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It is also assumed that the events to be delivered atomically must be so by means of the same gateway sender. Therefore, the deployments that require this feature should configure replication such that the regions to which the data in the transactions belong must be collocated and must have the same gateway sendersenders. Additionally, if serial gateway senders are used, they must be configured with just one dispatcher thread given that it would be impossible to fulfill the requirement if each event of a transaction is handled by a different dispatcher thread.

Solution

In order for the gateway senders to deliver batches that contain all the events for the transactions the following is proposed:

• After transaction commit and before events are sent to the gateway sender, mark the last event of the transaction (a new boolean attribute “lastEventInTransaction” may be added to GatewaySenderEventImpl)
  
• In the process of creating a batch, the gateway sender must keep track of all the transactions involved in the events it is putting in the batch.
• Once a batch is due to be sent (due to maximum configured size is reached or time), the gateway sender must check:
  • If  for every transaction to which events on the batch belong, the last event has been received, then the batch may be sent.
  • Otherwise, two options are proposed:
    • a) Keep reading events from the queue and put them in the batch until the above condition is fulfilled. Then send the batch. This option has the problem that the size of batches could grow a lot beyond the maximum size in situations of big transactions and high number of them.
    • b) Go to the queue and get selectively the events for the transactions in the batch that do not have all the events. Once these events are added to the batch, send it. This option is preferred over option a) because it should avoid the problem of batches much bigger than the maximum size configured.

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