ca.portal.admin

Re: COBOL calls

Discussion created by ca.portal.admin on Sep 30, 2007
Jon, let's look at it some more. An svc screen is telling the operating
system first level interrupt handler to give your routine (the svc screen)
control on every svc call. An svc call is an operating instruction that
causes a machine iterrupt. So of course not every user program can do that,
because if IBM allowed it, then any user could highjack the operating system
by interrupting calls for operating system services. But I dont think
setting the svc screen in and of itself is that performance degrading, but
letting a cobol application program make an svc call is. Depending on the
transaction rate, this could be expensive. Each time that Cobol program
does an svc call, like a getmain, there's a machine interrupt, the machine
gives control to the first level interrupt handler in MVS and looks at the
call, examines whether it's one that is being screened, then loads the
routine if it screens this svc, and gives control back to the MVS
dispatcher, which may or may not dispatch IDMS for continuation, depending
on the priorities in the system. Part of IDMS's great performance is due to
the pains that developers went through to keep extraneous svc calls to a
minimum. So, I think the bottom line is, the setting of the screen isn't
prohibitive, but letting a cobol program make the svc calls is. Of course
that wouldn't be IDMS's fault, since it's a COBOL compile option and a
matter between the user and IBM.



Lutz Petzold




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Re: COBOL calls
"Jon, let's look at it some more. An svc screen is telling the operating system first level interrupt handler to give your routine (the svc screen) control on every svc call. An svc call is an operating instruction that causes a machine iterrupt. So of course not every user program can do that, because if IBM allowed it, then any user could highjack the operating system by interrupting calls for operating system services. But I dont think setting the svc screen in and of itself is that performance degrading, but letting a cobol application program make an svc call is. Depending on the transaction rate, this could be expensive. Each time that Cobol program does an svc call, like a getmain, there's a machine interrupt, the machine gives control to the first level interrupt handler in MVS and looks at the call, examines whether it's one that is being screened, then loads the routine if it screens this svc, and gives control back to the MVS dispatcher, which may or may not dispatch IDMS for continuation, depending on the priorities in the system. Part of IDMS's great performance is due to the pains that developers went through to keep extraneous svc calls to a minimum. So, I think the bottom line is, the setting of the screen isn't prohibitive, but letting a cobol program make the svc calls is. Of course that wouldn't be IDMS's fault, since it's a COBOL compile option and a matter between the user and IBM.



Lutz Petzold




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you think you have received this e-mail in error, please advise the
sender by reply e-mail and then delete this e-mail immediately.
Thank you. Aetna
"
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Re: COBOL calls
"Lutz -

This is very interesting....
This is the first time I've ever heard that SVC screening is an SVC call in
itself.
I thought the whole purpose was to prevent SVC calls for functions that
could be performed most efficiently using IDMS-DC services.
I had always thought it was a ""trap"" before the SVC was allowed to take
place.
This sounds self-defeating.....you make an SVC call to prevent making an SVC
call.
Can you share more information on this?

Thanks.
Jon Gocher

----- Original Message -----
From: ""Petzold, Lutz"" <PetzoldL@AETNA.COM>
To: <IDMS-L@LISTSERV.IUASSN.COM>
Sent: Thursday, September 27, 2007 9:55 AM
Subject: Re: COBOL calls


Yes, that's the way it works, although at one time svc screening was
turned off I thought, but you do realize that an svc screen is an svc
call in itself, and puts the IDMS region in an interrupt state, meaning
there is a severe performance penalty on applications that do a lot of
'calls'. I never heard CA promoting operating system waits/interrupts.


Lutz Petzold

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