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EXCP and SERV in JES2 job log

 
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Jeya Raj

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Joined: 14 Jan 2007
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PostPosted: Wed Mar 19, 2014 2:37 am    Post subject: EXCP and SERV in JES2 job log
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Hi,

I'm trying to learn more about EXCP and SERV in JES2 job log. I hope EXCP is the count of read and write of records. I tried to get more info, but couldn't find the simple explanation.

What do they mean in a job stat?

Does EXCP and SERV count increase when the program tries to write records in a unopened file? or When a program goes into loop , do the count increase?. I really appriciate any help on this topic.

Thank you.
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Terry Heinze

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PostPosted: Wed Mar 19, 2014 2:52 am    Post subject:
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(EX)ecute (C)hannel (P)rogram counts are basically I/Os (reads and writes). (S)tart (IO)s are EXCPs per second. You might find more info at http://pic.dhe.ibm.com/infocenter/zos/v1r12/index.jsp?topic=%2Fcom.ibm.zos.r12.hasa300%2Fj2log.htm
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Rohit Umarjikar

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PostPosted: Wed Mar 19, 2014 2:53 am    Post subject:
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EXCP:

A count of the number of blocks of data transferred. The EXCP is an I/O subsystem driver. To request the movement of data, either the access method or the user program presents information about the operation to the EXCP processor by issuing the EXCP macro instruction. EXCP translates this information into a format understandable to the channel subsystem and invokes the I/O supervisor (IOS).

SMF maintains counts of these EXCP requests. An EXCP count is a block of data transferred. However, both a 16-byte block and a 32756-byte block count as one EXCP. Also, the I/O access method or I/O driver must count blocks transferred and pass that count to the SMF count routine.

You can get more here,

http://publib.boulder.ibm.com/tividd/td/perfrpt/SH19-6818-05/en_US/HTML/drlm9m58.htm

Also you can find more on SERV and EXCP here too,

http://pic.dhe.ibm.com/infocenter/zos/v1r12/index.jsp?topic=%2Fcom.ibm.zos.r12.hasa300%2Fj2log.htm
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Robert Sample

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PostPosted: Wed Mar 19, 2014 3:53 am    Post subject:
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EXCP are related to the count of records read and written, but are not -- as explained elsewhere -- directly translatable to the number of records read / written. Service units are a measure of the work done by the system.

When a program goes into a loop, whether the EXCP count increases depends upon what is in the loop (no read or write statements, no EXCP are done); the service units will increase in a loop since the system is doing work.
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don.leahy

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Location: Whitby, ON, Canada

PostPosted: Wed Mar 19, 2014 5:47 pm    Post subject:
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Terry Heinze wrote:
(EX)ecute (C)hannel (P)rogram counts are basically I/Os (reads and writes). (S)tart (IO)s are EXCPs per second. You might find more info at http://pic.dhe.ibm.com/infocenter/zos/v1r12/index.jsp?topic=%2Fcom.ibm.zos.r12.hasa300%2Fj2log.htm

A co-worker once came to me for help because he thought his job was running too slow and thought it might be due to a large number of "Exception counts". I had no idea what he was talking about so I told him to take another look at his program and tell me what kind of exception conditions it was expecting. His eventual response made no sense, so I asked him to show me how he knew that the "exception count" was excessive. I nearly fell out of my chair laughing when he pointed to the EXCP count in his joblog. icon_lol.gif
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dick scherrer

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PostPosted: Wed Mar 19, 2014 6:46 pm    Post subject:
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Yup, as recently as last week someone here (client) referred to EXCP as "exception count". That is what they were told many years ago (20+) and most have never been "out in the real world" so they don't know any better.

They do understand that this is a measure of i/o . . .
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Jeya Raj

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PostPosted: Thu Mar 20, 2014 7:43 am    Post subject:
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Thank you so much for you replies.

I never checked EXCP and SERV before when I ran the jobs( I do mainly CICS programming). All I check was the CPU and elapsed time. Now I have an issue and I need to find out about the EXCP counts.

