RE: Why my query plan changed ?
- From: "Elliott, Patrick" <patrick.elliott@xxxxxxxxxxxxx>
- To: "oracledba.williams@xxxxxxxxx" <oracledba.williams@xxxxxxxxx>, "ajayoraclel@xxxxxxxxx" <ajayoraclel@xxxxxxxxx>
- Date: Wed, 17 Sep 2008 11:01:18 -0500
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@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of Dennis Williams
Sent: Wednesday, September 17, 2008 8:48 AM
To: ajayoraclel@xxxxxxxxx
Cc: jaromir@xxxxxxxxxxxx; oracle-l@xxxxxxxxxxxxx
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
[CONFIDENTIALITY AND PRIVACY NOTICE]
Information transmitted by this email is proprietary to Medtronic and is
intended for use only by the individual or entity to which it is addressed, and
may contain information that is private, privileged, confidential or exempt
from disclosure under applicable law. If you are not the intended recipient or
it appears that this mail has been forwarded to you without proper authority,
you are notified that any use or dissemination of this information in any
manner is strictly prohibited. In such cases, please delete this mail from your
records.
To view this notice in other languages you can either select the following link
or manually copy and paste the link into the address bar of a web browser:
http://emaildisclaimer.medtronic.com
Other related posts:
