Servers that do not support two-phase commit

In a distributed transaction, Db2 can coordinate a mixture of two-phase and one-phase connections.

You cannot have coordinated updates with a DBMS that does not implement two-phase commit. You can, however, achieve the effect of coordinated updates when you access a server that does not implement two-phase commit; such a server is called a restricted system.

Db2 prevents you from updating both a restricted system and any other system in the same unit of work. In this context, update includes the statements INSERT, DELETE, UPDATE, CREATE, ALTER, DROP, GRANT, REVOKE, and RENAME.

You can achieve the effect of coordinated updates with a restricted system. You must first update one system and commit that work, and then update the second system and commit its work. However, suppose that a failure occurs after the first update is committed and before the second update is committed. No automatic provision is available to bring the two systems back to a consistent point. Your program must handle that task.

When you access a mixture of systems, some of which might be restricted, you can take the following actions to ensure data integrity:

• Read from any of the systems at any time.
• Update any one system many times in one unit of work.
• Update many systems, including CICS® or IMS, in one unit of work if no system is a restricted system. If the first system you update is not restricted, any attempt to update a restricted system within a unit of work results in an error.
• Update one restricted system in a unit of work. You can do this action only if you do not try to update any other system in the same unit of work. If the first system that you update is restricted, any attempt to update another system within that unit of work results in an error.