Interpreting VTAM statistics

The "peak RPLs posted" includes only the receive-any RPLs defined by the RAPOOL system initialization parameter. In non-HPO systems, the value shown can be larger than the value specified for RAPOOL, because CICS® reissues each receive-any request as soon as the input message associated with the posted RPL has been disposed of. VTAM® may well cause this reissued receive-any RPL to be posted during the current dispatch of terminal control. While this does not necessarily indicate a performance problem, a number much higher than the number of receive-any requests specified via RAPOOL may indicate, for MVS™, that VTAM was required to queue incoming messages in subpool 229 when no receive-any was available to accept the input. You should limit this VTAM queueing activity by providing a sufficient number of receive-any requests to handle all but the input message rate peaks.

In addition to indicating whether the value for the RAPOOL system initialization parameter is large enough, you can also use the "maximum number of RPLs posted" statistic (A03RPLX) to determine other information. This depends upon whether your MVS system has HPO or not.

For HPO, RAPOOL(A,B) allows the user to tune the active count (B). The size of the pool (A) should be dependent on the speed at which they get processed. The active count (B) has to be able to satisfy VTAM at any given time, and is dependent on the inbound message rate for receive-any requests.

Here is an example to illustrate the differences for an HPO and a non-HPO system. Suppose two similar CICS executions use a RAPOOL value of 2 for both runs. The number of RPLs posted in the MVS/HPO run is 2, while the MVS/non-HPO run is 31. This difference is better understood when we look at the next item in the statistics.

This item is not printed if the maximum number of RPLs posted is zero. In our example, let us say that the MVS/HPO system reached the maximum 495 times. The non-HPO MVS system reached the maximum of 31 only once. You might deduce from this that the pool is probably too small (RAPOOL=2) for the HPO system and it needs to be increased. An appreciable increase in the RAPOOL value, from 2 to, say, 6 or more, should be tried. As you can see from the example given below, the RAPOOL value was increased to 8 and the maximum was reached only 16 times:

     MAXIMUM NUMBER OF RPLS POSTED         8
     NUMBER OF TIMES REACHED MAXIMUM      16

In a non-HPO system, these two statistics are less useful, except that, if the maximum number of RPLs posted is less than RAPOOL, RAPOOL can be reduced, thereby saving virtual storage.

VTAM SOS simply means that a CICS request for service from VTAM was rejected with a VTAM sense code indicating that VTAM was unable to acquire the storage required to service the request. VTAM does not give any further information to CICS, such as what storage it was unable to acquire.

This situation most commonly arises at network startup or shutdown when CICS is trying to schedule requests concurrently, to a larger number of terminals than during normal execution. If the count is not very high, it is probably not worth tracking down. In any case, CICS automatically retries the failing requests later on.

If your network is growing, however, you should monitor this statistic and, if the count is starting to increase, you should take action. Use D NET,BFRUSE to check if VTAM is short on storage in its own region and increase VTAM allocations accordingly if this is required.

The maximum value for this statistic is 99, at which time a message is sent to the console and the counter is reset to zero. However, VTAM controls its own buffers and gives you a facility to monitor buffer usage.

If you feel that D NET,BFRUSE is insufficient, you can activate SMS tracing in VTAM to sample buffer activity at regular intervals. If you have installed NetView®, you can also have dynamic displays of the data that is obtained with D NET, BFRUSE.

For more information, see the CICS statistics tables in topic VTAM statistics.

Related reference
Back to full list of statistics
Interpreting CICS statistics
Full listing and DFHSTUP reports for these statistics
VTAM statistics
DFH0STAT reports for these statistics
Autoinstall and VTAM Report
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