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Re: Dead Space Map for vacuum

From: "Jochem van Dieten" <jochemd(at)gmail(dot)com>
To: "ITAGAKI Takahiro" <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Dead Space Map for vacuum
Date: 2006-12-28 09:24:51
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
On 12/28/06, ITAGAKI Takahiro wrote:
> | [TODO item] Allow data to be pulled directly from indexes
> | Another idea is to maintain a bitmap of heap pages where all rows are
> | visible to all backends, and allow index lookups to reference that bitmap
> | to avoid heap lookups
> It is not done yet, but we can use DSM for this purpose. If the corresponding
> bit in DSM is '0', all tuples in the page are frozen and visible to all
> backends. We don't have to look up frozen pages only for visibiliby checking.

Does that really work in the absence of a retail index vacuum method?
What if the heap is already vacuumed, frozen and the bit for that page
in the DSM is set to '0', but the index still contains entries that
haven't been removed by a vacuum yet?


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