Re: Batch Billing Performance.

[fkolmann@xxxxxxxxxxxxx]

pgreenfi@ssax.com wrote:

> Reply to fkolmann@revlon.com.au:
>
> Not only does the optimizer take into consideration the number of records
> in your file, but it also looks at the data skew, and data key skew.  The
> data is only one part of the equation.  The optimizer also looks at the
> hardware configuration, specifically the memory and the number of disk arms
> available.
>
> Obviously all of these factors, and OS/400 level/PTF levels, can be very
> different from implementation to implementation, and therefore an index
> which may be good for one environment may have no effect or even be
> detrimental to another site.
>
> For more details on the workings of DB2/400 see the DB2 Programmers Guide,
> in particular check out Appendix D for information regarding DBMON.
>
> Regards,
> Peter Greenfield

Thanks for the info Peter, I have read and tried to understand (tried is the
operative word here)
the DB2 programmers guide, I think it was you who sent it to me over the net,
much appreciated.
I have since got many other IBM manuals downloaded (Adobe Acrobat is a wonder)
but back to the
optimiser.

The point that creating a lgl can be detrimental I cannot understand.
What this means to me is that the optimiser makes a mistake.
Given a certain set of PTFs and data records one can create a lgl file in an
attempt to help SQL
and the optimiser the uses the lgl file in preference to one of the other
esoteric access methods
(usually forms of block reads) and then slows the performance of the process.
If the optimiser cannot correctly choose the fastest processing method given
that I have helped it
by creating and index then we have no hope.

We are for the most part big boys now and our hardware configs are usually the
first thing that is checked
and most people have done the rigth thing and parted with copious amounts of
cash to upgrade the
hardware so hardware is as good as its going to get , its now up to the
software.


PS.  Nothing about this whole question is 'Obvious' to me.

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