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How to get last RRN in the RRDS file?

 
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rajesh_mbt

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PostPosted: Fri Aug 12, 2011 6:00 pm    Post subject: How to get last RRN in the RRDS file?
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I want to retrieve last RRN from a RRDS file, i tried move -1 to the value of RIDFIELD in the STARTBR statement. But it is not giving the correct RRN while reading the file thru READPREV.

05 WS-LAST-RRN PIC S9(8) COMP.
MOVE -1 To WS-LAST-RRN

Please help me to get to the last RRN of the record.
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Bill Woodger

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PostPosted: Fri Aug 12, 2011 6:09 pm    Post subject: Reply to: How to get last RRN in the RRDS file?
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Why do you want this?

If the RRDS behaves like other types of VSAM, there isn't really a last number. If you add records, serially, and the dataset gets another extent, the "last number" changes. I've used RRDS's, for a dateset with widely varying numbers of records. Can't say I actually know that multiple extents were used, but I'd be surprised if not.
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Robert Sample

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PostPosted: Fri Aug 12, 2011 6:28 pm    Post subject:
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But it is not giving the correct RRN while reading the file thru READPREV.
What does it give you? What would be the CORRECT RRN as opposed to what you are getting?
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Bill O'Boyle

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PostPosted: Fri Aug 12, 2011 6:36 pm    Post subject: Reply to: How to get last RRN in the RRDS file?
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Perhaps the file needs to closed/opened (catalog update) beforehand to obtain the last RRN as this is a requirement to obtain the last RBA in an ESDS file.

Bill
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rajesh_mbt

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PostPosted: Fri Aug 12, 2011 7:14 pm    Post subject: Reply to: How to get last RRN in the RRDS file?
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Thanks for all your swift response. This file is being updated by some other program, am just want to read it from my program.
Let assume, the file is updated and contains 100 records. I want to read backward from 100th record.

In order to do so, I should get 100 as the last RRN number.
My question is how do point/get the the last record(which is 100) on the file.
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Robert Sample

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PostPosted: Fri Aug 12, 2011 7:25 pm    Post subject:
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Let assume, the file is updated and contains 100 records.
I don't know if you are being deliberately obtuse, or if you just don't understand RRDS.

Assuming you are dealing with a fixed-length RRDS (since variable length RRDS would make what you want to do pretty much impossible any way) -- an RRDS contains a fixed number of "slots" for records -- the number is set by the record size and the number of tracks / cylinders / etc allocated to the RRDS. Those "slots" may contain data or they may be empty -- but they ALWAYS exist.

So when you say "contains 100 records", do you mean:
1. the RRDS was allocated with 100 slots?
2. the RRDS was allocated with an unknown number of slots and the first 100 have data?
3. the RRDS was allocated with an unknown number of slots and there are 100 slots that are not empty scattered through the entire file -- which is quite possible?
4. something else entirely that you have not yet explained?
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rajesh_mbt

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PostPosted: Fri Aug 12, 2011 7:26 pm    Post subject:
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Robert Sample wrote:
Quote:
But it is not giving the correct RRN while reading the file thru READPREV.
What does it give you? What would be the CORRECT RRN as opposed to what you are getting?

I am getting constanly a same number though file is being added the records with next sequence RRN icon_sad.gif .
I am not sure how is it possible to get same RRN as last record!!!
Is my move statement -1 to RIDFIELD correct? I am thinking this should be something else to point last record. icon_confused.gif
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Robert Sample

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PostPosted: Fri Aug 12, 2011 7:32 pm    Post subject:
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I am not sure how is it possible to get same RRN as last record!!!
Okay, so you do NOT know how RRDS works. Records added to an RRDS MUST fit into one of the existing slots. You are getting back the same RRN for the last record because the last record number will not change -- an RRDS file will not extend itself like ESDS or KSDS when records are "added", since the file must be pre-allocated with a given number of slots.

The manual states using -1 for RIDFLD will return the last slot number -- but again, that will be a fixed value that does not change until the file is deleted and redefined with a different number of tracks or cylinders in it. You cannot use the last RRN of an RRDS file to find the last record "added" since that will depend upon which slot the record was placed in.
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rajesh_mbt

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PostPosted: Fri Aug 12, 2011 7:35 pm    Post subject:
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Robert Sample wrote:
Quote:
Let assume, the file is updated and contains 100 records.
I don't know if you are being deliberately obtuse, or if you just don't understand RRDS.

Assuming you are dealing with a fixed-length RRDS (since variable length RRDS would make what you want to do pretty much impossible any way) -- an RRDS contains a fixed number of "slots" for records -- the number is set by the record size and the number of tracks / cylinders / etc allocated to the RRDS. Those "slots" may contain data or they may be empty -- but they ALWAYS exist.

So when you say "contains 100 records", do you mean:
1. the RRDS was allocated with 100 slots?
2. the RRDS was allocated with an unknown number of slots and the first 100 have data?
3. the RRDS was allocated with an unknown number of slots and there are 100 slots that are not empty scattered through the entire file -- which is quite possible?
4. something else entirely that you have not yet explained?


That 100 records i mentioned for an example. The file is already running for many years, so i've no idea on it. Also, I am not sure why you took that much complicated.
In general, how do you achiecve to get last RRN? Thanks for your response..
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rajesh_mbt

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PostPosted: Fri Aug 12, 2011 7:37 pm    Post subject:
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Robert Sample wrote:
Quote:
I am not sure how is it possible to get same RRN as last record!!!
Okay, so you do NOT know how RRDS works. Records added to an RRDS MUST fit into one of the existing slots. You are getting back the same RRN for the last record because the last record number will not change -- an RRDS file will not extend itself like ESDS or KSDS when records are "added", since the file must be pre-allocated with a given number of slots.

The manual states using -1 for RIDFLD will return the last slot number -- but again, that will be a fixed value that does not change until the file is deleted and redefined with a different number of tracks or cylinders in it. You cannot use the last RRN of an RRDS file to find the last record "added" since that will depend upon which slot the record was placed in.


Thanks Robert for your reply. Actully, am not familiar with RRDS thats why got confused.
Let me check at my end here too
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Robert Sample

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PostPosted: Fri Aug 12, 2011 7:43 pm    Post subject:
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I took the time to explain all that because your problem is NOT how to get the last record of an RRDS in CICS -- that's easy; move -1 to the RIDFLD and do the READ. However, that record is NOT what you are wanting; you want the last updated record and that is a very big can of worms -- depending upon how the file is set up and used, the FIRST record (RRN zero) could have been updated last.

Without more information, and a LOT more understanding of RRDS files and the application on your part, what you are wanting cannot be done -- at least based on what you've given us so far.
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dbzTHEdinosauer

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PostPosted: Fri Aug 12, 2011 7:50 pm    Post subject:
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we always had a simplistic approach to rrds files.
the first slot always contained a field, the value of which was the next available.

no one can 'just add records to a rrds' without sometype of control.

as the TS said, "he don't know nothing".

this is a site specific thing, and should be handled by the TS asking someone there!
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Robert Sample

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PostPosted: Fri Aug 12, 2011 7:55 pm    Post subject:
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Dick -- actually, this is not even a site-specific issue; it is an issue specific to that particular application at that site. I've known applications to use the first slot for control data, and I've known applications using the LAST slot for control data. But, as you said, records are not "added" to an RRDS -- a given slot is updated either from empty to containing data, or from containing data to containing other data.
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