You can view enqueue locks from SDSF ENQ. If you see contention through SDSF ENQC, it can mean that messages are arriving faster than the writer task can write them to disk and clear the buffers. The default TRACING BUFFERS=100 setting is typically adequate, but on a heavily loaded system you could expand it to TRACING BUFFERS=500.

If messages are written to stdout, an enqueue lock is taken on the JES spool data set name immediately prior to the printf() statement. The lock is immediately released afterwards. This type of enqueue lock is designed to prevent z/OS abend S02A.

If legacy logging is in use so that messages are written to the DD DTLLOG that points to a JES print file, an enqueue lock is taken on the JES spool data set name immediately prior to writing to the file and released immediately afterwards.

When the process starts, the minor names of JES data sets used in enqueues are logged in message PWX-14540.