RE: Why my query plan changed ?
Date: Wed, 17 Sep 2008 11:01:18 -0500
Message-ID: <3B8B6A1700202C43A89D61CE495C894E0F4DF9976C@MSPM1BMSGM103.ent.core.medtronic.com>
What you are seeing is the feature called bind variable peeking. The first time a query hits the shared pool, the optimizer check the value of the bind variables and then uses these variables to build the query plan. If the query gets aged out of the shared pool, then this process is repeated with possibly new bind variable values. As a result the query plan changes. The query plan changes less with cursor_sharing=force than with cursor_sharing=exact since cursor_sharing=exact does not replace literals with bind variables.
Pat
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Dennis Williams Sent: Wednesday, September 17, 2008 8:48 AM To: ajayoraclel_at_yahoo.com
Cc: jaromir_at_db-nemec.com; oracle-l_at_freelists.org Subject: Re: Why my query plan changed ?
Ajay,
I haven't worked with CURSOR_SHARING, so I cannot give you an answer based on experience, but just speculation. Perhaps someone else on the list has better advice.
Since the goal of CURSOR_SHARING=FORCE is to avoid continual parsing and optimizing, I would assume that when you submit a SQL statement to Oracle, it is first converted to an equivalent statement with bind variables, and then Oracle will search for an existing equivalent SQL statement, and if it finds one, will use that execution plan. Therefore in answer to your question, I would assume that CURSOR_SHARING=FORCE would have the same side effect, that whatever execution plan is generated, all subsequent queries will share it.
Dennis Williams
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