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performance improvement through LRECL
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Rahul_kumar
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PostPosted: Wed Apr 27, 2011 10:10 am    Post subject: performance improvement through LRECL
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Hi,

my job was taking a lot of time and perfomance improvement was required.I noticed that the o/p file being created through that job was having a RECFM =VB and LRECL was very high as compared to the actual length of records in that file.Therby,I reduced the LRECL and the perffomance was reduced significantly.I would like to know how through LRECL; the execution time reduced significantly.My O/P file contains millions of records.

Thanks in advance
Rahul
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Garry Carroll

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PostPosted: Wed Apr 27, 2011 11:24 am    Post subject:
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First reaction is that, by reducing the, the blocking factor increased - i.e each EXCP (execute channel program) returned more records than previously. Are you sure, though, that you won't have records larger than the LRECL you have now specified?

Garry.
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Rahul_kumar
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PostPosted: Wed Apr 27, 2011 11:36 am    Post subject:
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Hi Garry,

Thanks for the reply.

Yes,we are sure that the maximum record length(REVFM=VB) won't increase more than LRECL.
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enrico-sorichetti

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PostPosted: Wed Apr 27, 2011 11:55 am    Post subject: Reply to: performance improvement through LRECL
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utter nonsense! and wrong conlusion... or wrong premises
review Your understanding of VB...
the lrecl in the dscb has nothing to do with the number of records stored in a block
it simply tells how large i the buffer that contains the data record for move mode access!

the number of records stored in a block depends only on the real record length

<bdw><rdw>data<rdw>data<rdw>data<rdw>data<rdw>data

the disk occupancy of datasets with the same record length pattern is the same period and does not depend on the maximum record length, only on the blocksize
test it if You do not believe it

on the other side given the poor understanding of VB around here
most probably there is some confusion
quite too often the posters talk about VB and FB without understanding what is going on


what was the disk occupancy before and after ???
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Rahul_kumar
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PostPosted: Wed Apr 27, 2011 1:07 pm    Post subject:
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Hi enrico,
The cobol module splices 2 i/p files into a VB file.The data in the i/p files is same before and after the run.just we reduced the LRECL of the O/P VB file and the CPU execution time reduced drastically.
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dbzTHEdinosauer

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PostPosted: Wed Apr 27, 2011 1:19 pm    Post subject:
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let us try to determine the o/p file attributes:
  • What was the original LRECL, DCB BLOCKSIZE, COBOL Module Blocksice for the output file
  • what were these values after the performance change?
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enrico-sorichetti

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PostPosted: Wed Apr 27, 2011 1:19 pm    Post subject: Reply to: performance improvement through LRECL
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if You are happy I am happy ( or better I do not care )
still Your understanding of data management is just plain wrong
and the conclusions You are drawing are wrong
You did not show any technical evidence of the fact
recfm , blksize, lrecl , space used, record count of the before
the same of the after ...
I/O counts of the before and the after

agin... show scientific evidence with all the data necessary to investigate

I am not telling that the elapsed and cpu observations are wrong,
I am just telling that the changes cannot depend on just a different LRECL allocation specification!
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dbzTHEdinosauer

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PostPosted: Wed Apr 27, 2011 1:36 pm    Post subject:
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Rahul_kumar,
how about answering my question if you want any help.
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Bill Woodger

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PostPosted: Wed Apr 27, 2011 1:59 pm    Post subject:
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Rahul_kumar wrote:
The data in the i/p files is same before and after the run.


Quite a normal situation.



I'd guess if you ever answer Dick, you'd have RECORD CONTAINS 0 in your Cobol program, thereby taking the LRECL from the JCL.
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enrico-sorichetti

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PostPosted: Wed Apr 27, 2011 2:03 pm    Post subject: Reply to: performance improvement through LRECL
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the TS talks about the OP ( output file )
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enrico-sorichetti

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PostPosted: Wed Apr 27, 2011 2:23 pm    Post subject: Reply to: performance improvement through LRECL
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Quote:
The cobol module splices 2 i/p files into a VB file.The data in the i/p files is same before and after the run.just we reduced the LRECL of the O/P VB file and the CPU execution time reduced drastically.


You posted the same message already twice and it was deleted
instead of blabbering, reply with the info we asked You.

if You are not willing to reply to what we ask You stop bothering

You ask for help we spend time on Your issue,
so show respect and good manners by replying to our questions
do You understand icon_evil.gif

if You do not come up with the info requested the topic will be locked and after a while deleted !
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dbzTHEdinosauer

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PostPosted: Wed Apr 27, 2011 2:24 pm    Post subject:
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Rahul_kumar wrote:
The cobol module splices 2 i/p files into a VB file.The data in the i/p files is same before and after the run.just we reduced the LRECL of the O/P VB file and the CPU execution time reduced drastically.


repeating that useless comment is not helping, and three times is not a charm!

