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  3. August 2013

Re: Index Selection

On 09 Aug 2013 11:56, Michael Ryan wrote:
Ok...two systems, both on 7.1. Execute STRDBG UPDPROD(*YES). Run a
program on system A. Job log shows an index was used for bit map
processing. Run the same program on system B. Same index in place
(though different libraries). System B job log says arrival sequence
was used. How can I figure out why the index is used on one system
and not the other? Thanks!

High cardinality of the data being selected via the index would discourage use of the index because random I\O would tend to be slower than sequential given sufficient memory exists to smoothly page the data. The OPTIMIZE FOR n ROWS clause for the query can influence the optimizer. Another debug message should indicate if the query timed-out in looking for another index, or what reason the index was not used if it had been interrogated.


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