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DBA CORNER
LOCK CONTENTION ISSUES can be frustrating problems to investigate and debug. But any time a database system is involved, the potential exists for locking to cause concurrency problems. Before blaming the database system (as is the usual response), try to answer the following questions to help identify the cause of the locking problems:
* Has the application run in the past without locking problems?
* Have the lock timeouts or deadlocks started recently?
* What version and level of the DBMS are you running?
* Does the problem only occur at certain times?
* What has changed on the system (e.g., number of users, number of applications, amount of data in the tables, database maintenance/ fixpacks, changes to any other relevant software, etc.)?
* What, if anything, has changed in the application (e.g., isolation level, concurrent executions, volume of data, etc.)?
When one application program tries to read data that's in the process of being changed by another, the DBMS must control access until the modification is complete to ensure data integrity. Typically, DBMS products use a locking mechanism to control access and modifications while ensuring data integrity.
This mechanism must be capable of differentiating between...