5486OpS.fm Draft Document for Review October 18, 2004526 IBM Eserver i5 and iSeries System Handbookperformance for both centralized and distributed client/server database access,making the iSeries the database server of choice for many computing needs.The following DB2 UDB for iSeries functions are available to enhance applicationperformance: Advanced SQL optimizerThis optimizer converts SQL requests into optimally efficient database accessmethods, using proven mathematical rules and to query specific costestimates. Optimal performance is maintained over time by the automaticrebind feature, which redetermines access methods based on changes to thedatabase objects and statistics. The optimizer detects changes in the numberof processors on each query. When processors are moved to an LPAR orwhen Capacity Upgrade on Demand adds additional processors, the queryplan is automatically re-optimized if necessary. SQL encoded vector indexes (EVIs)An EVI can be created through SQL and improve query performance,especially for long-running queries that run against large files using manyselection criteria. An EVI has several advantages over a traditional index withthe same keys, for example:– Precise statistics about the distribution of key values are automaticallymaintained and can be accessed quicker by the query optimizer thantraditional indexes.– EVIs can be built much faster and take significantly less storage thantraditional indexes. Less storage means less main storage is necessary torun the query.– The query optimizer can scan EVIs and dynamically build bitmaps quickerthan from traditional indexes. Explain functionThe Explain function examines and reports the access method used byindividual SQL queries. The output can be examined to determine whetherthe access method generated for the query can be improved by query ordatabase changes. Block INSERT and FETCHBlock Insert and Fetch provides applications with the ability to store andretrieve arrays of data directly, instead of one row at a time. Automatic record blockingAn automatic recording blocking function improves client/server performanceby returning rows to the client in blocks rather than individually. Subsequent