changing the lrecl of the output file could have had the following effects:
  • original lrecl=14,000 new lrecl = 6,000 - impact - instead of 1 record per block, potentially 4
  • originally your code could have produced a max length vb every for every write, and the new code for the reduced lrecl managed to write a valid length'd vb record
  • you changed the block size
  • you did something else that you are not telling us
we are not in the habit of substantiating unfounded comments
based on the observance of someone who can not read and respond to questions.
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enrico-sorichetti

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PostPosted: Wed Apr 27, 2011 2:27 pm    Post subject: Reply to: performance improvement through LRECL
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at this point we can only guess that the program is just wrongly writing all the times a record with the maximum record length allowable

Quote:
I am just telling that the changes cannot depend on just a different LRECL allocation specification!
given/assuming that the program is correctly coded icon_biggrin.gif
but since the program is certainly badly coded then it is reasonable to expect a result according to the observation

as usually I make the mistake of assuming that the TS has done the due diligence and coded properly icon_evil.gif

certainly the storage salesdroid will be quite happy with his overachievement icon_biggrin.gif
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Rahul_kumar
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PostPosted: Wed Apr 27, 2011 3:06 pm    Post subject:
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Hi all,
Apologies for the late reply.actually I was refreshing the page for the reply and the same msg was being posted again & again.

The original LRECL was around 32000 and I reduced it to around 1000 bytes.Also,the same length was specified in the cobol program under FD section thereby that was also changed.I did'nt change the blk size or any other DCB parameter.

Also,I had also made a in the program to calculate the record length of VB file for each record.Since,previously the record length was 32K thereby the module was counting backward from 32K but now that was changed to 1000 bytes.But,this change did'nt made much difference and only after changing the LRECL,the time was reduced.
I want to know how by only changing the LRECL the performance can reduce significantly.
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dbzTHEdinosauer

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PostPosted: Wed Apr 27, 2011 4:33 pm    Post subject:
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you changed the lrecl to a point where there were more records per block.
at 32000, you only get 1.
at 1000, you get 27.

so you have reduced your read requirement by a factor of 27.

it was not the reducing the lrecl that had an affect.
if was significantly reducing the number of blocks that was effective in reducing cpu.
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enrico-sorichetti

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PostPosted: Wed Apr 27, 2011 4:35 pm    Post subject: Reply to: performance improvement through LRECL
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Quote:
I want to know how by only changing the LRECL the performance can reduce significantly.


for what friendly reason You keep refusing to post what we asked You to ...

allocation info for the <poor performing> dataset
allocation info for the <good performing> dataset

the space the space the space for the umpteen time the space used

if You are not able to reply to simple questions it would be wise to meditate on a career switch

the reason for the odd behavior is that the program was and probably is still wrong

it was and still takes the LRECL from the allocation rather than calculating it for each record based on the data layout

POST WHAT WE ASKED YOU FOR NOT YOUR HORSE MANURE


and also it would be a good idea to look at a physical dump of the block
if the RDW are all the same the program is wrong!

edited to change the f word to a less disturbing one icon_cool.gif
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enrico-sorichetti

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PostPosted: Wed Apr 27, 2011 4:36 pm    Post subject: Reply to: performance improvement through LRECL
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36_2_18.gif
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Robert Sample

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PostPosted: Wed Apr 27, 2011 4:51 pm    Post subject:
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Quote:
,I reduced the LRECL and the perffomance was reduced significantly.
Uh, no it did not. Something changed and improved performance -- but merely changing the LRECL pretty much had no impact of the overall performance and job throughput. Since LRECL is a LOGICAL concept and not a PHYSICAL contruct, there is no way that merely changing the LRECL would impact performance. Changing LRECL and thereby affecting block size, for example, could have a performance impact -- but it's not the LRECL change, per se, that is making the difference but the block size change.
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gcicchet

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PostPosted: Wed Apr 27, 2011 4:56 pm    Post subject:
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Hi,

run this across both files and show the results

Code:
//STEP0100 EXEC PGM=ICETOOL                                 
//TOOLMSG  DD SYSOUT=*                                     
//DFSMSG   DD SYSOUT=*                                     
//IN       DD DSN=input-file,DISP=SHR                       
//RPT      DD SYSOUT=*                                     
//TOOLIN   DD *                                             
  STATS FROM(IN) ON(VLEN)                                   
  OCCUR FROM(IN) LIST(RPT) BLANK -                         
   HEADER('LENGTH') ON(VLEN) -                             
   HEADER('COUNT') ON(VALCNT)                               
/*                                                         


That is if you have DFSORT.

Gerry
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vasanthz

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PostPosted: Wed Apr 27, 2011 5:21 pm    Post subject:
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Im not the TS or nor do i know him anyway, but Enrico's choice of words is are offending..

I have seen people advice others about not using 'ur' 'u' 'thx' saying that this is a professional forum and not SMS service, but which category does this belong to?
Quote:

for what fucking reason You keep refusing to post what we asked You to ...

Quote:
POST WHAT WE ASKED YOU FOR NOT YOUR HORSE MANURE




icon_rolleyes.gif
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