CURSOR_SHARING parameter

CURSOR_SHARING parameter

CURSOR_SHARING


What is cursor_sharing parameters ?
CURSOR_SHARING determines what kind of SQL statements can share the same cursors.

What is possible values for this parameter ?
1. EXACT (default)
Only allows statements with identical text to share the same cursor.

2. FORCE
Forces statements that may differ in some literals, but are otherwise identical, to share a cursor, unless the literals affect the meaning of the statement.

3. SIMILAR
Causes statements that may differ in some literals, but are otherwise identical, to share a cursor, unless the literals affect either the meaning of the statement or the degree to which the plan is optimized.

When we have to / should use this parameter ?
Whenever you have lots of some sql statement to execute but differ in liternal and your application is not design to use BIND VARIABLE that time you can use CURSOR_SHARING=FORCE to share cursor for every sql statement which differ only in literal.

Consider setting CURSOR_SHARING to SIMILAR or FORCE if both of the following questions are true:

Are there statements in the shared pool that differ only in the values of literals?
Is the response time low due to a very high number of library cache misses?


Tom Kyte said "cursor_sharing=force" is not permanent solution for performance it is use for temporary basis during developer fix there bug in application... instead of this parameter use BIND VARIABLE.

Performance improvement when we set cursor_sharing=force ?
When your application use lots of similar sql statement but differ in literal then yes performance will improve when you set cursor_sharing=force.

Side Effects on database when set cursor_sharing=FORCE/SIMILAR
Forcing cursor sharing among similar (but not identical) statements can have unexpected results in some DSS applications, or applications that use stored outlines.

Oracle does not recommend setting CURSOR_SHARING to FORCE in a DSS environment or if you are using complex queries. Also, star transformation is not supported with CURSOR_SHARING set to either SIMILAR or FORCE. For more information, see the "OPTIMIZER_FEATURES_ENABLE Parameter".

BUG with cursor_sharing=FORCE/SIMILAR
In Oracle Version 8i there is bug when set cursor_sharing=force/similar.

We need to down our database to set this parameter
No, we can set this parameter when our database is open.

alter system set CURSOR_SHARING=force SCOPE=both;