CICS TS Performance

In the process of debugging a problem for a customer I found that CICS TS was doing this ...

. VTAM RECEIVE ANY is issued for a length of 256 bytes

. At some point later the receive is completed and the RPL EXIT scheduled
. RPL EXIT executes issuing a VTAM CHECK Macro
. RPL EXIT processes the 1st 256 bytes of data
. RPL EXIT allocates a buffer for the remaining input bytes
. RPL EXIT issues a VTAM RECEIVE SPECific to read the remaining bytes.
. RPL EXIT completes

. VTAM has data available to complete RECEIVE Specific
. RPL EXIT is scheduled
. RPL EXIT executes issuing a VTAM CHECK macro
. RPL EXIT processed the remaining data and posts CICS
. RPL EXIT issues a RESETSR to change the CS/CA mode back to Continue Any
. RPL EXIT completes

Thinking that this process was messy and a lot of CPU overhead I discovered the RAPOOL and RAMAX SIT parameters. The RAPOOL parameter controls the number of RECEIVE ANY RPL CICS has available. The default is 50 and is fine for most systems. The RAMAX value is the size of the RECEIVE ANY buffer. The default is 256 and is terrible. Since these buffers are allocated out of 31-bit storage using a value of 8096 is much better. 8096 is a good value for a 3270 receive buffer. Virtually any 3270 input will fit into this buffer with a single RECEIVE request. And, after all 50 x 8K is only 400K of 31-bit buffer space.

After changing RAPOOL=50,RAMAX=8096 I looked into the performance again.

. VTAM RECEIVE ANY is issued for a length of 8096 bytes

. At some point later the receive is completed and the RPL EXIT scheduled
. RPL EXIT executes issuing a VTAM CHECK Macro
. RPL EXIT processes the all of the input data and posts CICS
. RPL EXIT completes

You can see the process is much shorter, fewer VTAM macros are used and several passes through the dispatcher and waits are eliminated. I would estimate a 60% reduction (or more) in CPU usage for this process too.

For those of you still running CICS/VSE 2.3 try RAPOOL=10,RAMAX=8096 and you will still see the improvement.

Enjoy.

Regards,
Jeff