
removes the dead tuple, and only the second sees that there's no dead 
tuples and sets the bit.

2. Should modify the output of VACUUM VERBOSE to say how many pages were 
actually scanned. What other information is relevant, or is no longer 
relevant, with partial vacuums.

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com

Attachment: visibilitymap-2.patch
Description: text/x-diff (48.2 KB)

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