Managing the Transmission Control Queue
IBM® Connect:Direct® stores submitted Processes in the Transmission Control Queue (TCQ). The TCQ controls Process execution. The IBM Connect:Direct for z/OS® User Guide contains information about how to submit Processes, how to control those Processes once they are in the TCQ, the logical queues that make up the TCQ, and the status values of Processes in the TCQ. The TCQ consists of two interdependent VSAM data sets:
- The Transmission Control Queue, or TCQ, is a Relative Record Dataset (RRDS) which contains an internal form of the Process language of each Process and status flags.
- The Transmission Control Index, or TCX, is an RRDS containing a single record. It contains bitmaps, that indicate the availability of TCQ space.
The default size of the TCQ, as determined by the sample installation JCL, is 1000 records, but it can be as large as 4016 records if the sample TCX is used. The size of a Process can range from 1 to 43 records, depending upon the how many steps it contains. The average Process size varies by installation. If the average Process size is 5 records, the sample TCQ can contain approximately 200 Processes.
In order to use a TCQ with a capacity that exceeds 4016 records, the TCX must be defined with a record size and control interval (CI) size larger than those specified by default in the installation JCL. The IBM Connect:Direct for z/OS Configuration Guide and Program Directory for IBM Connect:Direct for z/OS contain more information about planning your space requirements.
To hold the maximum size Process (1 MB), the CISIZE of the TCQ must be at least 24 KB bytes.