Warm Restart

A warm restart brings CICS back up after a normal, controlled shutdown. CICS restores the state it saved at shutdown, so users and applications find things mostly as they left them.

What a warm restart restores

• At normal shutdown CICS writes a warm keypoint and updates the global catalog with the state of the region.
• A warm restart restores terminal definitions, intrapartition transient data queues, auxiliary temporary storage queues and program status.
• It also restores file open/closed status and other resource states, so applications resume quickly.
• In-flight tasks are NOT restored - only tasks that had already finished. Users must sign on and start new transactions.

When to use a warm restart

• Use it after any planned shutdown: system maintenance, applying PTFs, changing resource definitions or an IPL of the LPAR.
• It is faster than a cold start because definitions and queue contents do not have to be rebuilt.
• Never use warm restart after a crash or cancel - there is no valid keypoint, and you need emergency restart instead.

Requesting a warm restart

• Pass START=WARM to DFHSIP in the startup JCL:-
  //CICSSTEP EXEC PGM=DFHSIP,
  // PARM='SI,START=WARM,APPLID=CICSPROD'
• In practice most shops use START=AUTO, which selects WARM automatically when the previous shutdown was normal.
• After the restart, verify with CEMT INQUIRE that key files, programs and transactions are in the expected state.