IOPURGE start option

The setting of the IOPURGE start option specifies an interval after which outstanding I/O requests are purged. The types of I/O requests that are checked are:

CDINIT requests
Direct search list requests
APPN search requests
HPR route setup requests

For CDINIT requests, after the specified time interval, if a response has not been received, VTAM® continues its search through the adjacent SSCP table until it either finds the resource or the table has been exhausted. For the other requests, if IOPURGE expires, VTAM handles the request as if a negative response to the request has occurred.

If IOPURGE is set too low, outstanding searches will be terminated before normal searching has completed. This can result in failed searches and possibly increased network traffic because of retries. This can occur if IOPURGE on an end node or migration data host is set to a value that does not allow the network node server to complete all search tasks and return a reply.

If IOPURGE is set to 0, outstanding I/O requests can remain outstanding indefinitely.

Note: Do not use IOPURGE for congestion control. If you have APPN congestion control problems, use a lower MAXLOCAT value. IOPURGE was intended for situations where a node drops a request and never responds and not for congestion control.