RE: How many is too many

  • From: "Taylor, Chris David" <ChrisDavid.Taylor@xxxxxxxxxxxxxxx>
  • To: "'veeeraman@xxxxxxxxx'" <veeeraman@xxxxxxxxx>, 'ORACLE-L' <oracle-l@xxxxxxxxxxxxx>
  • Date: Fri, 12 Aug 2011 06:58:57 -0500

Sometimes, a "good" index causes exceptionally bad performance.  We have a 
situation where if I add, what I "think" is, a good index on paper, the 
execution plan changes in such a way as to make subsequent queries perform 
horribly.  The physical I/O looks good, the cost looks good, but the logical 
I/O goes berserk.

Chris Taylor
Sr. Oracle DBA
Ingram Barge Company
Nashville, TN 37205
Office: 615-517-3355
Cell: 615-663-1673
Email: chris.taylor@xxxxxxxxxxxxxxx<mailto:chris.taylor@xxxxxxxxxxxxxxx>

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From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On 
Behalf Of Ram Raman
Sent: Thursday, August 11, 2011 3:45 PM
Subject: How many is too many


  I am looking at a table in our system and it has 12 indexes, we are planning 
on adding another one. I am aware of the effects of having too many indexes, 
but in this case adding an extra index helps a certain query that runs slow. 
Other queries and most other operations against the table are acceptable too. I 
see a few tables like this; is there a number above which is considered a no-no 
when it comes to adding more indexes.

PS. The tables and queries are structured in a way that seem to require several 
indexes - it is a third party product.


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