Optimise send message route.

[insertish]

Sending messages is the most common and important route to optimize at this point in time.

Database queries in order of execution:

• Fetch session.
• Fetch user.
• Fetch channel and determine permissions.
  • (if server) fetch server.
  • (if server) fetch member.
• Check if message is a duplicate.
• (if replies > 0) Fetch each message.
• (if attachments > 0):
  • Fetch each attachment.
  • Update each attachment.
• Insert message.
• Update channels (last_message_id).
• Update channel unreads.
• (if embeds) Update message.
• (if web push) Find all sessions.

Efficiency problems:

• Worst case: 23 database queries
• Average case for Revolt general: 8 database queries

Issue resolution:

• [ ] Write psuedo-code for new pipeline.
• [ ] Implement session cache, map session token to user ids in memory.
  • [x] https://github.com/insertish/rauth/issues/29
• [x] #106
• [x] #108
• [ ] Fetch all reply-to messages at once. (low priority)
• [ ] Fetch all attachments at once. (low priority)
• [x] Send event immediately after validation, commit to database afterwards.
• [x] #107
• Create task queues.
  • [x] #110
  • [x] #111
  • [x] #112
  • [x] #113

[insertish]

Closing in favour of https://github.com/revoltchat/backend/issues/174.