Here is my issue scenario:

I ran a job in TEST and PROD with SAME input file.
Here is my job model:

//JOB1234 JOB (1234),CLASS=’A’
//STEP01 EXEC PGM=MTPBATCH --> close OUTFILE E.F.G
//STEP02 EXEC PGM=PROGRAM1
//INFILE DD DSN=A.B.C, DISP=SHR --> has about 290K records in it
//OUTFILE DD DSN=E.F.G,DISP=OLD
//*

In TEST, the job ran ok and the timing was normal. But when I ran the same job in PROD, it had an issue.

On STEP01, the file was not closed(IEF099I JOB JOB1234 WAITING FOR DATA SETS) and STEP02 was waiting for the OUTFILE dataset. After 10 mins of CPU time, I killed the job. When I checked the JES2 Log, I saw the EXCP count as 30000k and SERV as 43454K. Below are the STAT from both the TEST and PROD

In TEST run the EXCP and SERV count as below
The test run had 833K EXCP and 13768K SERV
CPU time 3.23 mins

In PROD run when the job was killed the EXCP and SERV count as below
The PROD run had 30298K EXCP and 43488K SERV
CPU time 10.53 mins

My questions are :
1. Why the EXCP count was so high when I ran the same job in PROD when it didn’t write any records into the OUTFILE? (Hope read count won’t be that much since the INPUT file is same in both TEST and PROD)

2. How important is EXCP count while running a job?

3. Does CPU time play a role in EXCP count?

Appreciate your help.

PS: The job ran fine in previous runs. Sorry for the lengthy post...

Thank you.
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steve-myers

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PostPosted: Thu Mar 20, 2014 10:57 am    Post subject:
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  1. The EXCP term refers to the OS/360 macro used to initiate an I/O. Most of the time one EXCP is equivalent to one physical record, but clever programming can read or write several physical records with one EXCP macro. Since you refer to something reported in the JES job log, the data presumably was extracted from an SMF type 30 record, probably by the IEFACTRT user exit. Without the the SMF data, and possibly the code for the exit routine, it is impossible to validate the numbers.
  2. EXCP count can be quite important.
    • EXCP uses a surprising amount of CPU time to prepare the system to do your I/O.
    • The elapsed time to perform the I/O can be quite long. This has been discussed elsewhere in this forum.
  3. As I mentioned before, EXCP can be more CPU intensive than one might expect, and every EXCP usually results in execution of a WAIT macro to pause execution until the I/O completes. In other words, more CPU usage.
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Rohit Umarjikar

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PostPosted: Thu Mar 20, 2014 11:59 am    Post subject:
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Jeya,

It is appreciated that you are showing interest to learn more and more and hence I thought of getting additional information ( as there is no one liner answers to what you HAVE ASKED) which would answer all of your questions in detailed way along with the above expert's comments,

1) http://pic.dhe.ibm.com/infocenter/zos/v1r12/index.jsp?topic=%2Fcom.ibm.zos.r12.icet100%2Fpind.htm
2) http://www.ibmmainframes.com/about28408.html
3) http://ibmmainframes.com/about51365.html
4) http://web.utk.edu/~mnewman/ibmguide10.html
5) https://www.ibm.com/developerworks/community/blogs/MartinPacker/entry/it_depends_smf_30_job_timings_and_cpu_time1?lang=en

Once you go throught all of them you would endup understanding how this works..
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Jeya Raj

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PostPosted: Mon Mar 24, 2014 11:11 pm    Post subject:
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Thanks Rohit for the extra info. The info was very helpful.

Regards,
Jeyaraj
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Pete Wilson

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PostPosted: Thu Mar 27, 2014 2:30 pm    Post subject:
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You didn't say if this was a VSAM file or not, but if it is, you say at one point the file wasn't closed, so perhaps it had to do an implicit verify when you opened it for output. The verify reads the file sequentially in this case to find the correct high use RBA so would increase the EXCP count.
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