docker-compose.yml

services:
  postgres:
    image: postgres:16
    # `-n auto` gives one xdist worker per core, each holding several connections, and more than
    # one worktree runs a suite against this container at a time. Measured on a 12-core machine:
    # one suite alone peaks at 105 concurrent connections and averages 68, against the postgres
    # default of 100. Over the ceiling the failure is a psycopg.OperationalError on connect, which
    # lands on whichever database-touching test was running -- so it moves between runs and reads
    # as a flaky test rather than as exhausted connections. Two of us lost hours to that today.
    command: ["postgres", "-c", "max_connections=300"]
    environment:
      POSTGRES_USER: sync
      POSTGRES_PASSWORD: sync
      POSTGRES_DB: sync
    ports:
      - "5433:5432"
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U sync"]
      interval: 2s
      timeout: 3s
      retries: 15