Memo for logical replication code reading

Replication side

As of 12.5

• Boot flow
  • logical replication launcher assign a subscription to a slot (set slot as main arg)
  • bgworker launch logical replication apply worker

Logical replication launcher

Entry point

• list subscriptions
• launch logical replication worker
  Wait if replication slot is not available.

Logical replication apply worker

Entry point Note : this entry point is used for both replication apply worker and table synchronization worker.

Bootstrap

• Launch replication apply worker
  • Get replication origin (RepOriginId)
  • Connect to publisher
  • Start streaming
  • Enter main loop

Main loop

Receive WAL and process based on (Replication Protocol)

• Process messages until the buffer will be empty (inner loop)
  • “XLogData (B)”
    • apply dispatch
  • “Primary keepalive message (B)”
    • send feedback Send “Standby status update (F)”
• send_feedback
• reread subscription and process syncing tables if not in remote transaction
  • Process all tables that are being synchronized
    • Launch a table synchronization worker