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kolusu · Posted: Sun Dec 01, 2002 10:50 pm Post subject: File I/O Mode

Q.I want a sequential File to be opened in the i/o mode and if a condition is matched I will be updating the said sequential file.Can I have a sample code of how to do this task in cobol??

Answer:

GaneshB · Posted: Sat Dec 07, 2002 3:26 pm Post subject:

Kolusu,

Your post is very useful. Thanks for the information. Is it possible to update a record in an ESDS file?
_________________
Regards,
Ganesh.B

kolusu · Posted: Sat Dec 07, 2002 5:45 pm Post subject:

GaneshB,

An ESDS is comparable to a sequential non-VSAM data set in the sense that records are sequenced by the order of their entry in the data set, rather than by key field in the logical record. This could be fixed or variable length records.All new records are placed at the end of the data set. Existing records can never be deleted. If the application wants to delete a record, it must flag that record as inactive. As far as VSAM is concerned, the record is not deleted. It is the responsibility of the application program to identify that record as invalid.

Records can be updated,but without length change. To change the length of a record, you must either store it at the end of the data set as a new record, or override an existing record of the same length that you have flagged as inactive.

A record can be accessed sequentially or directly by its RBA:

Sequential processing: VSAM automatically retrieves records in stored sequence. Sequential processing can be started from the beginning or somewhere in the middle of a data set. If processing is to begin in the middle of a data set, positioning is necessary before sequential processing can be performed.
Direct processing: When a record is loaded or added, VSAM indicates its RBA. To retrieve records directly, you must supply the RBA for the record as a search argument. Although an ESDS does not contain an index component, you can build an alternate index to keep track of these RBAs.Skip sequential processing is not allowed for an ESDS.

Hope this helps...

cheers

kolusu

GaneshB · Posted: Sun Dec 08, 2002 8:59 am Post subject:

Kolusu,

Thanks for the information & quick response.
_________________
Regards,
Ganesh.B

Bechu · Posted: Mon Dec 09, 2002 5:29 am Post subject:

Kolusu,

Excellent piece of information. However I beg to differ on one small point:

Mike Tebb · Posted: Mon Dec 09, 2002 5:58 am Post subject:

Bechu, yes you are quite right that in CICS it is possible to read directly from an ESDS file by using the Relative Bytes Address.

That is not an option in batch COBOL as far as I am aware.
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Cheers - Mike

Manas Biswal · Posted: Mon Dec 09, 2002 6:23 am Post subject:

Hi Bechu, Ravi and Mike
Kolusu is talking about skip sequential processing and not Random Read using RBA. You can very well specify the exact RBA and do a random read from an ESDS in CICS. But I am not too sure about skip sequential processing. In skip seq processing, you basically read records sequentially using STARTBR and READNEXT with the option of skipping some records by directly specifying the key in the RIDFLD parameter. And I am not sure that you can do the same for VSAM ESDS in CICS.
As a matter of fact, I think you cannot also use the GTEQ option(in STARTBR) to position the pointer to the next record after your partial key.
Whatever programs that I have seen using CICS-VSAM ESDS(Not many) first of all move LOW VALUES or HIGH VALUES to the RBA WS field and then issue successive READNEXT or READPREV commands to process records forward or backward sequentially. There is of course a RANDOM READ using RBA which is separate from this.
Please correct me if I am wrong.
Regards,
Manas

Bechu · Posted: Mon Dec 09, 2002 8:24 am Post subject:

Manas,

We too were talking about skip sequential processing and not random read using RBA.

1. Yes, you can use STARTBR and READNEXT with ESDS in CICS, provided you know the RBA.

2. You may be right about the GTEQ option (I have never tried it), but we really don't need GTEQ. If you know the RECL and the record number you are trying to access, RBA can be easily computed and used with STARTBR and EQ itself. (i.e. RBA of first record is 0, LRECL is 100, then you can know that the second record's RBA is 100, third's is 200, tenth's is 900 etc.) I don't see any reason why we'll ever have to do a GTEQ 250 or so! It also does not make sense to use a 'partial key' for an ESDS, which you have mentioned.

Anyway, why worry too much about things that can be easily done with a KSDS? Why force an ESDS to behave like a KSDS? Let us use it for simple functions it is capable of. The others we'll leave to the KSDS.

My question was "Is it right to say skip-sequential processing is not possible on an ESDS?". The answer just happens to be NO (at least, in CICS).

Thanks,
Bechu

Manas Biswal · Posted: Mon Dec 09, 2002 9:12 am Post subject:

Hi Bechu,
Let me make myself a little bit clearer. The following is for KSDS.

Dibakar · Posted: Wed Jan 22, 2003 8:07 am Post subject:

Hi,

Through a single CICS program I want to add a record to a VSAM ESDS and update it a few times. I don't know how to go about it. Can some body help me here, starting from add step.

Thanks,
Dibakar.

kolusu · Posted: Wed Jan 22, 2003 8:46 am Post subject:

Dibakar,

Adding records

Updating records with the READ command

READ Syntax

WRITE Syntax

REWRITE Syntax

Hope this helps...

cheers

kolusu

Dibakar · Posted: Wed Jan 22, 2003 9:37 am Post subject:

It helped.
Thanks,
Dibakar.