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Han Solo
Beginner
Joined: 20 Jan 2005
Posts: 2
Topics: 1
Location: Spain
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 Posted: Mon Oct 03, 2005 5:09 am Post subject: Optimal Characteristics of load Libraries |
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Is there some recomendation about the characteristics that must have the libraries with executable modules ( from a perfromance point of view)?.
If exist, Where can i find references to this question ?
Thank you in Advance. |
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kolusu
Site Admin
Joined: 26 Nov 2002
Posts: 12376
Topics: 75
Location: San Jose
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| Posted: Mon Oct 03, 2005 8:06 am Post subject: |
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Han Solo,
A typical Load library will have the following attributes. Allocate the PDS with approriate space parameters.
| Code: |
Organization . . . : PO
Record format . . . : U
Record length . . . : 0
Block size . . . . : 19069
Data set name type : PDS
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The load library may be in the system linklist, or it may be in library lookaside (LLA), or it may be in virtual lookaside facility (VLF). It may additionally be APF (authorized program facility) authorized.
A load library in LLA has its directory stored in memory, for faster access. If your program is written to a library in LLA and you subsequently update the program, you must ensure that the in-memory copy of the directory is refreshed from the disk copy, otherwise the system will not be able to successfully load and run your program. LLA can identify the most frequently used modules in a library and store them in VLF (basically a set of data spaces), to speed up program fetch and load times. A program generation that uses the link-edit option AC=1, and writes the module to an APF authorized library, results in what is called an APF authorized program. This program may run in a system storage protection key or in Supervisor state.
Hope this helps...
Cheers
Kolusu
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Kolusu
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Phantom
Data Mgmt Moderator
Joined: 07 Jan 2003
Posts: 1056
Topics: 91
Location: The Blue Planet
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| Posted: Mon Oct 03, 2005 8:11 am Post subject: |
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Wow....Never ever thought that there would be so many options with a load library... 
Thanks so much Kolusu,
Regards,
Phantom |
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Han Solo
Beginner
Joined: 20 Jan 2005
Posts: 2
Topics: 1
Location: Spain
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| Posted: Mon Oct 03, 2005 11:01 am Post subject: |
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Ok, I'll describe the entire problem that makes myself ask such a question. We have discovered that we have equivalent libraries with load modules with different BLKSIZE
(more precise; library A with BLKSIZE 32760,library B with BLKSIZE 28000). We don |
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semigeezer
Supermod
Joined: 03 Jan 2003
Posts: 1014
Topics: 13
Location: Atlantis
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| Posted: Mon Oct 03, 2005 2:08 pm Post subject: |
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Best block size for load modules is 32760 in all cases. This is not true of any other type of library. I don't recall why that is true, but it has been IBM's recommendation for several years. This is the one case where 1/2 track blocking is not the best way to go. I suspect that program load functions are able to take advantage of some of the hardware idiosyncracies to allow very fast access (chained CCWs or something maybe). And the loader/binder can write data to the tracks so space is not wasted.
Also, for security reasons, you can't mix APF and non-APF libraries in a concatenation and use the authorization. Any one non-APF library in a concatenation makes the whole concatenation unauthorized. |
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