December 30, 1999 11:55 AM
(in response to Mike Toppins)
The optimizer looks through the query and table statistics at a
to determine costs for the query, then uses the access paths which
the lowest total cost.
There are significant differences from version to version and
For a meaningful description, start with the Administration Guide
Your Queries" for some of the most common situtations and tuning.
see the statistics in a bit more detail, that's in the
Statistics in the
Catalog" chapter. To look at detailed analysis, then there is the
to improve SQL Performance" chapter.
Every release has a red book that discusses the optimizer
some measurements. There are classes from IBM and others.
"Toppins, Mike" <[login to unmask email]>@RYCI.COM> on
12/30/99 08:54:34 AM
Please respond to DB2 Data Base Discussion List
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Subject: DB2 Optimizer
Could someone please give me a brief summary of how the
how to choose access paths. We've got some dynamic SQL jobs that
day. One day, they will choose to use the index(es) that we've set
up to be
used and the next day, it uses different ones.