Distributed support

Remote unit of work is where the preparation and running of SQL statements occurs at only one application server during a unit of work. An activation group with an application process at an application requester can connect to an application server and, within one or more units of work, run any number of static or dynamic SQL statements that refer to objects on the application server. Remote unit of work is also referred to as DRDA level 1.

Distributed unit of work is where the preparation and running of SQL statements can occur at multiple applications servers during a unit of work. However, a single SQL statement can only refer to objects located at a single application server. Distributed unit of work is also referred to as DRDA level 2.

Distributed unit of work allows:

• Update access to multiple application servers in one logical unit of work

  or

• Update access to a single application server with read access to multiple application servers, in one logical unit of work.

Whether multiple application servers can be updated in a unit of work is dependent on the existence of a sync point manager at the application requester, sync point managers at the application servers, and two-phase commit protocol support between the application requester and the application servers.

The sync point manager is a system component that coordinates commit and rollback operations among the participants in the two-phase commit protocol. When running distributed updates, the sync point managers on the different systems cooperate to ensure that resources reach a consistent state. The protocols and flows used by sync point managers are also referred to as two-phase commit protocols. If two-phase commit protocols will be used, the connection is a protected resource; otherwise the connection is an unprotected resource.