Re:QSAM or PREFETCH - pros and cons

Discussion created by ca.portal.admin on Feb 7, 2008
Hi gang,

Your posts on the topic ""Local mode update and fastaccess"" leads me to
another question:

When to use IDMSQSAM vs. when to use PREFETCH.

I've used both in a limited way, and years ago, at another company,
switched to PREFETCH because QSAM didn't seem to do much for me while
PREFETCH did (after it came out.)

Lutz's comment that QSAM only works on one file (the first file in a
multi-file area?) kind of strikes me as why I wasn't overly impressed
like most of you are with QSAM.

In this shop, we have numerous huge areas (95% of all areas are 1
rec/area) and a home-grown program that unloads records via full track
reads. As a result, the only place QSAM is used is in UNLOAD/RELOAD


Richard Pierce
(617) 973-8911

Remember, the answer to all questions is a reply, but a reply is not
necessarily an answer.
IDMS Public Discussion Forum


Re: Update on Local Mode Update Job
"Ah, yes, the big buffer issue. I seem to remember that being a problem
a long time ago when I help improve a customer's order processing system
(that was back in 1989-90!). The DBA there seemed to think that a busy
database was a happy database and had 24k DB pages and 32k buffers.

As for the sorted chain sets, I would be willing to bet that they are a
big part of the problem. Again, back in 1990 for another client, I
converted their sorted sets to user indices and the performance
improvement was dramatic! They had a particularly crazy setup with
calc-to-calc sorted sets in the same area with an average member count
of 20,000 (and some of them went into 6-figures!) And they wondered why
their I/O counts were off the charts! That was a I could be a hero
rather easily. Now I'm struggling with SAP, Oracle, and most difficult
of all--end users!

Good luck, Bill with your prod run.

Dan Miley
Lockheed Martin