sequence.md

Sequence

It's the mechanism for storing queue-id updates history. When you send any message like this to queue:

POST http://localhost:8081/queue/send/test
Host: localhost:8081
Content-Type: application/json

{
  "id": "1",
  "payload": {
    "message": "hello"
  }
}

All messages getting sequence_id. sequence_id - it is a local id that starts with 1 and atomically increments on every sent message with the same queue and id.

sequence_id will return on subscribe responses in message body.

With the sequence_id you can receive missed updates of your key.

GET http://localhost:8081/queue/listen/longpoll/test?sequence={sequence_id} will return the message with set sequence_id. If a message with set sequence_id does not exist, the method will wait for the next sent message.

Also, sequence_id may accept first and last value. It's return to you first and last key versions from api.

Long poll without data lost example:

Java Script

let sequence_id = 1;
while (true) {
    const response = await fetch('http://localhost:8081/queue/listen/longpoll/test?sequence=' + sequence_id)
    const data = await response.json()
    sequence_id = data.sequence + 1
}

Custom sequence_id

You can replace auto-generated sequence_id to own realization. Just set your sequence to message body on sending.

POST http://localhost:8081/queue/send/test
Host: localhost:8081
Content-Type: application/json

{
  "id": "1",
  "sequence": 999,
  "payload": {
    "message": "hello"
  }
}

Configure history size

You can set the maximum message versions for storing on config file or env.

queue:
  max_key_updates: 10

The default value is null, the queue will not remove historical versions of messages. Set max_key_updates to 0 and message versions will not store anymore.

When the max_key_updates value is more than 0, every update of the message will clean old message versions if the count of all message versions is more than max_key_updates.

Example:

If we set max_key_updates to 1. The only previous version with the max sequence_id will be stored.