Find the size of a PS file before reading

Vishnupriyamr · New User Joined: 06 Jul 2023 Posts: 3 Location: India

Hi Everyone

I am looking to find the size of a PS file with variable records that are assigned by the user .

The user will create the PS file with certain cylinders and block size. We need to write variable records to that block size. We want to ensure that we don't blow up the file. So we want to calculate before hand, how much data (bytes of data) it can hold and put a check.

So from the cobol program, is there a way to find the configuration of the file or the size of the file ?

Please give some thoughts.

Thank you !

sergeyken · Posted: Thu Jul 06, 2023 8:09 pm

There is no way to do this. Neither in COBOL, nor anywhere else.

BTW, what “blowing up the file” stands for??

PS.
The “file” in mainframe is equivalent to “DDNAME”. It has no size at all. It is something similar to a sort of connecting pipe, for data to flow between a program, and a dataset.

sergeyken · Posted: Thu Jul 06, 2023 8:31 pm

One more note.
You want “to find the size of a PS dataset (not file!) before READING it”, just to start WRITE to it - ???!!!
What does this mean??

sergeyken · Posted: Thu Jul 06, 2023 8:53 pm

Highly likely, you want to find in advance: how much data might fit into a pre-allocated dataset, correct?

Absolutely not clear, what you plan to do if your data would not fit?

Normally it should be done in opposite way: FIRST calculate the expected amount of data to be written, and THEN allocate the dataset with required size. You can also use:
- dynamic allocation tools,
- secondary allocation amount,
- multi-volume allocation feature,
- etc.

Initially you tried to resolve your issue from the end. Better try to resolve it from the beginning.

Robert Sample · Posted: Thu Jul 06, 2023 9:49 pm

sergeyken · Posted: Fri Jul 07, 2023 12:41 am

There is no one word about any issue, or any question about the record size. The TS is interested in “file size”, and refuses to clarify any details, at all.

Vishnupriyamr · New User Joined: 06 Jul 2023 Posts: 3 Location: India

Thank you Rob and Sergey for your replies. I apologize for the late reply . As I am in a different time zone, I just saw your replies now.

In our case, we supply the JCL to the user so the user can assign the PS dataset that they have created, to the DDNAME.

The record length we are assigning is 32100 for the file. But the user will create the PS dataset with Cylinders/Tracks. So we want to find out how many records that particular dataset can hold. So I am trying to see , if there is a way to find the allocations done by the user for the PS dataset.

Are there any utilities that we can call to find the allocation of the PS dataset ?

In our case, we want to continuously write the data to the PS dataset and once it is full ,we want to switch to another dataset to continue writing the data there.

I used " blowing up" for the scenario when the PS dataset is full and throwing error.

Please let me know your thoughts on this and sorry for any confusion.

Thank you !

Pete Wilson · Posted: Fri Jul 07, 2023 8:53 pm

The information you're providing is almost impossible to interpret because it's so incoherent.

It looks like the Users are provided JCL by you, and this 'allocates' (not assign) the dataset as RECFM=VB,LRECL=31000 bytes using the 'DDNAME' you have chosen to use. And the User's have the option to specify SPACE values for the datasets on the DDNAME based on their expectations of the maximum number of records to be written to the dataset? Is that correct?

Specifying SPACE in terms of TRK/CYL is quite primitive really unless you know the geometry of the disk device. Currently a 3390 TRK is 56664 bytes, and there's 15 TRKs to a CYL.

But you can allocate space according to the number of expected records instead which means you don't need awareness of TRK/CYL capacities.
e.g.
SPACE=(31000,(50,50),RLSE),AVGREC=M
This will initially request enough Primary space for 50 million records of 31000 bytes, and same for Secondary space.

BUT, depending on the DATACLAS that gets assigned by SMS to the dataset it could potentially hold a LOT more than that because:
a) DATACLAS may allow it to extend to multiple volumes
b) DATACLAS may make it Extended Format so can have up to 123 extents per volume with no size limit for the total extents. (Non Extended is limited to 65k cyls per volume and max 16 extents)
c) DATACLAS may provide Compression of the data so uses less of the allocated capacity.

I'd suggest you talk to whoever does your Storage admin at your company and I'm sure they'll be able to provide more specific advice than this forum can because so much is site dependent. There may even be a DATACLAS that will provide the space without you having to code it, so you can code DATACLAS=name instead. And potentially a DATACLAS can be automatically assigned to a dataset by SMS without having to code it in the JCL at all.

sergeyken · Posted: Fri Jul 07, 2023 10:34 pm

You can specify the requested size in blocks:

Joerg.Findeisen · Posted: Fri Jul 07, 2023 11:49 pm

I would also recommend to work with multivolume. A static volcount (coding VOL=(,,,<n>)) might work, but will stress your catalog structure. DYNVOL is the way to go here regarding definitions in DFSMS.
Sometimes "less" is "more" does not only apply to UNIX, see how you can deal with number of extents and such. DFSMS offers a wide range of possibilities for "flat" datasets. Basically you can cover everything with small efforts (One Ring to rule them all).

don.leahy · Posted: Sun Jul 09, 2023 1:58 am

don.leahy · Posted: Sun Jul 09, 2023 1:59 am

Vishnupriyamr · New User Joined: 06 Jul 2023 Posts: 3 Location: India

Thank you all for the suggestions.

I was able to find a way to get this working. In the cobol program, used the DSINFO DATASET(DSNAME) command to get the allocation values. All the values will be in the Z variables. Then used the VCOPY command to retrieve the Z variables in the working storage variables of the program and used them in the program.

STRING "DSINFO DATASET('DSNAME')"
DELIMITED BY SIZE
INTO CMD-TEXT.
MOVE 44 TO CMD-LENGTH.
CALL 'ISPEXEC' USING CMD-LENGTH, CMD-TEXT.

CALL 'ISPLINK' USING WS-V-COPY
WS-ZDSORG
WS-8
V-ZDSORG
WS-MOVE.

working storage variables
05 V-ZDSORG PIC X(08) VALUE SPACES.
05 WS-ZDSORG PIC X(8) VALUE 'ZDSORG '.
05 WS-MOVE PIC X(8) VALUE 'MOVE '.
05 WS-8 PIC S9(7) COMP VALUE +8.

sergeyken · Posted: Tue Jul 11, 2023 5:38 pm

Please, learn this very primitive trick, to make your posts more attractive to readers: