Publish/subscribe: changes to how the subscription selection string is evaluated

In this release, message selection for publish/subscribe messaging is made on the message as sent by the publisher, rather than on the message as eventually received by the subscriber.

For subscriptions with a SelectionString, the string is now evaluated against the message as put by the publisher before it is modified for delivery to each subscriber.

This change in behavior might affect subscribers with selection strings that reference fields that are modified during the publish operation. For example:
  • The MQMD fields UserIdentifier, MsgId, CorrelId
  • Message properties such as UserData.