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Re: Replication Syatem

From: "Pavan Deolasee" <pavan(dot)deolasee(at)gmail(dot)com>
To: "Gauri Kanekar" <meetgaurikanekar(at)gmail(dot)com>
Cc: "Greg Smith" <gsmith(at)gregsmith(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Replication Syatem
Date: 2008-04-29 11:25:38
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Lists: pgsql-performance
On Tue, Apr 29, 2008 at 4:35 PM, Gauri Kanekar
<meetgaurikanekar(at)gmail(dot)com> wrote:

> Do we need to do any special config changes or any other setting for HOT to
> work??

No. HOT is enabled by default, on all tables. There is no way and need
to disable it.

> Any special guideline to follow to make HOT working??

You can do couple of things to benefit from HOT.

1. HOT addresses a special, but common case where UPDATE operation
does not change any of the index keys. So check if your UPDATE changes
any of the index keys. If so, see if you can avoid having index
involving that column. Of course, I won't advocate dropping an index
if it would drastically impact your frequently run queries.

2. You may leave some free space in the heap (fillfactor less than
100). My recommendation would be to leave space worth of one row or
slightly more than that to let first UPDATE be an HOT update.
Subsequent UPDATEs in the page may reuse the dead row created by
earlier UPDATEs.

3. Avoid any long running transactions.


Pavan Deolasee

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