Commit-time ordered message queue supporting arbitrary read and dequeue patterns from multiple subscribers

A computer-implemented method, comprising:

• in response to a request, from a client of a database system, to enqueue one or more first messages, the database system adding said one or more first messages to a message queue, said one or more first messages associated with a first database transaction being executed for said client,
• after adding said one or more first messages to the message queue:
• committing the first database transaction;
• and
• determining a unique system commit time corresponding to the first database transaction, wherein system commit times corresponding to respective database transactions are based on transactional dependencies among database transactions;
• after determining a unique system commit time:
• associating the unique system commit time with the one or more first messages;
• and
• ordering messages in the message queue based on the unique system commit time;
• in response to a request to dequeue one or more messages from the message queue,
• determining whether any message of the one or more messages is associated with a system commit time that is less than a first high watermark that is associated with the message queue;
• and
• if there are no messages, of the one or more messages, that are associated with a system commit time that is less than the first high watermark, then generating a second high watermark for association with the message queue, wherein the second high watermark is greater than the first high watermark,
• wherein the method steps are performed by one or more computing devices.