DB2/OS390 wait reasons 
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 DB2/OS390 wait reasons
In examining class 3 wait times for some tasks running in DB2/OS390 V6.1 I
am finding that a majority of the time is being spent in class 3 wait, under
the heading "delete/define/extend".

What types of things could we look at to reduce this time?  It is as much as
80-90% of the total class 3 time, and class 3 is > 90% of class 1 time.
Syslgrng and open/close times are small.  Could this be related to HSM
times, and if so, how would I determine this with certainty??

thanks

Kenneth Lahn



Fri, 22 Aug 2003 21:13:26 GMT
 DB2/OS390 wait reasons

Is the time TCB/SRB mostly in or out of DB2?

Just by seeing delete/define/extend, i guess it has to do with underlying db2 or
app VSAM datasets.
Primary allocation may not be large enough or ext space may be difficult to find
(big?). (?)

Do you know if the tasks are cics/ims related, do you run?  There maybe
overestimated values in this case.
(you may even get things such as total class 3 suspensions time greater than
class 2 elapsed time)
Parallel Sysplex and CP : CPU and suspension times may also be higher than in
reality.
(parallel processing)

Verify that you are not in presence of overestimated values. (somewhere in the
doc.)

The time difference between the classes can indicate if the time is spent in or
out of db2. (check the doc)

HSM ?  I don't even remember if this is the OMVS fs.
Even for overestimated values, it looks high to me.
I can't help much because of my limited knowledge of the PM.

Quote:

> In examining class 3 wait times for some tasks running in DB2/OS390 V6.1 I
> am finding that a majority of the time is being spent in class 3 wait, under
> the heading "delete/define/extend".

> What types of things could we look at to reduce this time?  It is as much as
> 80-90% of the total class 3 time, and class 3 is > 90% of class 1 time.
> Syslgrng and open/close times are small.  Could this be related to HSM
> times, and if so, how would I determine this with certainty??

> thanks

> Kenneth Lahn



Sat, 23 Aug 2003 18:33:55 GMT
 DB2/OS390 wait reasons

I digged a bit and i think the hsm you are talking about is DFSMShsm.
It is responsible for the Migrate, Hmigrate and the Hrecall.

There may be something wrong in the SMS definitions.
(or they are ok but the dataset/file is  being migrated because of its size, ... ?)

Stuff may be migrated too early from disk to tape.  The following may happen:
You create a file.
The file gets immediatly migrated to another pool. (cartridge, tape, other disks,
... ?)
Then, you need your file again.
The file has to be re-migrated on disk.
...

You (the job) may be waiting for the restore of the file (auto HRECALL).

That's one possibility.
If you can get SMS trace records or logs, it may help you see if it is that.

PM



Tue, 26 Aug 2003 16:15:32 GMT
 
 [ 3 post ] 

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