setup.sh

#!/usr/bin/env bash
# Primary + streaming replica on PostgreSQL 19beta3, in Docker.
# Primary on localhost:55432, replica on localhost:55433.
set -euo pipefail

IMG=${IMG:-postgres:19beta3}
NET=wf-net
PRIMARY=wf-primary
REPLICA=wf-replica
VOL=wf-replica-data

# The entrypoint runs a temporary unix-socket-only server during initdb, so
# pg_isready inside the container goes true too early. Wait on the TCP port
# instead: it only opens once the real server starts.
wait_tcp() {
  local port=$1
  for _ in $(seq 1 60); do
    PGPASSWORD=postgres psql -h localhost -p "$port" -U postgres -Atqc 'SELECT 1' \
      >/dev/null 2>&1 && return 0
    sleep 1
  done
  echo "server on port $port never came up" >&2; exit 1
}

docker rm -f "$PRIMARY" "$REPLICA" >/dev/null 2>&1 || true
docker volume rm "$VOL" >/dev/null 2>&1 || true
docker network create "$NET" >/dev/null 2>&1 || true

echo "== primary"
docker run -d --name "$PRIMARY" --network "$NET" \
  -e POSTGRES_PASSWORD=postgres -p 55432:5432 "$IMG" \
  -c wal_level=replica -c max_wal_senders=10 -c hot_standby=on \
  -c shared_buffers=256MB >/dev/null
# NB: nothing durability-related is passed on the command line. Command-line
# options outrank postgresql.auto.conf, so a `-c synchronous_commit=...` here
# would silently defeat every later ALTER SYSTEM in the experiments.

wait_tcp 55432

docker exec "$PRIMARY" psql -U postgres -q -c \
  "CREATE ROLE repl WITH REPLICATION LOGIN PASSWORD 'repl';"
docker exec "$PRIMARY" bash -c \
  "echo 'host replication all all scram-sha-256' >> \$PGDATA/pg_hba.conf"
docker exec "$PRIMARY" psql -U postgres -q -c "SELECT pg_reload_conf();" >/dev/null

echo "== base backup"
docker run --rm --network "$NET" -v "$VOL":/pgdata -e PGPASSWORD=repl "$IMG" \
  bash -c "pg_basebackup -h $PRIMARY -U repl -D /pgdata -R -X stream -c fast \
           && chown -R 999:999 /pgdata && chmod 700 /pgdata" >/dev/null

echo "== replica"
docker run -d --name "$REPLICA" --network "$NET" \
  -v "$VOL":/var/lib/postgresql/19/docker -p 55433:5432 "$IMG" >/dev/null

wait_tcp 55433

echo "== schema"
docker exec "$PRIMARY" psql -U postgres -q -c "
  CREATE TABLE messages (
    id     bigint GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
    author text NOT NULL,
    body   text NOT NULL,
    posted timestamptz NOT NULL DEFAULT now()
  );"

docker exec "$REPLICA" psql -U postgres -Atc "SELECT pg_is_in_recovery();" | \
  grep -qx t && echo "replica in recovery: ok"
docker exec "$PRIMARY" psql -U postgres -Atc \
  "SELECT application_name, state, sync_state FROM pg_stat_replication;"