# Application-level read routing with SQLAlchemy
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

# Two engine pools
primary_engine = create_engine("postgresql://primary_host/db", pool_size=20)
replica_engine = create_engine("postgresql://replica_host/db", pool_size=50)

def get_write_session():
    """Always use primary for writes"""
    Session = sessionmaker(bind=primary_engine)
    return Session()

def get_read_session():
    """Use replica for reads"""
    Session = sessionmaker(bind=replica_engine)
    return Session()

# Usage:
def get_user(user_id: int):
    with get_read_session() as session:
        return session.query(User).get(user_id)

def create_order(data: dict):
    with get_write_session() as session:
        order = Order(**data)
        session.add(order)
        session.commit()

Database Replication — Master-Slave, Multi-Master

Database Replication — Master-Slave, Multi-Master

Database Replication — Master-Slave, Multi-Master