Advanced Query Routing
Protocol-aware regex-based routing to primary, replicas, or shards.
Architectural Value
Query rules allow for a truly "Database-as-a-Service" experience. You can route traffic based on users, schemas, or the query content itself without changing a single line of application code.
Key Capabilities
- → Read/Write Splitting: Automatically send SELECTs to replicas and INSERT/UPDATEs to primaries.
- → Query Rewriting: Fix problematic queries on-the-fly or add SQL hints.
- → Traffic Sharding: Route queries to different database shards based on key values.
Architectural Review
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Schedule a Call →The Problem
Applications don’t issue uniform traffic. A single service generates reads, writes, analytical queries, and bulk operations — each with different latency requirements, resource costs, and appropriate destinations. But the application itself has no awareness of your database topology. It holds a connection string pointing at one endpoint and trusts the database layer to handle everything. That works when you have one server. It breaks down the moment you introduce replicas, read pools, or horizontal sharding.
The conventional fix is to modify the application: introduce separate connection strings for reads and writes, add routing logic in the ORM, or build service-layer abstractions that are aware of your topology. This couples your application code to your infrastructure decisions. Every topology change — adding a replica, introducing a shard, promoting a standby — requires application changes, redeployment, and coordination across teams.
The ProxySQL Approach
ProxySQL evaluates every query against an ordered ruleset before it touches a backend. Rules match on any combination of username, schema, client IP, and the query text itself via regex. The first matching rule determines where the query goes — which host group, which backend pool, and with what modifications. The application sees a single endpoint and remains entirely unaware of what happens next.
This is what makes a genuine Database-as-a-Service experience possible. The routing layer is owned and operated by the infrastructure team, independently of the application. Topology changes are absorbed at the proxy layer with zero application involvement.
What You Can Do With It
Read/Write Splitting is the most common use case. ProxySQL matches SELECT statements and routes them to a replica host group, while writes go to the primary. Replicas absorb the read load that would otherwise accumulate on your primary, extending its effective capacity without schema changes or application rewrites.
Query Rewriting allows ProxySQL to intercept a query and modify it before execution. Missing index hints, suboptimal query patterns from third-party ORMs, or queries that need a SQL_NO_CACHE directive applied — these can all be corrected at the proxy layer without touching application code or waiting for a deployment cycle.
Traffic Sharding routes queries to different backend clusters based on values extracted from the query itself. A regex match on a tenant ID, account range, or key prefix determines which shard receives the query. ProxySQL becomes the routing layer for a sharded architecture without requiring the application to implement any sharding logic.
The Result
Query routing at the proxy layer decouples your database topology from your application entirely. Your read replicas get utilized systematically rather than speculatively. Your primary handles only what it must. Problematic queries are corrected without redeployment. And as your architecture evolves — more replicas, sharding, regional distribution — the application never changes. Only the routing rules do.