When an MQTT trigger receives a message from the MQTT server, the trigger places the message in a local trigger queue which is an internal memory-based queue on the Integration Server. The message remains in the local trigger queue until it is pulled from the queue for processing. The MQTT trigger processes messages in the same order in which the trigger retrieved the messages. When the local trigger queue is at capacity, the MQTT trigger cannot receive any new messages from the MQTT server. The MQTT trigger must process one or more messages in the queue before more messages can be retrieved.

The local trigger queue acts as a buffer between the receipt of the message and processing the message. One server thread handles message retrieval while a separate server thread handles message processing. When configuring message processing the intent is to size the queue and set concurrent execution threads such that there is a steady retrieval and processing of messages. The queue capacity and execution thread values need to minimize the resources that the local trigger queue and service execution consume, such as memory, as well as limit the situations where new messages cannot be received because the local trigger queue is full.