-----Original Message-----
From: IBM Mainframe Discussion List [mailto:[email protected]] On
Behalf Of Ted MacNEIL
Sent: Wednesday, February 18, 2009 10:15 PM
To: [email protected]
Subject: Re: EXECIO
Okay!
I surrender!
It wasn't there, at the time.
We blew the files off the map!
Sorry, but it happened!
<SNIP>
Mark's post got me thinking. So I did a quick search and found this:
Perhaps II00587 (Last Changed ........ 89/09/28)
I wonder if it might partly describe the problem you have had?
I know for a fact that a certain ISV has caused problems with BLDL &
STOW. At the time I worked on ACS/WYLBUR, two of my people had worked in
Common O/C/E L2 and informed me of a few issues here. There are other
APARs dealing with the associated problems, but I thought you might want
to read this from all the way back in the '80s (out of the afore
mentioned APAR II00587):
PROBLEM SUMMARY:
A) THE TTR POINTER, THE DS1LSTAR FIELD, IS MAINTAINED IN
THE FORMAT1 DSCB. ITS FUNCTION IS TO POINT TO THE LAST USED
BLOCK AND THE LAST USED TRACK. THIS FIELD IS CRUCIAL TO
POSITIONING THE NEXT MEMBER WRITTEN TO A PDS.
B) THE PDF EDITOR USES THE FOLLOWING SEQUENCE TO AVOID
DATA INTEGRITY EXPOSURES WHEN UPDATING A PDS MEMBER:
1) OPEN FOR READ
2) READ MEMBER INTO STORAGE
3) CLOSE DATA SET
AND AT SAVE TIME:
4) ENQUEUE RESERVE ON THE DATA SET
5) OPEN FOR WRITE
6) WRITE
7) STOW
8) CLOSE
9) RELEASE
THIS IS ALL DONE USING EXISTING IBM DATA MANAGEMENT SERVICES
AND LEAVES NO POSSIBILITY FOR INVALIDATION OF THE DS1LSTAR
FIELD ON AN UNMODIFIED IBM SYSTEM. AT THE SAME TIME, IT
ALLOWS MULTIPLE USERS TO EDIT DIFFERENT MEMBERS OF THE SAME
PARTITIONED DATA SET.
C) THE FIRST ACCESS OF EACH DAY CAUSES THE FORMAT1 DSCB
TO BE READ, UPDATED WITH THE CURRENT DATE, AND REWRITTEN.
IF THIS TAKES PLACE WHILE THE DATA SET IS OPEN FOR OUTPUT
OR UPDATE, THE DS1LSTAR COULD BE INVALIDATED. THIS UNIQUE
PROBLEM, COMMONLY KNOWN AS 'THE MIDNIGHT PROBLEM', WAS
DOCUMENTED BY O/C/EOV APAR OZ44857 (CLOSED 'PRS'). THIS
APAR HAS BEEN PURGED FROM RETAIN AND IS NO LONGER VISIBLE.
SEE NEW APAR OY07766.
D) SOME NON-IBM DISK MANAGEMENT PACKAGES HAVE THE OPTION
OF FORCING A REWRITE OF THE FORMAT1 DSCB AT EVERY OPEN.
THIS CAN RESULT IN AN INVALID POINTER IN THE DS1LSTAR FIELD
AND A DAMAGED DIRECTORY. USERS RUNNING IN THIS MODE ARE
RISKING A DUPLICATE TTR EVERY TIME A MEMBER IS SAVED BY
PDF.
Regards,
Steve Thompson
-- Opinions expressed by poster may not reflect those of poster's
employer. --
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