Re: Tuning Advice

From: Jonathan Lewis <>
Date: Fri, 27 Apr 2018 17:54:54 +0000
Message-ID: <LO1P123MB09772BBA713FF199592E3E79A58D0_at_LO1P123MB0977.GBRP123.PROD.OUTLOOK.COM>

The commonest resolution of that type of problem is that "select" may be running under first_rows(n) optimization which changes to all_rows as soon as you change the query to "insert as select"; alternatively the plan for a distributed select can do some optimizations that "insert as distributed select" can't.

In your case, though, you say a CTAS is just as fast as a select - and in both the above CTAS would have the same problem as "insert as select".

This isn't just a case of your insert maintaining indexes while your CTAS doesn't have any indexes ?

Jonathan Lewis

From: <> on behalf of Sheehan, Jeremy <> Sent: 27 April 2018 16:50
Subject: Tuning Advice

Hello Gurus,

AIX 7.1 I have a query that runs fairly well. Takes about 8 minutes to run, nothing terrible about it (no huge FTS, joins seem to be in place correctly). When I try to do an insert into TABLE as SELECT, it picks a completely different execution plan and never finishes. The really odd thing is that it works great when using CTAS or initial creation of a MV.

Any suggestion on how I can have the optimizer not use a specific execution plan or any session level parameters that would have it use a different execution plan?

Thanks in advance!


Received on Fri Apr 27 2018 - 19:54:54 CEST

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