Read Replicas — Scaling Reads

Architecture Intermediate

Read Replicas — Scaling Reads¶

Read ReplicasDatabaseScaling 3 min read

Scaling databases with read replicas. Master-slave replication and routing.

Principle¶

80-90% of operations are reads. Read replicas distribute read load across copies of the master DB.

Application Routing¶

const master = new Pool({ host: 'master-db' });
const replica = new Pool({ host: 'replica-db' });

class Database {
    async query(sql, params, opts = {}) {
        const pool = opts.readOnly ? replica : master;
        return pool.query(sql, params);
    }
}
await db.query('INSERT INTO orders ...', [data]);  // → master
await db.query('SELECT * FROM orders', [], { readOnly: true });  // → replica

Summary¶

The simplest way to scale reads. Watch out for replication lag — critical reads after writes should go to the master.

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