Watermark-based message queue

A system comprising:

• data processing apparatus;
• and
• memory hardware in communication with the data processing apparatus, the memory hardware storing instructions that when executed on the data processing apparatus cause the data processing apparatus to perform operations comprising:
• receiving, from a user device, a first connection request for messages associated with the user device;
• identifying a message queue of messages associated with the user device, wherein each message in the message queue is associated with a respective timestamp;
• establishing a first connection session with the user device;
• identifying a current watermark that is associated with i) the message queue and ii) the first connection session, the current watermark identifying a previous timestamp of an oldest message remaining in the message queue at a start of a previous connection session preceding the first connection request, the previous connection session terminated prior to the first connection request;
• providing, to the user device, one or more messages that have a timestamp newer than or equal to the previous timestamp identified by the current watermark in response to the first connection request during the first connection session;
• receiving user input from the user device, the user input identifying a unit of time;
• in response to receiving the user input, updating the current watermark according to the unit of time;
• and
• deleting messages that have been in the message queue for a time period longer than or equal to unit of time associated with the current watermark.

A computer program product, encoded on one or more non-transitory computer storage media, comprising instructions that when executed by one or more computers cause the one or more computers to perform operations comprising:

• receiving, from a user device, a first connection request for messages associated with the user device;
• identifying a message queue of messages associated with the user device, wherein each message in the message queue is associated with a respective timestamp;
• establishing a first connection session with the user device;
• identifying a current watermark that is associated with i) the message queue and ii) the first connection session, the current watermark identifying a previous timestamp of an oldest message remaining in the message queue at a start of a previous connection session preceding the first connection request, the previous connection session terminated prior to the first connection request;
• providing, to the user device, one or more messages that have a timestamp newer than or equal to the previous timestamp identified by the current watermark in response to the first connection request during the first connection session;
• receiving user input from the user device, the user input identifying a unit of time;
• in response to receiving the user input, updating the current watermark according to the unit of time;
• and
• deleting messages that have been in the message queue for a time period longer than or equal to unit of time associated with the current watermark.