Application developers frequently need to retrieve a limited number of qualifying rows from a table. For example, maybe you need to list the top ten best selling items from inventory, or a list of the top five most expensive products (i.e., highest price tag). There are several ways to accomplish this prior to DB2 V7 using SQL, but they are not necessarily efficient.The first reaction is to simply use the WHERE clause to eliminate non-qualifying rows. But this is simplistic, and often is not sufficient to produce the results desired in an optimal...
Thursday, 24 September 2009
Friday, 4 September 2009
Dynamic SQL Causing Lock Escalation?
Posted on 11:20 by Unknown
Lock escalation is the promotion of a lock from a row, page or LOB lock to a table space lock because the number of page locks that are concurrently held on a given resource exceeds a preset limit.But lock escalation can cause problems. Yes, when fewer locks are taken, CPU cost and memory usage can be reduced. On the other hand, escalating the size of a lock causes more resources to be locked... and that impacts concurrency with the most likely result being applications experiencing lock timeouts or deadlocks.When lock escalation occurs, DB2 writes...
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