Hi Faye,
please have a look at the following article:
http://techcommunity.softwareag.com/pwiki/-/wiki/Main/setting+correct+trigger+parameters
This has an overview how to configure triggers for different scenarios.
Setting the trigger to serial (1 thread is default and not changeable) is the correct setting for clusters.
The main goal you are looking for is to delay the acknowledgement of the documents until IS has finished the processing for the document.
One option might be to do a publishAndWait in the service invoked by the trigger to another service and the publish a response back after processing is finished. When the first service receives the response and completes its execution the document will be acked to UM marking the next one as available for retrieval.
Maybe other members have other ideas.
Regards,
Holger
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