Exclusive Lock Escalations

Snapshot Information Level
Database
Application

API Structure(s)
sqlm_dbase
sqlm_appl

Monitor Group
Basic
Basic

Resettable

Yes

Event Information Level
Database
Connection
Transaction

API Structure(s)
sqlm_db_event
sqlm_conn_event
sqlm_xaction_event

API Element Name
Element Type

x_lock_escals
counter

Description:  The number of times that locks have been escalated from several row locks to one exclusive table lock, or the number of times an exclusive lock on a row caused the table lock to become an exclusive lock.

Usage:  Other applications cannot access data held by an exclusive lock; therefore it is important to track exclusive locks since they can impact the concurrency of your data.

A lock is escalated when the total number of locks held by an application reaches the maximum amount of lock list space available to the application. The amount of lock list space available is determined by the locklist and maxlocks configuration parameters.

When an application reaches the maximum number of locks allowed and there are no more locks to escalate, it will then use space in the lock list allocated for other applications. When the entire lock list is full, an error occurs.

There are several possible causes for excessive exclusive lock escalations:

• The lock list size (locklist) may be too small for the number of concurrent applications.
• The percent of the lock list usable by each application (maxlocks) may be too small.
• One or more applications may be using an excessive number of locks.
• An application may be using exclusive locks when share locks are sufficient. Although share locks may not reduce the total number of lock escalations (see "Lock Escalations"), share lock escalations may be preferable to exclusive lock escalations.

To resolve these problems, you may be able to:

• Increase the locklist configuration parameter value. See the Administration Guide for a description of this configuration parameter.
• Increase the maxlocks configuration parameter value. See the Administration Guide for a description of this configuration parameter.
• Identify the applications with large numbers of locks (see "Maximum Number of Locks Held"). These applications can also cause lock escalations in other applications by using too large a portion of the lock list. They may need to resort to using table locks instead of row locks, although table locks may cause an increase in "Lock Waits" and "Time Waited On Locks".

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