Re: An ancient mystery

From: Andrew Kerber <>
Date: Thu, 20 Nov 2008 21:51:36 -0600
Message-ID: <>

Is it possible someone gathered stats on the table, so the query went into CBO mode, and came up with a bad plan? Other than that, as I recall about the only thing that can go wrong with RBO is a bad index. But I would have expected that to throw an error message.

On Thu, Nov 20, 2008 at 9:05 PM, Dennis Williams <> wrote:

> List,
> The situation:
> Oracle database on Solaris 8 (soon to be upgraded to 10g)
> Rule-based Optimizer
> A query which has run for years using an indexed access to a very large
> table (maybe 100 million rows)
> suddenly decides to use a full-table scan, shutting down a critical
> business process.
> Then after several hours, it switches back to using the index.
> All concerned claim that nothing changed before or after.
> Needless to say the business users are nervous. They think maybe the
> database grew beyond some limit.
> Can anyone think of an explanation?
> Thanks,
> Dennis Williams

Andrew W. Kerber

'If at first you dont succeed, dont take up skydiving.'

Received on Thu Nov 20 2008 - 21:51:36 CST

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