pgvector-repl/
├─ docker-compose.yml
├─ primary/
│  └─ init/
│     └─ 01_init.sql
├─ replica/
│  └─ bootstrap.sh
└─ demo.py

version: "3.9"

services:
  primary:
    image: pgvector/pgvector:pg16
    container_name: pg_primary
    environment:
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: postgres
      POSTGRES_DB: vectordb
    ports:
      - "5432:5432"
    volumes:
      - primary-data:/var/lib/postgresql/data
      - ./primary/init:/docker-entrypoint-initdb.d
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U postgres -d vectordb"]
      interval: 3s
      timeout: 3s
      retries: 30

  replica:
    image: pgvector/pgvector:pg16
    container_name: pg_replica
    depends_on:
      primary:
        condition: service_healthy
    environment:
      POSTGRES_PASSWORD: postgres
    ports:
      - "5433:5432"
    volumes:
      - replica-data:/var/lib/postgresql/data
      - ./replica/bootstrap.sh:/usr/local/bin/bootstrap.sh
    entrypoint: ["/bin/bash", "-c", "/usr/local/bin/bootstrap.sh"]
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U postgres -d vectordb -h localhost -p 5432"]
      interval: 3s
      timeout: 3s
      retries: 30

volumes:
  primary-data:
  replica-data:

-- Postgres 16 + pgvector + streaming replication

-- 1) Replication settings
ALTER SYSTEM SET wal_level = 'replica';
ALTER SYSTEM SET max_wal_senders = 10;
ALTER SYSTEM SET max_replication_slots = 10;
ALTER SYSTEM SET wal_keep_size = '256MB';

-- 2) Replication user
DO $$
BEGIN
  IF NOT EXISTS (SELECT 1 FROM pg_roles WHERE rolname = 'replicator') THEN
    CREATE ROLE replicator WITH REPLICATION LOGIN PASSWORD 'replpass';
  END IF;
END$$;

-- 3) Enable adminpack to modify pg_hba.conf
CREATE EXTENSION IF NOT EXISTS adminpack;

-- 4) Allow replication from Docker subnet
SELECT pg_file_write(
  'pg_hba.conf',
  E'\n# --- Allow replication from Docker bridge network ---\n' ||
  E'host replication replicator 172.18.0.0/16 md5\n' ||
  E'host all         all        0.0.0.0/0     md5\n',
  TRUE
);

-- 5) Enable pgvector and create demo table
CREATE EXTENSION IF NOT EXISTS vector;

DROP TABLE IF EXISTS items;
CREATE TABLE items (
  id serial PRIMARY KEY,
  embedding vector(3),
  note text
);

-- 6) Reload config and create replication slot
SELECT pg_reload_conf();

DO $$
BEGIN
  IF NOT EXISTS (SELECT 1 FROM pg_replication_slots WHERE slot_name='replica1') THEN
    PERFORM pg_create_physical_replication_slot('replica1');
  END IF;
END$$;

#!/usr/bin/env bash
set -euo pipefail

PRIMARY_HOST="primary"
PRIMARY_PORT="5432"
REPL_USER="replicator"
REPL_PASS="replpass"
DATA_DIR="/var/lib/postgresql/data"

echo "Waiting for primary to be ready..."
until pg_isready -h "$PRIMARY_HOST" -p "$PRIMARY_PORT" -U postgres >/dev/null 2>&1; do
  sleep 1
done

if [ -s "$DATA_DIR/PG_VERSION" ]; then
  echo "Replica already initialized."
  exec docker-entrypoint.sh postgres
fi

echo "Cloning base backup..."
export PGPASSWORD="$REPL_PASS"
rm -rf "$DATA_DIR"
gosu postgres pg_basebackup \
  -h "$PRIMARY_HOST" -p "$PRIMARY_PORT" \
  -U "$REPL_USER" -D "$DATA_DIR" -Fp -Xs -P -R

cat >> "$DATA_DIR/postgresql.auto.conf" <<EOF
primary_conninfo = 'host=$PRIMARY_HOST port=$PRIMARY_PORT user=$REPL_USER password=$REPL_PASS application_name=replica1'
primary_slot_name = 'replica1'
EOF

exec docker-entrypoint.sh postgres

chmod +x replica/bootstrap.sh

import time
import psycopg2

PRIMARY_DSN = "host=localhost port=5432 dbname=vectordb user=postgres password=postgres"
REPLICA_DSN = "host=localhost port=5433 dbname=vectordb user=postgres password=postgres"

emb = [0.12, 0.34, 0.56]
note = "Inserted on primary; watch it appear on replica."

with psycopg2.connect(PRIMARY_DSN) as conn:
    conn.autocommit = True
    with conn.cursor() as cur:
        cur.execute("CREATE EXTENSION IF NOT EXISTS vector;")
        cur.execute("INSERT INTO items (embedding, note) VALUES (%s, %s) RETURNING id;", (emb, note))
        row_id = cur.fetchone()[0]
        print(f"Inserted id={row_id} into primary.")

deadline = time.time() + 20
while time.time() < deadline:
    with psycopg2.connect(REPLICA_DSN) as conn:
        with conn.cursor() as cur:
            cur.execute("SELECT id, embedding::text, note FROM items WHERE id = %s;", (row_id,))
            r = cur.fetchone()
            if r:
                print("Replica has it:", r)
                break
    time.sleep(1)

pip install psycopg2-binary
docker compose up -d
python demo.py

Inserted id=1 into primary.
Replica has it: (1, '[0.12,0.34,0.56]', 'Inserted on primary; watch it appear on replica.')

docker exec -it pg_replica psql -U postgres -d vectordb \
  -c "SELECT status, sent_lsn, write_lsn, flush_lsn, replay_lsn FROM pg_stat_wal_receiver;"