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The Present.....The Present.....
Notes:
Now we have 50-4K pools and 10-32K pools to tune the environments. The basic fact that IBM has given us this many pools should put to rest the misconception (that is still used in some IBM presentations) that one large pool is the best way to optimize overall performance. Naturally, every installation should start with one pool...and very quickly move to multiple pools to optimize performance and maximize DB2s use of memory. The dynamically adjustable thresholds (and pool sizes)have been sorely needed for many years. The default thresholds for the pools, as with most default values, are rarely correct for any installation. The first two that be altered immediately are VDWTH and DWTH. These should be set quite low to force updated page writes out of the system, and avoid major performance hiccups at checkpoint intervals. While percentages vary based on number of buffers, a low percentage for VWTH, setting the number of buffers as close as possible to (but not less than)128, will optimize DB2s use of the asynchronous write facility. DWTH should be reduced into the range of 25%, as long as the number of buffers is 2000 or more. The VPSEQT should be set quite low for pools dedicated to objects accessed randomly, but never quite to zero. This will allow some dynamic prefetch to occur, without seriously impacting the base usage of the pool.
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