Order of dataset in dataset concatenation



JES, JES2, JCL utilities, IDCAMS, Compile & Run JCLs, PROCs etc...

Order of dataset in dataset concatenation

Postby nikesh_rai » Tue Oct 08, 2013 11:36 pm

Hi Guys,

While concatenating datasets having same record length and different block size, is it must to keep the dataset with largest block size at first.
I have tested this keeping dataset with largest block size at the last and not getting any error. I saw many posts where it was saying it is must to keep largest block size at first. Please suggest.
Thanks
Nikesh Rai
nikesh_rai
 
Posts: 192
Joined: Tue Oct 18, 2011 1:27 am
Has thanked: 17 times
Been thanked: 0 time

Re: Order of dataset in dataset concatenation

 

Re: Order of dataset in dataset concatenation

Postby Akatsukami » Tue Oct 08, 2013 11:44 pm

This was true in the past, but is no longer so. However, since many application outsourcers like to run OS/MFT on their 370/195s to save a rupee, we still disseminate this advice.
"You have sat too long for any good you have been doing lately ... Depart, I say; and let us have done with you. In the name of God, go!" -- what I say to a junior programmer at least once a day
User avatar
Akatsukami
Global moderator
 
Posts: 1053
Joined: Sat Oct 16, 2010 2:31 am
Location: Bloomington, IL
Has thanked: 6 times
Been thanked: 51 times

Re: Order of dataset in dataset concatenation

Postby nikesh_rai » Tue Oct 08, 2013 11:58 pm

So, is there any advantage of keeping larger block size at first. because, what we know about block size is that it makes I/O operation faster, but it will be applicable as per the block size of each dataset. It is not like, once system will identify the largest block size and will process all the datasets with that block size only.

Please correct me if I am wrong.
Thanks
Nikesh Rai
nikesh_rai
 
Posts: 192
Joined: Tue Oct 18, 2011 1:27 am
Has thanked: 17 times
Been thanked: 0 time

Re: Order of dataset in dataset concatenation

Postby Akatsukami » Wed Oct 09, 2013 12:08 am

So far as I know, there is no advantage, although someone like Dr. Sorichetti or Mr. Myers, whose knowledge of the internals of the operating system is far in advance of mine, would be a better guide in this.
"You have sat too long for any good you have been doing lately ... Depart, I say; and let us have done with you. In the name of God, go!" -- what I say to a junior programmer at least once a day
User avatar
Akatsukami
Global moderator
 
Posts: 1053
Joined: Sat Oct 16, 2010 2:31 am
Location: Bloomington, IL
Has thanked: 6 times
Been thanked: 51 times

Re: Order of dataset in dataset concatenation

Postby enrico-sorichetti » Wed Oct 09, 2013 12:19 am

IIRC, once upon a time the first dataset characteristics where used to build all the control blocks needed for the I/O

I do not remember when it was made available the possibility to specify a BLKSIZE on the first DD
in order to build the control blocks chain for the largest BLKSIZE

and provide for arbitrary concatenations .

PS.
when in doubt I always used to add a DCB=(BLKSIZE=32760) to the first DD of the concatenation of LRECL=80 datasets
cheers
enrico
When I tell somebody to RTFM or STFW I usually have the page open in another tab/window of my browser,
so that I am sure that the information requested can be reached with a very small effort
enrico-sorichetti
Global moderator
 
Posts: 2644
Joined: Fri Apr 18, 2008 11:25 pm
Has thanked: 0 time
Been thanked: 130 times

Re: Order of dataset in dataset concatenation

Postby dick scherrer » Wed Oct 09, 2013 3:11 am

Hello,

I do not remember when it was made available the possibility to specify a BLKSIZE on the first DD
in order to build the control blocks chain for the largest BLKSIZE
I also do not remember the date, but it was more than 30 years ago.
Hope this helps,
d.sch.
User avatar
dick scherrer
Global moderator
 
Posts: 6304
Joined: Sat Jun 09, 2007 8:58 am
Has thanked: 3 times
Been thanked: 91 times

Re: Order of dataset in dataset concatenation

Postby BillyBoyo » Wed Oct 09, 2013 3:58 am

It won't affect the performance, the physical block on the physical media for any given dataset is the largest block that can be read for that dataset. no matter what override is specified on the DD. The largest blocksize had to be first, simply so that there was enough space allocated to read a block in to. No longer the case.

These users thanked the author BillyBoyo for the post:
nikesh_rai (Wed Oct 09, 2013 10:39 am)
BillyBoyo
Global moderator
 
Posts: 3804
Joined: Tue Jan 25, 2011 12:02 am
Has thanked: 22 times
Been thanked: 264 times

Re: Order of dataset in dataset concatenation

Postby steve-myers » Wed Oct 09, 2013 7:55 am

nikesh_rai conveniently forgot to clearly state if this is for PDS concatenation or sequential data set concatenation.

The largest BLKSIZE first rule was mainly for PDS concatenation. Some years ago (but less than the 30 years ago someone mentioned) IBM changed PDS concatenation so it would automatically use the largest BLKSIZE in the concatenation.

These users thanked the author steve-myers for the post:
nikesh_rai (Wed Oct 09, 2013 10:43 am)
steve-myers
Global moderator
 
Posts: 1886
Joined: Thu Jun 03, 2010 6:21 pm
Has thanked: 4 times
Been thanked: 197 times

Re: Order of dataset in dataset concatenation

Postby nikesh_rai » Wed Oct 09, 2013 10:38 am

Thanks to all of you for clarification.. :)

nikesh_rai conveniently forgot to clearly state if this is for PDS concatenation or sequential data set concatenation.


I was looking for sequential dataset..
Thanks
Nikesh Rai
nikesh_rai
 
Posts: 192
Joined: Tue Oct 18, 2011 1:27 am
Has thanked: 17 times
Been thanked: 0 time


Return to JCL

 


  • Related topics
    Replies
    Views
    Last post