In this blog post, we will explore how to utilize read and write replicas with Peewee, a lightweight Python ORM. Replicas allow us to distribute the load of read and write operations across multiple database servers, improving both performance and scalability.

What are Read & Write Replicas?

Read replicas are database servers that are used exclusively for performing read operations, such as SELECT queries. These replicas are synchronized with the primary database server for data consistency.

Write replicas are database servers that handle write operations, such as INSERT, UPDATE, and DELETE queries. These replicas are responsible for maintaining data consistency by replicating changes made to the primary server.

Setting Up Peewee with Replicas

To begin, make sure you have the latest version of Peewee installed:

pip install peewee

Next, let’s define the database connections for the primary and replica servers:

from peewee import *

# Primary database connection
primary_db = PostgresqlDatabase('primary_db', user='username', password='password', host='primary_host')

# Replica database connection
replica_db = PostgresqlDatabase('replica_db', user='username', password='password', host='replica_host')

Configuring Replicas in Peewee

Now, we need to configure Peewee to use replicas for read and write operations. Let’s create a custom Peewee database class that handles replication:

class ReplicatedDatabase(Proxy):
    def __init__(self):
        super().__init__()

        self.primary = primary_db
        self.replica = replica_db

        self.read_ds = [self.replica]  # List of replica connections
        self.write_ds = [self.primary]  # List of write connections

    def get_read(self):
        return random.choice(self.read_ds)  # Randomly select a replica for each read operation

    def get_write(self):
        return random.choice(self.write_ds)  # Randomly select a primary server for each write operation

# Create an instance of the ReplicatedDatabase class
database = ReplicatedDatabase()

Using Replicas in Queries

With the replicas configured, we can now use them in our Peewee queries:

class User(Model):
    name = CharField()
    email = CharField()
    ...

    class Meta:
        database = database  # Use the replicated database instance

# Select query using read replica
users = User.select().where(User.name == 'John').using(database.get_read())

# Insert query using write replica
new_user = User.create(name='Alex', email='alex@example.com').using(database.get_write())

Monitoring and Managing Replicas

Peewee provides methods for monitoring and managing replicas. For example, you can use the database.check_connections() method to check the availability of replica servers.

database.check_connections()

Additionally, you can dynamically add or remove replicas from the self.read_ds list based on the current server load or other factors.

Conclusion

In this blog post, we explored how to leverage read and write replicas with Peewee, allowing us to distribute the load of database operations and improve performance and scalability. By configuring the replicas and using them in our queries, we can achieve better utilization of resources and maintain data consistency.

Peewee’s support for replicas makes it a powerful tool for working with large-scale applications that require efficient database management. Consider incorporating replicas into your Peewee project to optimize your application’s performance.