Lock Table

A lock is created when a user thread writes an entry in the lock table. The lock table is the pool of available locks. Each lock is 44 bytes. A single transaction can own multiple locks. For an explanation of locking and the SQL statements associated with locking, see the IBM Informix Guide to SQL: Tutorial.

The following information, which is stored in the lock table, describes the lock:

• The address of the transaction that owns the lock
• The type of lock (exclusive, update, shared, byte, or intent)
• The page and rowid that is locked
• The tblspace where the lock is placed
• Information about the bytes locked (byte-range locks for smart large objects):
  • Smart-large-object ID
  • Offset into the smart large object where the locked bytes begin
  • The number of bytes locked, starting at the offset

To specify the initial size of the lock table, set the LOCKS configuration parameter.

If the number of locks allocated by sessions exceeds the value of LOCKS, the database server doubles the size of the lock table, up to 15 times. The maximum value of LOCKS is 8,000,000. Use the DEF_TABLE_LOCKMODE configuration parameter to set the lock mode to page or row for new tables.

For more information on using and monitoring locks, see the chapter on locking in your IBM Informix Dynamic Server Performance Guide and the IBM Informix Guide to SQL: Tutorial. For more information on using LOCKS to specify the number of locks for a session, see the chapter on configuration parameters in the IBM Informix Dynamic Server Administrator's Reference and the chapter on configuration effects on memory utilization in your IBM Informix Dynamic Server Performance Guide.