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Subject: persistDuration and retries
The following point surfaced during today's CPPA F2F. Reliable messaging includes the following elements among others: persistDuration, Retries, RetryInterval. persistDuration defines the maximum time to allow for successfully retrying the sending of a message in the reliable messaging protocol. Retries defines the maximum number of retries that may be made for failure to receive a RM ACK. RetryInterval defines the time to wait before making a retry. A delivery failure is recognized if either persistDuration expires or the allowed number of retries has been used up. There is a bit of overdetermination going on here. There are three different maximum times: persistDuration Initial timeout + (Retries-1)XRetryInterval+timeout_of_last_retry if RetryInterval is longer than the timeout Initial timeout + RetriesXTimeout if the timeout is longer than RetryInterval. Note that the value of the timeout is not defined in either the message service spec or the CPP-CPA spec. It appears to be an implementation detail of the message service handler. In the message service specification, nothing appears to be said about the relationships among these times. It appears that a delivery failure is recognized when the first of these maximum times expires. Note that if persistDuration expires first, the message service handler will recognize a delivery failure although the timeout following the most recent retry may not have expired. The CPP-CPA specification is also silent on this overdetermination. Because timeout is not defined, the CPA tools cannot check consistency. It may be worthwhile to put a non-normative discussion of this in the CPP-CPA specification. We should be concerned about persistDuration potentially causing the timeout for the most recent retry to be truncated, however. Regards, Marty ************************************************************************************* Martin W. Sachs IBM T. J. Watson Research Center P. O. B. 704 Yorktown Hts, NY 10598 914-784-7287; IBM tie line 863-7287 Notes address: Martin W Sachs/Watson/IBM Internet address: mwsachs @ us.ibm.com *************************************************************************************
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