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When transmitting a large set of data, you might want to break it into message-size smaller chunks in order to maintain system performance. The Message Sequence EIP facilitates this by sending data as a message sequence of smaller messages and marking each message with sequence identification fields. For more information, refer to http://www.eaipatterns.com/MessageSequence.html.
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When the sent request is large, WSO2 ESB by default chunks breaks it into smaller sizeschunks. In order to maintain consistency of the message, each chunk is then mapped with a sequence identity number so that its sequential order is not lost.