Datacom CDC DB03135W CDCU or CDCL BEHIND messages

Products

Datacom Datacom/DB Datacom/AD

Issue/Introduction

Using the Datacom CDC feature and getting excessive DB03135W messages:

DB03135W CDCM WARNING CDCU BEHIND

DB03135W CDCM WARNING CDCL BEHIND

Environment

z/OS

Cause

This warning is controlled by the CDCM_WARN startup option, which specifies the number of seconds behind the LXX that the CDCL or CDCU program can slip before a warning is issued.

CDCL task: Measured from the last log record it saw compared to the current last log record on DASD.
CDCU task: Measured from the oldest TSN record in the CDC database to the current last log record on DASD.
Polling frequency: Controlled by the CDCM_POLL option.

Resolution

When receiving persistent DB03135W messages, use the following steps to determine if the condition is expected workload lag or a potential task blockage:

Issue the STATUS_CDC Console Command:

Run STATUS_CDC to see the current state of CDCL and CDCU tasks.
Observe the "LAST CDC" vs. "LAST LXX" timestamps.
Check the "STATUS" column. A status of WAIT CDCL POLL or WAIT CDCU may indicate the task is waiting for work or potentially stuck.

Analyze MUF Logs for External Blockages:

Search MUF logs for errors occurring concurrently with the lag.
Look for DB01709I (Dynamic Extend) messages. If the CDC database is reaching the z/OS maximum number of extents (16), it may cause I/O delays or failures that freeze the CDC process.
Check for DB03163I messages. A high "WRAP" count in this message indicates the startup option CDC buffer may be too small.
Check for DB00321I LOG LXX WRAP messages. This indicates the LXX should be much larger to prevent a 'GAP' with CDC that will require manual intervention and substantial complexity to remove.

If STATUS_CDC confirms that the tasks are not making progress, or if logs show resource constraints:

Priority Check: Ensure the CDCU job is running with sufficient WLM priority. If it cannot keep up with the volume of work, it may require higher importance.
Dataset Capacity: If the CDCU is running as fast as possible but cannot keep current, the CDC base needs to be large enough to ensure it does not fill while waiting on the CDCU task.
Buffer Tuning: If DB03163I shows high WRAP values, consider increasing the CDC startup option buffer size (up to 16M).
LXX Size: If DB00321I WRAP messages are present, increase the size of the LXX.
Transient vs. Permanent: If the task is running but falling behind due to heavy transaction volume, this is expected behavior. If the task shows no movement in timestamps (e.g., stuck for hours), restart the CDCL/CDCU task to verify if it resumes processing.

Additional Information

For more information about Change Data Capture (CDC), please see the documentation topic Change Data Capture.

Also see Knowledge Base article 136601 Change Data Capture (CDC) Processing Overview