Sunday, March 29, 2009

How to Minimize SQL Server Blocking

By default, blocking locks do not time out. The waiting connection waits until the lock is released, and the block is over. If you like, you can set a lock time-out so that a connection does not wait indefinitely for the blocking lock to be released. This is accomplished using the LOCK_TIMEOUT setting.

When the LOCK_TIMEOUT setting is used to set a maximum amount of time that a connection can wait for a blocking lock to go away, the connection with the lock that is causing the blocking problem is not affected, but the connection waiting for the block is halted and an error message is received. When this happens, error message 1222, "Lock request time-out period exceeded," is sent to the application.

This means that the application needs to include the appropriate error-handling code to deal with this situation and take the appropriate action, which includes rolling back the transaction. If the application does not know how to deal with this error message, and the transaction is not rolled back, it is possible that the application can continue as if the transaction was not automatically cancelled. Because of this, you should not use the LOCK-TIMEOUT setting unless your application(s) that will be affected by it know what to do when they receive this message from SQL Server.

The syntax for the SET LOCK_TIMEOUT is:

SET LOCK_TIMEOUT timeout_period

Where timeout_period is the number of milliseconds that a connection waits for a blocking lock to go away before an error is returned from SQL Server to the application. A value of -1 is the default, which means to wait indefinitely. A value of 0 tells SQL Server not to wait at all, and to return the error immediately.

This command is based on a per connection basis, and stays with the connection until the connection is broken, or a new SET LOCK_TIMEOUT command is issued. [7.0, 2000]

1 comment:

goHosting said...

what sql server version , you are using ?