Although Ken's point about the dangers of UNDEDLOK is well taken, the
potential damage is no worse, it would seem, than HALTing the system while
database accessors are deadlocked.  At least with UNDEDLOK you get to choose
which process dies, which may serve to mitigate the damage.  Still, it is
dangerous, and anytime you encounter a deadlock, you should take steps to
prevent its recurrence, rather than depending on UNDEDLOK.

Ken, I tried unsuccessfully to find the new version of UNDEDLOK on the ITRC.
A search on "UNDEDLOK" yielded nothing but some old documents.  Can you give
some more information about its location?

-----Original Message-----
From: Sletten Kenneth W KPWA [mailto:[log in to unmask]]
Sent: Monday, June 25, 2001 5:30 PM
To: [log in to unmask]
Subject: New version of UNDEDLOK for TurboIMAGE now available from HP.


FYI all who think they might ever want to run UNDEDLOK:

The version of UNDEDLOK.PRVXL.TELESUP shipped with MPE
6.5 PP2 is not compatible with the latest version of TurboIMAGE on
6.5.  The "as shipped" version of UNDEDLOK on 6.5 PP2 is
A.65.00;  that vers is good ONLY through TurboIMAGE vers C.07.xx.

I haven't had to try and use UNDEDLOK in a long time, but for those
who think they might want to:  Be advised that UNDEDLOK version
A.65.01 is now available from the ITRC;  this version is compatible
with TurboIMAGE version C.07.xx on MPE 5.5 and 6.0;  and with
TurboIMAGE versions C.07.xx through C.09.xx on MPE 6.5  (we are
running TurboIMAGE C.09.02).

WARNING       WARNING        WARNING       WARNING

UNDEDLOK can and will indeed "unwind" TurboIMAGE locks in at
least some cases, *** BUT ***:  Be advised and cautioned that
UNDEDLOK knows NOTHING AT ALL about the logical structure
of the TurboIMAGE transactions in your applications.  UNDEDLOK
will happily try and remove whatever lock you tell it to;  without the
*slightest* concern for what that might do to the logical integrity of
complex transactions.....:  i.e.:   If you ever contemplate using
UNDEDLOK on a production database, you better know what the
ramifications are for the program that is "hung"....

Note that I used UNDEDLOK to unwind a "simple" deadlock on our
production database 2-3 years ago, and all was well afterwards.
So at least in some cases it can allow you to avoid a reboot....

Ken Sletten
SIGImage/SQL Chair

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