Agenda
- Product Architecture
- Feature and Functionality
- Performance Self-Management Capabilities
- Benchmark Results and the Real World Proof Points
Locking and Concurrency Management
- Oracle’s superior multi-version read consistency model allows read and writes to be done independently
- IBM DB2 requires read locks
- Causes deadlocks, impacts scalability, increases administrative burden
- IBM DB2 requires read locks
- Oracle only requires locks for write activities
| “Locks are acquired even if your application merely reads rows, so it is still important to commit read-only units of work. This is because shared locks are acquired by repeatable read, read stability, and cursor stability isolation levels in read-only applications. With repeatable read and read stability, all locks are held until a COMMIT is issued, preventing other processes from updating the locked data, unless you close your cursor using the WITH RELEASE clause. In addition, catalog locks are acquired even in uncommitted read applications using dynamic SQL or XQuery statements.”
http://publib.boulder.ibm.com/infocenter/db2luw/v9r5/topic/com.ibm.db2.luw.admin.perf.doc/doc/c0005276.html |
Locking and Concurrency Management
- Oracle does not escalate locks
- IBM DB2 stores locks in memory and escalates locks from row to table level when out of memory
- Lock escalation increases the likelihood of deadlocks
- Oracle stores locks on disk
| “The amount of memory devoted to locking is controlled by the locklist database configuration parameter. If the lock list fills, performance can degrade due to lock escalations and reduced concurrency on shared objects in the database. If lock escalations occur frequently, increase the value of either locklist or maxlocks, or both. Also, to reduce number of locks held at one time, ensure that transactions COMMIT frequently to free held locks.”
http://publib.boulder.ibm.com/infocenter/db2luw/v9r5/topic/com.ibm.db2.luw.admin.perf.doc/doc/c0005266.html |
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