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Bill
You should take a look at site <http://www.iseries.ibm.com/db2/sqe.html>,
which also has a link to an APAR that gives you the latest changes.
According to the APAR, "join queries and queries with IN or OR predicates
are now able
to run with the SQL Query Engine".
BTW, it's not just the optimizer that is affected - the engine is
completely different, running in SLIC. The optimizer actually runs above
the MI layer and determines whether a statement qualifies for the new
engine. So parsing is still done above MI, in XPF. Optimization may be
slower, as it is now a 2-layer process. But that is often not an issue in a
long-running statement - better optimization often results in shorter
overall runtime.
Original plans called for support of complex (that means messy joins)
read-only statements. But it is being rolled out slowly - the APAR tells
you what is currently supported.
Another piece of this is new statistics on individual columns - things like
cardinality (number of distinct values), and distribution stats (histogram
and most frequent values). These can assist the optimizer by giving it more
exact data, instead of the optimizer making guesses, based on the nature of
the statement, as the "classic" one does. I.e., estimates of the number of
records in the returned recordset can be closer to reality. OpsNav has
tools for viewing thse stats, and there is a set of tools at the
above-listed site for looking at these things from a green-screen
BTW, the design of the new engine is quite cool - allows plugging in new
function quite easily - very object-oriented.
HTH
Vern
At 01:17 PM 8/18/2003 -0500, you wrote:
One of the things listed in "What's new in V5R2" is a rewrite of the query
optimizer to improve SQL / query performance. We are upgrading soon, but
being asked now about things we can do to aid in CPU usage and user
experience. For those of you that have already gone to V5R2, has there been
a noticeable performance improvement? Our apps are VERY SQL intensive to
accommodate completely dynamic sorting and filtering, and while our system
performance is good (box and index tuning done and reviewed regularly) we
are always prodded by our hardware guys to see if we can't get a few more
RPMs out of the hamster wheel.
Any shared experience would certainly be appreciated.
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