SQL Server Stored Procedures Optimization Tips
January 8, 2003
Here are twelve helpful tips for ensuring that you've constructed your SQL Server stored procedures to perform in the most efficient manner possible.
This can reduce network traffic as your client will send to the server only the stored procedure name (perhaps with some parameters) instead of all the text from a large heavy-duty query. Stored procedures can be used to enhance security and conceal underlying data objects as well. For example, you can give the users permission to execute the stored procedure to work with restricted sets of columns and data.
This can reduce network traffic due to the fact that your client will not receive the message indicating the number of rows affected by a Transact-SQL statement.
The complete name of an object consists of four identifiers: the server name, database name, owner name, and object name. An object name that specifies all four parts is known as a fully qualified name.
Using fully qualified names eliminates any confusion about which stored procedure you want to run and can boost performance because SQL Server has a better chance to reuse the stored procedures execution plans if they were executed using fully qualified names.
The RETURN statement exits unconditionally from a stored procedure, so the statements following RETURN are not executed. Though the RETURN statement is generally used for error checking, you can use this statement to return an integer value for any other reason. Using the RETURN statement can boost performance because SQL Server will not create a recordset.
The prefix "sp_" is used in the system stored procedures names. Microsoft does not recommend using the prefix "sp_" in user-created stored procedure names as SQL Server always looks for a stored procedure beginning with "sp_" in the following order: the master database, the stored procedure based on the fully qualified name provided, followed by the stored procedure using dbo as the owner (if one is not specified).
When you have the stored procedure with the prefix "sp_" in a database other than master, the master database is always checked first. If the user-created stored procedure has the same name as a system stored procedure, the user-created stored procedure will never be executed.
The sp_executesql stored procedure supports parameters. So, using the sp_executesql stored procedure instead of the EXECUTE statement improves readability of your code when many parameters are used.
When you use the sp_executesql stored procedure to execute a Transact-SQL statement that will be reused many times, the SQL Server query optimizer will reuse the execution plan it generates for the first execution when the change in parameter values to the statement is the only variation.
Microsoft recommends using temporary stored procedures when connecting to earlier versions of SQL Server that do not support the reuse of execution plans. Applications connecting to SQL Server 7.0 or SQL Server 2000 should use the sp_executesql system stored procedure instead of temporary stored procedures in order to have a better chance of reusing the execution plans.
The stored procedure will be recompiled when any structural changes are made to a table or view referenced by the stored procedure (an ALTER TABLE statement, for example), or when a large number of INSERTS, UPDATES or DELETES are made to a table referenced by a stored procedure. So, if you break down a very large stored procedure into several sub-procedures, there's a chance that only a single sub-procedure will be recompiled, while other sub-procedures will not.
Using temporary tables inside stored procedures reduce the chance to reuse the execution plan.
Using DDL statements inside stored procedures also reduce the chance to reuse the execution plan.
The WITH RECOMPILE option prevents reusing the stored procedure execution plan, so SQL Server does not cache a plan for this procedure and the procedure is always recompiled at run time. Using the WITH RECOMPILE option can boost performance if your query will vary each time it is run from the stored procedure, because in this case the wrong execution plan will not be used.
To check if a stored procedure has been recompiled, run SQL Server Profiler and choose to trace the event in the "Stored Procedures" category called "SP:Recompile". You can also trace the event "SP:StmtStarting" to see at what point in the procedure it is being recompiled. When you identify these stored procedures, you can take some correction actions to reduce or eliminate the excessive recompilations.