Problem

If the primary path to a data source fails to open there is a requirement to be able to specify an alternative path and for that path to be accessed automatically in the event of such a failure. The explicit use of ‘open’ proc statements provides a partial solution to this problem. However, the ability to specify at a configuration level one or more alternative paths would be useful.

Solution

Path-to-driver assignments can be used to define a sequence of fallback paths to be used to reach the required information. If the initial path fails to open UNIFACE tries to open the first alternative path specified. If the first alternative path also fails to open UNIFACE tries to open the second alternative path.

Example of Usage

A read only database located on a server in Birmingham is accessed via a UNIFACE application to provide management information. If the database in Birmingham becomes inaccessible then a duplicate/standby database located on a server in Manchester should be accessed instead. If the database in Manchester becomes inaccessible then another duplicate/standby database located on a server in Bristol should be used.

Method

In the following example, two alternative paths are provided for the path $DEF;

[PATHS]

$DEF = TCP:birm|kaye|parrot

$DEF[1] = TCP:manc|kaye|?

$DEF[2] = TCP:bris|emu|general|?

If the logon to node ‘birm’ does not succeed, UNIFACE will try to open the fallback path to ‘manc’. A log on form will be presented for user ‘kaye’ on node ‘manc’. If the user cannot log on to ‘manc’ or clicks on ‘Cancel’, UNIFACE tries to open the second alternative path namely, to node ‘bris’.

The alternative paths must be numbered sequentially, beginning with 1, and there must not be any gaps in the sequence. No errors are reported if these rules are not followed. There is no limit to the number of alternative paths that can be specified.

Please note that it is only valid to use the path fallback mechanism in path-to-driver assignments. The target cannot be another path.

Note

This facility is supported from UNIFACE Seven version 7.2.02 onwards.

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