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Proposal for Performance improvement for unique checks

From: Gokulakannan Somasundaram <gokul007(at)gmail(dot)com>
To: pgsql-hackers list <pgsql-hackers(at)postgresql(dot)org>
Subject: Proposal for Performance improvement for unique checks
Date: 2010-03-27 07:11:32
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Lists: pgsql-hackers
I don't think this should involve much code change. But no-one

On Sat, Mar 27, 2010 at 2:23 AM, Gokulakannan Somasundaram <
gokul007(at)gmail(dot)com> wrote:

> Hi,
>    Since we insert a new entry into the index for every update that's being
> made into the table, we inevitably make a unique check against the older
> version of the newly inserted row, even when the values are not updated. Of
> course i am talking about non-HOT updates. (We will not go to the index for
> HOT updates)
> a) The page which contains the index entry is Exclusively locked
> b) We go ahead and visit the heap page for its HeapTupleSatisfiesDirty.
> If we have the information of the old tuple(its tuple-id) after a heap
> update, during the index insert, we can avoid the uniqueness check for this
> tuple,as we know for sure that tuple won't satisfy the visibility criteria.
> If the table has 'n' unique indexes it avoids 'n' heap tuple lookups, also
> increasing the concurrency in the btree, as the write lock duration is
> reduced.
> Any comments?
> Thanks,
> Gokul.


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