Warm start

A warm start is the most common way to reinitialize IMS, and is the recommended way of restarting after a controlled shutdown of IMS. You should attempt a warm start only if IMS terminated in an orderly manner. You can specify a warm start by using the /NRESTART command.

Before starting IMS and entering the restart command, you must determine whether IMS should:

• Reload MSDBs
• Format specific system data sets during restart
• Activate specific security functions during restart

The following situations require you to reallocate and reformat specific system data sets after a controlled IMS shutdown:

• When a message queue data set is full (indicated by messages DFS206, DFS207, or DFS208) and IMS was shut down by an internally-generated /CHECKPOINT DUMPQ command.
• When a write error occurred on the restart data set (RDS) during checkpoint or restart (indicated by message DFS3127I).
• When you need to change the amount of space allocated to the WADS or a write error occurs on the WADS during normal operation. You should change the amount of space allocated to the WADS only after a controlled IMS shutdown. You can replace a WADS that encountered a write error during normal restart (/NRE) or emergency restart (/ERE). In any case, when IMS uses a new WADS, you must format it during restart.
• When read or write errors occur on one of the MSDB data sets during normal operation (indicated by messages DFS2718I or DFS2722I).

For other error situations that require reallocation and formatting of some or all of the system data sets, you must use the /ERE command.

During a warm start, IMS:

• Reestablishes the status of the control region using control blocks that were logged at termination
• Optionally restores local message queues if IMS logged them (you issued a /CHE DUMPQ | PURGE command)
• Restores in-doubt units of work so they can later be resolved

Unlike emergency restart, you might have to manually release any transactions on the suspend queue by:

• Re-executing the transaction by issuing a /START TRAN tranname command. This command releases a specific transaction.
• Issuing a /DEQUEUE SUSPEND command. This command releases all transactions on the suspend queue.

When using XRF with VTAM® Multinode Persistent Session (MNPS), IMS operates in an XRF environment and must use two ACBs: the APPLID ACB and the MNPS ACB. During a controlled shutdown, IMS closes the MNPS ACB and the APPLID ACB. Closing the MNPS ACB terminates MNPS tracking.

After a normal restart that follows this controlled shutdown, VTAM no longer maintains persistent sessions. Therefore, when IMS opens the MNPS ACB, it does not need to recover any previous sessions.