PXX Master List Dump: Multi-User Facility (MUF) Availability and Performance Impact (Datacom)

Products

• Datacom

Issue/Introduction

Multi-User Facility (MUF) diagnostic operations, specifically PXX master list dumps, are often analyzed for their impact on system responsiveness. This article clarifies MUF behavior during dump generation and provides methods to mitigate performance issues.

Symptoms

Events observed coinciding with PXX dump activity include:

• CICS tasks waiting on ECBLIST.
• "Max Task" events.
• Observed system performance degradation or apparent freezes.
• PXX START/END messages in MUF joblog for various return codes, e.g.  09(015), 16(012), or 24(013).

Environment

• Datacom 15.1
• z/OS

Cause

When the SYSOUT MUF startup parameter is specified, the PXX master list dump is written to a dynamically allocated JES spool dataset (SYSOUT). If the SYSOUT parameter is not specified, the master list dumps are written to the PXX dataset. While the MUF does not freeze, system performance can be impacted by the high volume of output written to the SYSOUT or PXX dataset.

Resolution

The PXX master list dump process does not pause, freeze, or place the MUF into a wait state. MUF remains available for task processing during this operation.

Follow these steps to understand and manage PXX dump behavior:

1. Verify PXX dumps are written to SYSOUT: Confirm that the MUF startup option SYSOUT is specified so PXX master list dumps are written to SYSOUT.
2. Evaluate Resource Usage: Determine if system performance is being impacted by the volume of data written to the SYSOUT rather than an internal MUF hang.
3. Suppress Unnecessary PXX Dumps: If frequent dumps cause excessive SYSOUT output, use the RCERROR startup option to suppress specific return codes from generating a dump:
• RCERROR NO,NO,09015
• RCERROR NO,NO,16012
• RCERROR NO,NO,24013

 

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