A batch job that used to be fast is now slow

Separate waiting from working

First establish whether the job is using CPU or waiting. In SDSF DA, a job with high elapsed time and low CPU is blocked; a job with high CPU is genuinely doing more work.

If it is waiting

• A DB2 lock — check for -911 or -913 in the log, or ask a DBA to look at lock waits.
• A dataset enqueue — another job holds it exclusively.
• Tape mounts or an outstanding console reply.
• Contention with other work that has been rescheduled into the same window.

If it is working harder

• Data volume grew. Check the input record counts against previous runs.
• A DB2 access path changed after a rebind or new statistics — compare EXPLAIN output.
• A VSAM file needs reorganising; check LISTCAT for CI and CA splits.
• An index was dropped or is no longer being used.
• A change went in that added processing per record.