Datacom CICS performance WAIT EXTERNAL

Products

• Datacom
• DATACOM - AD
• Datacom/AD
• Datacom/DB

Issue/Introduction

A  Datacom CICS transaction is having performance problems.
A CICS trace shows  lots of WAIT EXTERNAL commands coming from program DCCTRPR.
Is this a problem?
What can be done to improve Datacom CICS Services performance?

Environment

z/OS and z/VSE operating systems

Resolution

A WAIT EXTERNAL in CICS is normal for a Datacom CICS program.
It means the program has sent a request to the Datacom MUF and is waiting for a response.
 
There is a performance enhancement which replaces CICS WAIT EXTERNAL with MVS WAIT/POST API for programs running under OPEN TCBs, it was introduced in PTF RO92668 for  DBC 15.0. 

It is best to also apply the latest PTF which delivers performance enhancements and all their pre-reqs, RO97469 for DBC 15.1.

For best performance code DBCVTPR with the following options, then assemble and link DBCVTPR and recycle CICS : 

DBCVTPR SKPSYNC=YES,CICSTRA=NO,FLOWTRA=NO,INTLTRA=NO,OPENAPI=YES,PGMNAME=TASK 

The other thing to check is if the application is defined as Threadsafe, the CICS program definition should have option CONCURRENCY(THREADSAFE). 

For Ideal, it is Threadsafe only if using load modules. If using VLS object it cannot run Threadsafe. 
The only programs that need to be defined with CONCURRENCY(THREADSAFE) are the VPE modules that interface with CICS, the VPEHJEnn and VPEHJNnn programs. 

Additional Information

Datacom documentation section Specifying Generation Options (DBCVTPR)
Also see Article 19090 for more information on Threadsafe.