ca.portal.admin

Re: [IDMSVENDOR-L] now to prevent space management page deadlocks?=

Discussion created by ca.portal.admin on Jul 13, 2010
??

when i dirst posted - i was not sure myself to which you were referring

now I can say the former two data pages locked by space management




and Kay hit it right on the head - this was a ""let's add 60000 record
occurances to an area that was build to hold (and has held) 10000
occurrances - AND LETS NOT TELL THE DBAs"" ....

my first question (that I can repeat here) was: how often does the purge
run - to which the answer was (of course) what is this purge thing of
which you speak?

at first i extended to double the size - but of course no one could tell
me how may ROs would be added - so the fist extend failed - i never got an
answer - so i extended it to hold 100000

i wanted to wait for the shake-out of this before i did an UL/RL (though
many times we are never given an outage to do an UL/RL)


Chris Hoelscher
IDMS/DB2 System & Database Architect
Humana Inc
502-476-2538
choelscher@humana.com

you only need to test the programs that you want to work correctly






From:
donjcasey@COMCAST.NET
To:
IDMSVENDOR-L@LISTSERV.IUASSN.COM
Date:
07/12/2010 11:30 AM
Subject:
Re: [IDMSVENDOR-L] now to prevent space management page deadlocks???
Sent by:
IDMS 3rd-party providers forum <IDMSVENDOR-L@LISTSERV.IUASSN.COM>



I'm probably not fully awake yet.

By 'SMP deadlock' do you mean a 'space on this here page' deadlock (line
index 255) or a lock on the SMP page itself?

If the latter, I don't recall any locking taking place on the SMP pages.

If the former, then if two run units are attempting to modify space on the
same page, and have some other resource conflict, then yes, you can get
deadlocks. IDMS locks this artificial line index (highest possible, based
on radix if I remember correctly) in order to ensure a rollback can take
place (can't give up space deleted for a new record until IDMS is sure
that space is going to stick around).

As to what things make this more common; I need more coffee.

Don Casey
Principal Consultant
Run Right, LLC

----- Original Message -----
From: Chris Hoelscher <choelscher@HUMANA.COM>
To: IDMS-L@LISTSERV.IUASSN.COM
Sent: Mon, 12 Jul 2010 14:19:37 -0000 (UTC)
Subject: now to prevent space management page deadlocks???

i think we all know the bad programming code that can lead to db-key
deadlocks - but are SMP deadlocks just a matter of coincidence?
can they just occur because of where record occurrence STORES or DELETES
(or MODIFYs) are intended to take place?


thanks,
Chris Hoelscher
IDMS/DB2 System & Database Architect
Humana Inc
502-476-2538
choelscher@humana.com

you only need to test the programs that you want to work correctly




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Re: [IDMSVENDOR-L] now to prevent space management page deadlocks???
"You know - this sounds to me like one of those CAS areas that the records are stored DIR(ect) - doesn't matter how many records for an area sized for how many records. The problem is that with a DBKEY of -1 (recommended for Logging, Audit, etc type of areas) the system looks through the SMP pages to find the first page with free space - it then adds the record into that page.

All the previous pages being > 80% full the last SMP needs to be updated, plus the page that the record is being added into has a page level lock (because Sr1 is updated due to space available change - this happens too if variable record length record changes length on MODify) - so there's at least a couple of page level locks.

This may or may not be your scenario - but it is common in CAS and many non-CAS applications were built with this concept so as to get a ""time sequence"" or ""flat file"" out of IDMS-DB. There are other solutions - but it is good to be aware of the problems associated with the DIR storage mode and DBKEY of -1 approach !

HTH - cheers - Gary

Gary Cherlet
Justice Technology Services
Department of Justice, SA Government

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