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Peformace issues for UNIT=(SYSDA,2) with huge CYL


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alan_blore

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Joined: 01 Aug 2007
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PostPosted: Fri Apr 16, 2010 9:48 pm
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Hi,

I have JCL which creates a PS file defined with

UNIT=(SYSDA,2),SPACE=(CYL,(600,100),RLSE),

Now, I have doubt here - since this step executes for hours.

By coding SYSDA,2 for UNIT - does it mean we are searching for CYL,(600,100) within two volumes?

By increasing the UNIT to SYSDA,14 - Will it make any difference?

Thanks!
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Robert Sample

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PostPosted: Fri Apr 16, 2010 10:43 pm
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The fact that the step executes for hours is almost certainly not related to the space request. Considering DASD access times are in milliseconds, the space is either acquired or not acquired in a fraction of a second. If not acquired, your job will get an x37 abend.
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PeD

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Joined: 26 Nov 2005
Posts: 459
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PostPosted: Sat Apr 17, 2010 12:19 am
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Quote:
By increasing the UNIT to SYSDA,14 - Will it make any difference?

We can discuss on that, but not significantly.

But .... which language? how many records? blocksize? buffersize?....

Check all that.
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dick scherrer

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Joined: 23 Nov 2006
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PostPosted: Sat Apr 17, 2010 1:02 am
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Hello,

Quote:
Now, I have doubt here - since this step executes for hours.
Allowing the allocation to span more volumes will not significantly alter this. . .

The 2 things to consider are the volume of data and how the code is written. Code that runs sub-second for 100 records may fail when full volume data is processed (which is why it is very risky to promote code that has not gone thru a "full volume" test before promotion to Production).

How many records are to be read? Written? Will any of the records be accessed multiple times? Is the input on tape/cart? If so, how long is the wait between mounts?

Posting the full jcl for this step may help someone help you.
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alan_blore

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PostPosted: Tue May 18, 2010 6:29 pm
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Thanks All for Info...and sorry for late reply
It was the CPU which was full, so making this job to run long. Now it is ok.

But now the other question arises...

Consider this step - a SORT or a program - whatever it is -

What would be ideal value for 'n' in parameter UNIT=(SYSDA,n)?

I believe we can check with storage team for this, but that is tough for me in a day to day scenario, If I need to decide - what should I do..
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dick scherrer

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PostPosted: Tue May 18, 2010 7:12 pm
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Hello,

Just because something is a bit of effort does not mean it should not be done. . . Your storage management people should be your first place to ask. They manage your system and know particulars - we do not.

There is no "ideal value". It is not as though the dataset will be scattered about thus improving performance. . . Suggest you look in the JCL Language Reference (link to "IBM Manuals" at the top of the page) and learn about the UNIT subparameters.
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