How can I force an entity type to process one at a time (single threaded) when we have multiple process engines defined?

Document ID : KB000054609
Last Modified Date : 14/02/2018
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Running multiple sub-tasks, and need to single thread an entity type - IMS PSBs and ACBs which require running a program to update these dynamically. Doing two PSB's at the same time caused two sub tasks to hang in a deadly embrace over the ACB data sets. Cancelling the sub tasks did not help, and we had to restart Alchemist.

Is there an alternative to running the PSB's in separate requests?


Try using the ENQUEUE keyword on the PCL DD statement for the TFILE data set that needs to be single-threaded.

ENQUEUE parameter:

  • Identifies qnames to associate with the data set allocated.

  • When PCL allocates the data set, PCL generates exclusive ENQUEUES with the qnames and an rname of the 44-character data-set name.

  • You can have up to eight qnames in one ENQUEUE parm.

  • Qname can be up to 8 bytes/characters in length.

  • You can use any name that you want, such as "IMSPSBS". (See below for specific use of qnames SYSIEWLP and SPFDSN)

You do not need to (and should not) use the ENQUEUE parameter under these circumstances:

  1. The linkage editor automatically provides this protection by enqueuing the SYSLMOD library with qname SYSIEWLP.

  2. The Alchemist utility ZCBTCOPY also provides automatic protection.

When other programs create target files, use the PCL ENQUEUE parameter to serialize access to the library, for example,


NOTE: Always use the ENQUEUE name SPFDSN for source and DBRM libraries, and the ENQUEUE name SYSIEWLP for load libraries.

DD Statement Syntax:

    //{ddname DD JCL-subparameters}, 
    // {FORMAT=({[STD]|[XNUM]|[NONUM]|[COBOL]|[DATA]}, 
    // {[NOSUB]|[SUB]|[DEFERSUB]})}, 
    // [ENQUEUE=(qname1[,qname2]...)] 


    //              ...,ENQUEUE= IMSPSBS