Compare VSAM files using DFSORT

pshongal · New User Joined: 14 Jun 2012 Posts: 98 Location: India

Hi,
I have 2 files to be compared each having around 50MM records.

When I do this comparison on flat files, DFSORT takes less time, but when I do this using VSAM files, it takes more time.

I tested in test region with some 400K records (max record length=1450).

Both are variable length files.

Flat file comparison took 0.9 seconds
VSAM file comparison took 9.4 second.

Is there a way I can optimize this?

Nic Clouston · Posted: Thu Nov 23, 2017 4:09 pm

Try using data sets rather than files. And why not try unloading the data sets and comparing the unloads? And those times - are they CPU or wall?

enrico-sorichetti · Posted: Thu Nov 23, 2017 4:19 pm

it is common knowlege that VSAM processing is heavier than PS processing

pshongal · New User Joined: 14 Jun 2012 Posts: 98 Location: India

As Nic mentioned, I have already tried by unloading VSAM and then compare. It works little better but not a huge impact because its double operation as Enrico mentioned

steve-myers · Posted: Thu Nov 23, 2017 6:53 pm

In my opinion, Mr. Sorichetti's first sentence should read, "It is common knowledge that sequential VSAM processing requires more CPU time than an equivalent non-VSAM sequential data set."

In addition, you have to unload each data set (s-l-o-w) before the compare (much quicker). You really haven't gained anything!

enrico-sorichetti · Posted: Thu Nov 23, 2017 7:06 pm

I stand corrected...
if it is the same for You I would prefer to sit corrected, it is more comfortable