Re: help on indexing strategies!
From: DAGMARA_at_DELPHI.COM <(DAGMARA_at_DELPHI.COM)>
Date: 28 Mar 1994 20:39:07 -0500
Message-ID: <2n80rr$2p8_at_news.delphi.com>
Date: 28 Mar 1994 20:39:07 -0500
Message-ID: <2n80rr$2p8_at_news.delphi.com>
Just a few ideas off the top of my head:
- Look at the amount of data you are retrieving for each query; if the the data retrieved is greater than 25% of the records (I actually use a 15% value) then do NOT use the index; index usage increases your overhead too much.
- You want a high selectivity for your index; the more unique the better.
- I assume you have your indices in a separate tablespace, on a separate device, and perhaps striped.
- Choose the keys with the level of selectivity and/or the most frequently used columns as the leading edge of your concatenated indices.
- The cost-based optimizer is as good as the statistics that go into it.
Try getting the _ORACLE Performance Tuning Guide_ by (I think) Tom Horrigan. There is a nice discussion of these issues.
Dagmar Anne
Kopania & Komorowski
Richardson, TX
Received on Tue Mar 29 1994 - 03:39:07 CEST