KSDS VSAM define tune

rally · New User Joined: 28 Jul 2005 Posts: 37

Hi,

I have a large VSAM file need reorg, below is some info for it:

1. there are many CA/CI split during online.

2. the reason to create the CA/CI is most of the new records(50%)
will be insert into last part of the file, and other 50% records will be
added to the whole file randomly.

Any idear regarding above case?

How can I overcome the CA/CI splits issue,
this make the our online transaction process came to very slow.

From normally 4 txns/second down to 1 txn/5 seconds.

Thanks.

William Thompson · Posted: Sun Feb 11, 2007 3:19 pm

Without good information, it is going to be hard.
The 50% at the rear should take care if itself but the random adds need to be addressed. The CI splits are minor, it is the CA splits that cost. What is the current CI and CA freespace? How often is the file reorged? What is the current CI and CA size?
My approach would be to start with a large CA size (full cylinder), a slightly larger than normal CI size and, maybe, 25% freespace in both and do a listcat every day looking for splits. At this point, CI splits are good and a small count of CA splits aren't too bad - while a CA split is expensive to run time, once done there is a lot of freespace now available. Keep watching and adjusting the freespace each time you reorg and you can find an optimum percentages for both CI and CA.

Bitneuker · Posted: Mon Feb 12, 2007 7:06 pm

Also consider the index and not just data.

William Thompson · Posted: Mon Feb 12, 2007 7:15 pm

IIRC, lately a lot of the tune-ability for indexes has been removed in favor of AMS deciding on its own. But you are right, you could really screw performance by undersizing index CIs......

Bitneuker · Posted: Mon Feb 12, 2007 7:18 pm