Target ID Handling in the Network

This document covers the following topics:

(Global) Target IDs Must Be Unique

Entire Net-Work normally enforces unique global target IDs throughout the network, that is, across all connected nodes. Unless both targets are local, a target is not permitted to start if another target with the same ID is active anywhere in the network. The ADAM98 message (Target Initialization Error) will result.

When a link is established between two previously unconnected partial networks, it is possible that the same target ID is used in both parts simultaneously. Because target IDs must be unique within the network, this is considered an error situation. Entire Net-Work cannot determine which of the targets should be deactivated. Therefore the link between the two parts of the network is not established and explanatory messages (NET0108 and NET0106) are written to the operator consoles of both the nodes trying to connect. It is the responsibility of the installation to terminate one of the conflicting targets. The link can then be connected from either side by using the CONNECT LINK operator command.

Duplicate Target IDs Restricted to LOCAL Node

Adabas provides a feature that permits the use of duplicate target IDs under special circumstances. A target ID can be used on all nodes in the network simultaneously if all targets with that ID are declared LOCAL (see the Adabas Operations Manual for the appropriate ADARUN parameter). In this case, any one of the targets with that ID can be accessed only by users running on the same node.

Entire Net-Work does not transport requests to LOCAL targets. The RSP148 message is generated if a user program calls a target declared LOCAL from a remote node.

A target ID cannot be used simultaneously for both a local target and a global target. The reason for this restriction is illustrated in the following example.

Imagine that a (global) database, DBID 35, is active on node PROD, and user programs from all nodes in the network are issuing calls to it. If a local database, also with DBID 35, starts on node TEST, it immediately draws all calls that originate on node TEST to the local database DBID 35. Users on other nodes are not affected, but all users on node TEST are switched in mid-transaction from the global database DBID 35 to the local database DBID 35, a different and probably totally unrelated database. This error situation cannot be permitted.

Entire Net-Work enforces this rule and thus prevents the confusion that would result if a local target ID coincided with a global target ID by broadcasting information about local targets to all nodes the same way it does for global targets.