As noted previously, one of the reasons for reporting topology update data is resource state changes. Of the state changes that occur for resources, many of the resulting states are transient in nature. That is, the resource is in transition from one state to another, but the transition is through a series of intermediate states. These intermediate states are usually brief and are considered less important than the resting states.

Because the number of updates reporting transient state changes can be large, the VTAM topology agent suppresses the intermediate updates. This process is called merging, because the intermediate updates are merged instead of discarded.

luCollection updates for independent LUs in a snapshot directed at a specific PU are not merged. snaNetwork updates for APPN network data are not merged.

Updates for resources moving to transient states are merged until an update is received that shows the resource moving to a resting state. The resting state update is merged, and the final, merged update is sent.

It is possible for resources to stay in transient states too long; for example, when an error occurs and a resource is hung in a state that is not a resting state. The VTAM topology agent periodically looks for updates that have been held too long; when these are found, they are sent.

The UPDDELAY start option controls the maximum length of time that VTAM® waits before looking for resource updates that have been in transient states too long. This start option specifies the maximum number of seconds to wait before looking for resources that are hung. Note that decreasing the value for UPDDELAY might force VTAM to look for these resources more often, but does not necessarily imply that resources are reported any faster. The time specified in the UPDDELAY start option does not affect the computing of whether a resource has stayed in a transient state too long. That computing is not controllable and is based primarily on recent updates statistics.

Although a given type of snapshot update is eligible to be merged, in some cases, individual updates are not merged.

EVENT-REPORT data is also subject to the merge process.

By design, the merge process suppresses intermediate state data; however, there is one case where the loss of intermediate state data is not acceptable. The availabilityStatus attribute reports the value of dependency when a higher-level resource is in transition. When updates are merged, the newest state data generally replaces the older state data, but for the dependency information this is not the case. The VTAM topology agent preserves the dependency information from all updates that are merged to a single update by performing the logical OR operation on the dependency information from all updates. The result is that if any of the set of merged updates have the dependency flag set for a resource, the reported (merged) update reports the dependency in the availabilityStatus attribute.