IMS transaction types and transaction states
Transactions are the most common type of data that is sent from a logical unit to IMS.
IMS supports two kinds of transactions—update and inquiry.
- An update transaction can modify a database.
- An inquiry transaction can look at data in a database, but it cannot change or update it.
You define transactions as update or inquiry during IMS system definition.
An additional attribute is defined for inquiry transactions—recoverable or irrecoverable.
- Recoverable-inquiry transactions are always recoverable, regardless of which element in the network fails.
- Irrecoverable-inquiry transactions are not recovered after an I/O error condition occurs or at IMS system restart.
All update transactions are recoverable. All Fast Path transactions must be defined as recoverable, but they can be either inquiry or update.
An LU 6.2 transaction is recoverable only if the asynchronous protocol is used to initiate the transaction. IMS conversational transactions from LU 6.2 programs are not recoverable in the local system, but they are recoverable across the MSC link.
IMS treats an irrecoverable transaction in the same manner as a recoverable transaction, except that all processing that required to achieve recoverability is eliminated. As a result, irrecoverable transactions require less processing time, but they could be lost in the event of a network failure (for example, line failure, CPC failure, or queue failure).
Transactions created for queuing only by the Destination Creation exit routine (DFSINSX0) have a status of DYN. The only purpose of a queue-only transaction is to queue a message to the shared queues. Queue-only transactions are not recovered at restart, unless they are stopped, or were not yet checkpointed.