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Oracle cursor_sharing=force tips

Oracle Database Tips by Donald Burleson

Some Oracle databases with high ad-hoc query activity (Crystal Reports, Business Objects) cannot avoid in-line literals inside the SQL, and that's why Oracle introduced the cursor_sharing parameter. The use of cursor_sharing=force has been shown to provide a huge benefit for database plagued with literals (i.e. non-reentrant SQL) in their library cache.

Also, note that in 11g, cursor_sharing=similar has been debugged to the point where it can be used.  See my notes on adaptive cursor sharing and include bind variable peeking.

The dynamic shop often has SQL that is generated by ad-hoc query tools with hard-coded literal values embedded within the SQL. As we know, hard-coded literal values make the SQL statements non-reusable unless cursor_sharing=force is set in the Oracle initialization file.

Shops that are plagued with non-reusable SQL can adopt either the persistent or the dynamic execution plan philosophy. To use optimizer plan stability with non-reusable SQL, the DBA will set cursor_sharing=force and then extract the transformed SQL from the library cache and use optimizer plan stability to make the execution plan persistent.

The dynamic shop often has SQL that is generated by ad-hoc query tools with hard-coded literal values embedded within the SQL. As we know, hard-coded literal values make the SQL statements nonreusable, unless  cursor_sharing=force is set in the Oracle initialization file. Shops that are plagued with nonreusable SQL can set  cursor_sharing=force.

Here is an example of cursor_sharing=force  benefiting an Oracle9i database that had experienced poor performance immediately after a new manufacturing plant was added to the existing database.

The cursor_sharing=force parameter was the only fast solution because the application was a vendor package with dynamically generated SQL and it could not easily be changed without using Optimizer Plan Stability (Stored Outlines), a very time-consuming task. 

Setting cursor_sharing=force greatly reduced the contention on the library cache and reduced CPU consumption.  The end users reported a 75 percent improvement in overall performance.

Here are some other notes on cursor_sharing=force and the cursor_sharing parameter:


 

If you like Oracle tuning, you may enjoy my new book "Oracle Tuning: The Definitive Reference", over 900 pages of my favorite tuning tips & scripts. 

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