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RE: Some experience using hash clusters?

From: Nelson, Allan <anelson_at_miswaco.com>
Date: Wed, 23 Jun 2004 07:23:12 -0500
Message-ID: <7E0DB3A126BA9146AC30744E2B7E42451118F6@midhouhqxch01.net.smith.com>


Not experience but I did attend a class that Steve Adams taught and in terms of Lookup tables he indicated that there were some circumstances where a hash cluster with a primary key index would offer some scope for performance improvement.

Did you note all the qualifiers in the sentence above=3F His analysis was based on keeping a single row per hash key in the cluster which gave the best access path performance. I won't say more as he teaches the class
=66or profit.

On a different note, I have had a number of my preconceptions shattered that were based on statements of the form: For all uses, feature x is a bad idea. Circumstances vary widely. Only accurate analysis suffices to show that in a given set of circumstances feature x does not provide a good match.

In regard to your specific comments below iff you can guarantee that a hash key points to a single row then you have demonstrated that i/o is minimized as you will do a single block read assuming no block chaining due to row length.

Allan

-----Original Message-----
=46rom: oracle-l-bounce_at_freelists.org

[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Juan Carlos Reyes Pacheco
Sent: Tuesday, June 22, 2004 4:43 PM
To: oracle-l_at_freelists.org
Subject: Some experience using hash clusters=3F

Hi list,
some time ago I knew using clusters was not a good idea. Now I read hash clusters can reduce i/o because no index lookup are necessary.

Could you please share your experience aobut the use of hash cluster.

Thanks
=20



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Received on Wed Jun 23 2004 - 07:20:37 CDT

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