RE: Some experience using hash clusters?
- From: "Nelson, Allan" <anelson@xxxxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Wed, 23 Jun 2004 07:23:12 -0500
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@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Juan Carlos Reyes
Pacheco
Sent: Tuesday, June 22, 2004 4:43 PM
To: oracle-l@xxxxxxxxxxxxx
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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