Internal trace table

The CICS® internal trace table is held in storage in the CICS region. It is allocated at an early stage during CICS initialization, and it exists for the whole of the CICS run.

CICS obtains MVS™ 64-bit (above-the-bar) storage (outside the CICS DSAs) for the internal trace table.

You use the TRTABSZ system initialization parameter to specify the size of the internal trace table at CICS startup. Its minimum size is 16 KB, and its maximum size is 1 GB. The default size is 12288 KB (12 MB).

Every CICS region always has an internal trace table. Even if internal tracing has not been started for the CICS region, the internal trace table is used as a buffer for the other trace destinations. Trace entries are built there and copied to the auxiliary trace data sets or to GTF trace if those destinations are started.

In addition, exception trace entries are always written to the internal trace table, even if no trace destinations are currently started. Other trace destinations that are currently started get the exception trace entry as well, but the entry always goes to the internal trace table even if you have turned tracing off completely. This function provides first failure data capture.

The internal trace table wraps when it is full. When the end of the table is reached, the next trace entry to be directed to the internal trace table goes to the start, and overlays the trace entry that was formerly there. You can increase or decrease the size of the internal trace table while CICS is running, but if you do so you lose all of the trace data that was present in the table at the time of the change.

For a transaction dump, CICS copies the current internal trace table to produce the transaction dump trace table. You use the TRTRANSZ system initialization parameter to specify the size of the transaction dump trace table, which is created in MVS storage in 64-bit (above-the-bar) storage.

The internal trace table is most useful for background tracing or when you do not need to capture an extensive set of trace entries. If you need to trace CICS system activity over a long period, or if you need many trace entries over a short period, one of the other trace destinations is likely to be more appropriate.