FIFO ordering across queue consumers
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Key: AMQ-1684
URL: https://issues.apache.org/activemq/browse/AMQ-1684
Project: ActiveMQ
Issue Type: New Feature
Components: Broker
Environment: problem is not environment specific
Reporter: Michael Ingardia
The JMS spec is silent on how messages are distributed across queue consumers
when there is more than one consumer on the same queue. In many cases where
processing of a given task is highly dependent upon the order they are
processed ( requires FIFO processing ), a JMS queue is often used with a single
consumer that is singled theaded. Although this does achieve FIFO processing
it leaves handling the failure of the consumer up to the programmer which is a
difficult task. Some JMS providers provide a way to specify that a message
will not be delivered to a queue consumer (receive will block ) while a message
taken from that destination has not been commited. What this allows for is to
have multiple queue consumers hanging off of one queue but only one of the
consumers can process a message at any given time. If one of the consumer
processes is killed then the message is not commited, a time out occurs and the
message is rolled back to the queue and the next consumer get the message and
continues on its merry way. This makes writting a fault tolerant system much
easier as you can spread consumers of a queue across multiple machines etc.
Today ActiveMQ does not seem to support this capability, if more than one
consumer pulls from the same queue the messages are load balanced across the
consumers but there is no way to block a consumer from getting the next message
thus if consumer A gets message 1, and one takes 10 seconds to process and
consumer B gets message 2 immediately and it only takes 1 second to process 2,
will beat one and cause down stream out of order problems. Handling this at
the broker centrally is a much better solution than trying to come up with some
distributed locking system that the consumers have to implement.
My proposal is to add a feature to the Queue that allows for only one out
standing message transaction, and blocks all receivers until the message is
either commited or rolled back..
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