Oracle-L: RE: Checking the rebuildability of an index

From: <Jared.Still_at_radisys.com>
Date: Tue, 06 Aug 2002 13:58:25 -0800
Message-ID: <F001.004ACB9A.20020806135825@fatcity.com>

I don't do it often, but there are times that it's needed.

One I rebuilt recently went from 68 Meg to ~30 meg. This makes a significant reduction in time spent scanning that index, and reduces pressure on the cache buffer.

Most may not need rebuilt often, but you should be able to point at data telling you which ones should be rebuilt, which ones shouldn't be rebuilt, and why.

There's also the political CYA factor, such as the hot shot consultant that's checking out your systems and wants to know why your indexes haven't been rebuilt, or your buffer hit ratio is 65%, and then proceeds to report to management that you aren't doing your job.

You need to have convincing answers for these questions, backed up by data.

Jared

"Post, Ethan" <Ethan.Post_at_ps.net>
Sent by: root_at_fatcity.com
08/06/2002 11:38 AM
Please respond to ORACLE-L

        To:     Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
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        Subject:        RE: Checking the rebuildability of an index

If memory serves correct (and it might not) both Tom Kyte and Jonathan Lewis
have stated that in most circumstances rebuilding indexes is useless. I think Tom may have said he could count the # of times he had to rebuild an index on one hand (something like that). Thus, I have stopped worrying about this one so much and will only entertain rebuilds if I start to see performance issues. Of course if you have the time and need to look busy keep rebuilding those indexes :)

By the way the reason it is useless is not that there is never a performance
gain but that most indexes that need to be rebuild quickly degrade again and
the period that one experiences a performance gain is minimal. Operating off a poor memory here so hopefully I have not misrepresented anyone.

Ethan Post
perotdba (AIM), epost1 (Yahoo)

-----Original Message-----
Sent: Tuesday, August 06, 2002 1:05 PM
To: Multiple recipients of list ORACLE-L

Actually, I do the 'validate structure' as well, and neglected to include it in my previous post.

Jared

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Author: Rajesh Dayal
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Author: Post, Ethan
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