Log tail deletion
The log tail is the oldest end of the log and is deleted by the log manager at each activity keypoint.
At each activity keypoint, the CICS® recovery manager requests that the log
manager deletes the tail of the system log by establishing a point
on the system log before which all older data blocks can be deleted.
Thus, if the oldest live
unit of work is in data block x,
the CICS log manager requests
the system logger to delete all data blocks older than x (x-1 and
older).
Long-running units of work that regularly initiate writes to the system log can prevent CICS from deleting completed units of work stretching back over many activity keypoints. See Long-running transactions.