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VSAM Access Interception

 
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Patrick Gantet

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PostPosted: Wed Apr 07, 2010 3:18 pm    Post subject: VSAM Access Interception
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How can I intercept the Write order from a cobol transactional application, in order to stop the write in the file and replace it by a send msg via MQ.
Can I write a component to sustitute the vsam component and install it upper in the DFHRPL card?
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PeterHolland

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PostPosted: Wed Apr 07, 2010 3:57 pm    Post subject:
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As far as i know the DFHRPL contains info about the relocatable program library data sets concatenated to the DFHRPL DDNAME for a CICS system.
So i guess if the vsam component is in the libary list, it can be replaced by a non vsam component.
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dbzTHEdinosauer

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PostPosted: Wed Apr 07, 2010 4:02 pm    Post subject:
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is this change to affect all VSAM files?

where will you obtain the necessary info to populate the MQS API CALL?
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Patrick Gantet

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PostPosted: Wed Apr 07, 2010 5:18 pm    Post subject:
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dbzTHEdinosauer wrote:
is this change to affect all VSAM files?

where will you obtain the necessary info to populate the MQS API CALL?


In fact I have to filter the vsam files : I know the names of the vsam to send to an unix system, and for the others I have to let vsam works normally.
I know the queue and the mecanism to send the records via MQ.
What I need is to understand how to realize and install a filter ontop of the vsam access!

thanks for your help
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Robert Sample

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PostPosted: Wed Apr 07, 2010 5:41 pm    Post subject:
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This would be a an extremely challenging project.
First, I doubt the module is in the DFHRPL -- it is more likely in the STEPLIB (or JOBLIB or link list, depending upon how your site does things). DFHRPL is for application code, typically, not the system code running the applications.

Second, you would be far, far, far better off changing the application rather than attempting to make the kind of global change you're talking about.

Third, you're basically monkeying with some very low level code, so you'd better be writing code that is completely fault-tolerant and very fast or your transactional system may start having major problems.

Fourth, any changes you made would have to be remade (or at least verified) after every application of maintenance to your system. And there's a chance that maintenance will fail due to your added code.

Fifth, any system problems you have will probably have to be resolved on-site since there's no chance IBM is going to even look at any problems until your code has been removed from the system and the problem verified to exist WITHOUT your code.
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CICS Guy

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PostPosted: Wed Apr 07, 2010 6:37 pm    Post subject: Re: VSAM Access Interception
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Patrick Gantet wrote:
How can I intercept the Write order from a cobol transactional application, in order to stop the write in the file and replace it by a send msg via MQ.
If by "transactional" you mean CICS and if by "write" you mean add, then make the file a shared data table and invoke the user exit XDTAD which is invoked for each record that is added to the source data set. You can choose whether to add the record to the data table or not. The CICS Customization Guide should be handy too.
This should be fairly simple....
Quote:
Can I write a component to sustitute the vsam component and install it upper in the DFHRPL card?
An extremely BAD idea......
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Patrick Gantet

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PostPosted: Wed Apr 07, 2010 7:26 pm    Post subject: Re: VSAM Access Interception
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CICS Guy wrote:
Patrick Gantet wrote:
How can I intercept the Write order from a cobol transactional application, in order to stop the write in the file and replace it by a send msg via MQ.
If by "transactional" you mean CICS and if by "write" you mean add, then make the file a shared data table and invoke the user exit XDTAD which is invoked for each record that is added to the source data set. You can choose whether to add the record to the data table or not. The CICS Customization Guide should be handy too.
This should be fairly simple....
Quote:
Can I write a component to sustitute the vsam component and install it upper in the DFHRPL card?
An extremely BAD idea......


thank you very much....
Your solution is fantastic, and compliant with the future change of version of CICS....
Looking at the Guide you indicate, I've seen also the exits XFCREQ and XFCREQC that seems to allow to do what I need. Is it better than XDTAD?

My next step will be to be familiar with ASM to code it! But fot this I've some friends to help me!

best Regards
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CICS Guy

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PostPosted: Wed Apr 07, 2010 7:35 pm    Post subject:
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Quote:
I've seen also the exits XFCREQ and XFCREQC that seems to allow to do what I need. Is it better than XDTAD?
I would tend to lean towards the use of the data table exit (if it can do all I think it can) because there will be no delay or interruption in the servicing of other file control requests, only other data table requests.
I do admit that I have not researched your needs as well as you will, and I realize that some exits do not allow some CICS functionality which you may need. The choice of which exit is yours.
BTW, I have done exits and once you get past their special requirements, they are fairly straight forward. Have fun.... icon_smile.gif
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