Problem

-- several processing engines are defined for the HME

-- the max number of messages configured in the HME is the default value : 5

-- most of the processing messages are small (several kb) and are processed in few seconds, but there are also larger messages (several MB) that may take several minutes to be processed

-- when a "large" message is being processed, it happens that several messages (less than 5) are being stuck until the large message is processed

Resolution

* most of the time, the incoming messages are well distributed among the different processing engines, which means that if a large message is picked-up by a PE, this PE will be busy, and the smaller messages will be processed by the other PEs

* but it may happen that a PE picks-up several messages at the same time, and if there is a larger file among the bunch of messages, this larger files can be processed before the smaller messages, and it ends up getting smaller messages "stuck" in the queue until the larger message is processed

* that is the normal behavior because the max number of messages set in the HME is 5

* a possible solution to avoid this behavior is to set the max number of messages to 1. Be aware that it might have an impact on the performance, so proceed to performance tests bafore applying such kind of changes to the production environment