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Ramkumarinfo · Beginner Joined: 06 Jun 2007 Posts: 5 Topics: 3

Hi,

I am new to the mainframe environment. As I was reading
the batch programs I noticed that before explicitly commiting data to db2 tables,
All the datasets are closed and re-opended after the commit.
Can anybody explain why the datasets need to be closed before an
explicit commit in batch programs?

Thanks and Regards,
Ram

dbzTHEdinosauer · Posted: Thu Jun 07, 2007 4:34 am Post subject:

Ramkumarinfo,

Back in the days the stability of operating systems required (not required, if you did not want to spend all night trying to restart!) this behaviour.

reason: Dataset reading/writing is mostly done in the buffer, only when the buffers are full is data written to DASD. Earlier releases of operating systems software could not guarantee a flush of the buffers to DASD after an ABEND in the run-unit. Thus, restart was a pain, because the DB2 and the qsam/vsam did not match (something had been left in the buffer).

I personnally do not close/reopen with a commit, mainly because the sites that I work at have up-to-date/state-of-the-art operating systems and such silliness as losing stuff in the buffer does not happen.

but, if that is the shop standard, I would follow it!
_________________
Dick Brenholtz
American living in Varel, Germany

Ramkumarinfo · Beginner Joined: 06 Jun 2007 Posts: 5 Topics: 3

Thanks for your reply,

I am not able to understand still one thing with these code.
They close even the datasets that are opened for read only before
an explicit commit and re-open after the commit is succesfull.
Why they do this? Is it just blindly doing things uniformly or they
have resons for?

Thanks and Regards,
Ram

dbzTHEdinosauer · Posted: Thu Jun 07, 2007 6:26 am Post subject:

I always have a checkpoint/restart row in some table. Contained in the row was data indicating how many reads had been accomplished, was used to reposition the read dataset during restart.

your run-unit must have some repositioning logic after the close/open which probably is also used during restart. Saves having two types of open logic. the read counter is either zero (begining of new job) or a number indicating restart/reopen after commit.

kolusu · Posted: Thu Jun 07, 2007 6:56 am Post subject: