Managing SOW Contents

AMPS allows applications to manage the contents of the SOW by explicitly deleting messages that are no longer relevant. For example, if a particular delivery van is retired from service, the application can remove the record for the van by deleting the record for the van.

The client provides the following methods for deleting records from the SOW.

• sowDelete - Accepts a filter, and deletes all messages that match the filter.

• sowDeleteByKeys - Accepts a set of SOW keys as a comma-delimited string and deletes messages for those keys, regardless of the contents of the messages. A SOW key is provided in the header of a SOW message, and is the internal identifier AMPS uses for that SOW message.

• sowDeleteByData - Accepts a message, and deletes the record that would be updated by that message.

The most efficient way to remove messages from the SOW is to use sowDeleteByKeys or sowDeleteByData, since those options allow AMPS to exactly target the message or messages to be removed. Many applications use sowDelete, since this is the most flexible method for removing items from the SOW when the application does not have information on the exact messages to be removed.

Regardless of the command used, AMPS sends an OOF message to all subscribers who have received updates for the messages removed, as described in the previous section.

The simple form of the sowDelete command returns a MessageStream that receives the response. The response is an acknowledgment message that contains information on the delete command. For example, the following snippet simply prints informational text with the number of messages deleted:

for (Message msg : client.sowDelete("sow_topic", "/id IN (42, 64, 37)")) {
    System.out.println("Got an " + msg.getCommand() +
                      " containing " + msg.getAckType() + ": " +
                      " deleted " + msg.getMatches() + " messages.");
}

You can also use client.execute to send a SOW delete command. As with the other SOW methods, the client provides an asynchronous versions of the SOW delete commands that require a message handler to be invoked.

Acknowledging messages from a queue uses a form of the sow_delete command that is only supported for queues. Acknowledgment is discussed in the Using Queues chapter in this guide.