z/OS Diagnostic Data Collection and Analysis

22.21. Writing trace data to in-storage buffers

System trace records are stored in the trace buffer of each process when the TraceFlagBuffer is switched on. The trace buffer is a ring; trace records are written sequentially into the buffer, and when the end of the buffer is reached, storage continues at the beginning of the buffer, overwriting older records. The size of the ring buffer is determined by the value of the TraceMaxSizeBuffer attribute. The default value is 131,072 bytes. The attribute can be set to any positive integer, but changes do not affect processes already running.

The ring buffer is the default destination for system trace records. Storing trace records in the ring buffer puts the least load on the process being traced, ...