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 topic and filter, and deletes all messages that match the filter from the topic specified.

• 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. SOW keys are provided in the header of a SOW message, and are the internal identifier AMPS uses for that SOW message.

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

Most applications use sowDelete(), since this is the most useful and flexible method for removing items from the SOW. In some cases, particularly when working with extremely large SOW databases, sowDeleteByKeys() can provide better performance.

In either case, AMPS sends an OOF message to all subscribers who have received updates for the messages removed, as described in the previous section.

sowDelete() returns a Promise that resolves with a Message object. This Message is an acknowledgment that contains information on the delete command. For example, the following snippet simply prints informational text with the number of messages deleted:

const ack = await client.sowDelete('sow-topic', '/id IN (42, 37)');

console.log(
  'Got an',
  ack.header.command(), 'message containing',
  ack.header.ackType(), '-- deleted',
  ack.header.matches(), 'SOW entries'
);

// Got an ack message containing stats -- deleted 2 SOW entries

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.