Gary_Cherlet

XTIOT

Discussion created by Gary_Cherlet on Jul 18, 2012
Latest reply on Jul 19, 2012 by Gary_Cherlet
Yesterday I started up my R18 IDMS system on an LPAR with z/OS 1.13 . Our current z/OS level is 1.11 . It looks like our Sys Progs have decided to go straight for the unlucky number without dithering around with 1.12.

It seems to work just fine, but it has presented me with a bit of information which I am not sure what to do with.

From z/OS 1.12 onwards there is a new SYS1.PARMLIB parameter called NON_VSAM_XTIOT. It defaults to NO.

When my system starts up I get a message telling me that this parameter is set to NO. Which I know already.

[font=Courier New]12.13.12 JOB09339 IEF403I TIDMS14D - STARTED - TIME=12.13.12
12.13.12 JOB09339 +IDMS DC016109 XTIOT disabled for dynamic allocation[font]

Obviously I am very grateful for this snippet of information. There is even an explanation..

[font=Courier New] D MESS DC016109
MESSAGE ID DC016109

LINE 1
SEVERITY 0
DESTINATION LOG
O.S. DEST CODE 0
O.S. ROUTE CODE 0
MESSAGE TEXT XTIOT disabled for dynamic allocation

DEFINITION DC016109 XTIOT disabled for dynamic allocation
The use of XTIOT for dynamic allocation of CA IDMS
database files for Central Version processing is
controlled by the setting of NON_VSAM_XTIOT statement
in the DEVSUPxx member of SYS1.PARMLIB. In z/OS 1.12,
a setting of NON_VSAM_XTIOT=NO (the default) will
disable the use of XTIOT for dynamic allocation and
normal TIOT will be used for dynamic allocation.
COMMENTS Module(s) = RHDCOMVS[font]


Which is great. What I can't find out is whether I should set it to YES or NO. The IBM documentation says:

In z/OS V1R12, BSAM, BPAM, QSAM and OCE are enhanced to support the existing XTIOT (extended task input/output table), UCB nocapture, and DSAB-above-the-line options of dynamic allocation. Previously, VSAM and EXCP were the only access methods to support these dynamic allocation options. In
V1R12 the EXCP support is enhanced and BSAM, BPAM and QSAM support is provided. This new support applies to dynamic allocation of DASD, tape, and dummy data sets, and cases where PATH= is coded. EXCP support including the EXCPVR and XDAP macros is also affected. These enhancements provide virtual storage constraint relief especially in the areas of DASD and tape support, and enable you to have more than about 3200 dynamically-allocated data sets.


So I assumed that IDMS was not using it at z/OS 1.11 because I believe that IDMS probably uses a bit of BSAM and QSAM and not just EXCP mode. However a source at CA says that it does use XTIOT from R15 onwards. They further suggest I should set it to YES unless I prefer to set it to NO.

I don't really know what is best for me to do in this circumstance. I have adopted the plan of assigning Heads to YES and Tails to NO and begun an experiment of statistical analysis involving a coin. This seems to be working.

Has anybody got a better vision of what I am meant to do with this parameter?

Chris Trayler

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