Messaging Wishlist

[derekperkins]

I'm hoping to do some significant messaging work in Q2 and this is a list of various features that exist in other queueing systems that would be great if they were supported in Vitess.

• Allow INSERT INTO msg_table SELECT col1, col2... (added in messaging: simplified -> Breaking Change #5948)
• Allow filtered topic subscriptions messages: support topic/subscriber filter policies #5180 - this builds on the prior task and should work once vreplication supports filters (vreplication support added in Filtered Vreplication: support int and varbinary filters for columns #5949)
• Always include a json meta column - this allows for future meta improvements without breaking compatibility messager: add special support for time_expires, min/maxBackoff #5415
• Merge those meta keys with arbitrary user key value pairs - see SQS https://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/sqs-message-attributes.html
• Add backoff jitter see https://aws.amazon.com/blogs/architecture/exponential-backoff-and-jitter/ (added in messager: add 33% jitter to postpone backoff #6092)
• Support min/max backoff - rather than doubling forever, provide bounds (added in messaging: support min/max backoff #5979)
• Support priority queues: add an optional priority column (tinyint) (added in messaging: add new priority field #5967)
  https://github.com/bgadrian/data-structures/tree/master/priorityqueue
  https://www.rabbitmq.com/priority.html
• Allow for storing message errors/status that aren't delivered to consumers - see Google Cloud Tasks https://godoc.org/google.golang.org/genproto/googleapis/cloud/tasks/v2#Task
  To be implemented with stream col1, col2 from msg_table instead of only stream * from msg_table
• Use vreplication for topics - the current implementation of topics is brittle and only supports same-tablet subscribers
  Explicit topic support was removed in schema: simpler and faster schema load #5951. For now this can be done easily with vreplication on a single topic table. If there becomes a need for explicit topic support in Vitess, we can revisit in the future
• Support message lease extension - related to messaging: duplicate message delivery #5796, this lets smart clients extend the deadline for messages they have received and intend to process
  https://cloud.google.com/pubsub/docs/reference/rest/v1/projects.subscriptions/modifyAckDeadline
  As discussed on Slack, this can be done today with UPDATE time_next = NOW()
• Explicit nacks - today the only way for a message to be redelivered is to wait for the message timeout. By allowing for nacks on failure, you can avoid unnecessary delays.
  As discussed on Slack, this can be done today with UPDATE time_next = NOW()
• Support message state field - Possibly related to the prior item, this would enable new states like "failed". Today, this can be modeled by setting time_next to a very large number.
  Also discussed on Slack and deemed to be unnecessary