From: Decibel! <decibel@decibel.org>
To: Merlin Moncure <mmoncure@gmail.com>
Cc: Mark Makarowsky <bedrockconstruction@yahoo.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Update table performance
Date: Thu, 9 Aug 2007 10:32:15 -0500
Message-ID: <20070809153215.GQ20424@nasby.net> (raw)
In-Reply-To: <b42b73150708090534n3c5dfba6qbabf6dc1b2e0011e@mail.gmail.com>
References: <20070807214227.GR25704@nasby.net>
<670773.87500.qm@web32209.mail.mud.yahoo.com>
<b42b73150708090534n3c5dfba6qbabf6dc1b2e0011e@mail.gmail.com>
On Thu, Aug 09, 2007 at 06:04:09PM +0530, Merlin Moncure wrote:
> That said, 'update' is the slowest operation for postgresql relative
> to other databases that are not MVCC.
Actually, it depends on how you do MVCC. In Oracle, DELETE is actually
the most expensive operation, because they have to not only remove the
row from the heap, they have to copy it to the undo log. And they need
to do something with indexes as well. Whereas we just update 4 bytes in
the heap and that's it.
An UPDATE in Oracle OTOH just needs to store whatever fields have
changed in the undo log. If you haven't messed with indexed fields, it
doesn't have to touch those either.
--
Decibel!, aka Jim Nasby decibel@decibel.org
EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
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To: pgsql-performance@postgresql.org
Cc: decibel@decibel.org, mmoncure@gmail.com, bedrockconstruction@yahoo.com
Subject: Re: Update table performance
In-Reply-To: <20070809153215.GQ20424@nasby.net>
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