This setting controls the size of the batch of messages that is returned from the HTTP send adapter. The default value for this is 5. If the buffer is not full and there are outstanding responses then the adapter will wait for 1 second until it commits the batch. For low-latency scenarios this should be set to 1 which will allow the adapter to send response messages immediately to the message box for processing. This will have the greatest effect during times of low-throughput activity with varied response times from backend systems.
Actually this setting controls the number of messages being returned to BizTalk (EPM) from the HTTP adapter regardless of whether the port is one-way or two-way. A message that is returned in the batch includes a request to DeleteMessage, MoveToNextTransport, MoveToSuspendedQ, and, most interestingly, SubmitResponseMessage. Although this setting will improve response times in low-latency scenarios it does increase the amount of chattiness between the adapter and the message box.
It is the send side equivalent to the HttpBatchSize on an HTTP receive adapter. In low-latency scenarios this is typically set to 1 to ensure that the messages are getting processed as quickly as they are received.
To set this value you need to add HttpOutCompleteSize as a DWORD value to the registry under:
where GUID is the ID of the host for HTTP send handler.
This information is specific to BizTalk Server 2004 and there is no guarantee that this setting will behave the same way in the next release of BizTalk Server.
Disclaimer: This is an undocumented setting and was not formally tested since it was not considered to be publicly available. You must do your own testing to ensure that the behavior and performance of your system are as expected.