We propose introducing configurable maximum thresholds and rollover policies for FDC file generation to protect host operating systems from disk-exhaustion outages.

Problem Statement:

While FDC files are essential diagnostic tools when IBM MQ encounters an unexpected error or exception, the current error-logging behavior poses an operational risk to underlying file systems.In a recent QA environment issue, an unhandled repeating exception caused an FDC file (e.g., AMQxxxx.FDC) to continuously append data until it exceeded 45 GB. This runaway logging consumed all available disk space, leading to server-wide file system saturation and impacting surrounding services and Queue Managers. Currently, while IBM MQ provides suppressions for certain repeated error logs, there is no hard upper limit or built-in log rotation mechanism for an individual FDC file when an uncontrolled loop occurs.

Proposed Solution / Enhancement Request
We propose introducing configurable maximum thresholds and rollover policies for FDC file generation to protect host operating systems from disk-exhaustion outages.

Maximum File Size Cap (MaxFDCFileSize):
Introduce an optional tuning parameter in qm.ini or mqs.ini allowing administrators to set a hard maximum size for any single .FDC file (e.g., default or cap at 100MB/500MB).

FDC File Rollover / Truncation (MaxFDCFiles):
Implement a rotation mechanism similar to standard log rotators:

When an FDC file reaches MaxFDCFileSize, freeze/close the file and append a counter (e.g., AMQxxxx.0.FDC, AMQxxxx.1.FDC), or truncate the least significant middle section while preserving the initial stack trace and final state.

Allow setting a maximum count of rolled-over FDC files per process or Queue Manager.

Alerting / Rate Limiting:
If an FDC file triggers a size cap or rollover event, emit a distinct system log message (e.g., to AMQERR01.LOG or syslog) warning that diagnostic output is being capped due to high frequency/volume.