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Replica Component

The replica component manages multiple backend pools, each containing a primary database and optional read replicas. It provides the core sharding and routing logic for the proxy.

Features

  • Multi-Pool Management: Supports multiple named backend pools as defined in the hierarchical configuration.
  • Database Sharding: Maps specific databases to different backend pools for horizontal scaling.
  • Load Balancing: Implements a Round-Robin strategy within each pool to distribute read queries across healthy replicas.
  • Health Checks: Periodically verifies the availability of all primary and replica backends using TCP or Unix connection probes.
  • Automatic Failover: Transparently falls back to the primary database within a pool if no healthy replicas are available.

Routing Logic

  • Shard Routing: Determines the correct backend pool based on the database name (at connection time for PostgreSQL, or dynamically for MariaDB).
  • Primary: All write operations (INSERT, UPDATE, DELETE) and non-cacheable SELECTs are routed to the pool's primary.
  • Replicas: Cacheable SELECT queries (those with a ttl > 0 hint) are distributed across healthy replicas in the pool.

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