CICS Restart

A CICS restart is how a CICS region is started. The START system initialization option decides whether CICS begins completely fresh or picks up state left by the previous run.

Why the restart type matters

• After a planned shutdown you usually want a warm restart so terminals, queues and program status are restored.
• After a crash you need an emergency restart so in-flight work is backed out and data stays consistent.
• Choosing the wrong type can lose work or, worse, restart with inconsistent data - so operators must know what the previous shutdown looked like.
• The restart type is requested with the START option on the DFHSIP PARM, for example PARM='SI,START=WARM,...'.

The CICS restart types

• COLD - starts completely fresh; nothing from the previous run is restored. Used for a clean test region or after catalog damage.
• WARM - used after a normal shutdown; restores state saved in the warm keypoint and the global catalog.
• EMERGENCY - used after an abnormal end; recovers in-flight units of work from the system log.
• INITIAL - like COLD, but also formats (initializes) the CICS catalogs; used when the catalogs are new or damaged.
• AUTO - lets CICS decide: WARM if the previous shutdown was normal, EMERGENCY if it was abnormal. This is the usual production choice.

Starting CICS with a restart option

• The START value is passed to the DFHSIP program in the region startup JCL:-
  //CICSSTUP JOB (ACCT),'CICS START',CLASS=A,MSGCLASS=X
  //CICSSTEP EXEC PGM=DFHSIP,
  // PARM='SI,START=AUTO,APPLID=CICSPROD'
  //STEPLIB DD DSN=CICSTS.SDFHLOAD,DISP=SHR
• START=AUTO is the safest production default because CICS picks WARM or EMERGENCY based on how the region ended.
• APPLID must be unique - two regions cannot run with the same APPLID at the same time.