TQDBProxy

A high-performance MariaDB and PostgreSQL proxy with caching, read replica, metrics, and transaction support.

Blog post: https://www.tqdev.com/2026-tqdbproxy-mariadb-postgresql-proxy/

Features

• Query Caching: Cache SELECT queries with configurable TTL and thundering herd protection
• Caller Metadata: Track queries by source file and line number
• Metrics: Prometheus metrics for cache hits/misses, query latency, and more
• Read Replica Support: Automatic routing of SELECT queries to replicas
• Transaction Support: Full BEGIN/COMMIT/ROLLBACK support
• Interactive Mode: Full interactive client support

Performance

Cache hits are as fast as empty queries with 100 connections. Proxy overhead is minimal for queries ≥1ms.

Quick Start

# Start the proxy
./tqdbproxy

# Connect via MariaDB client (interactive mode)
mariadb -u tqdbproxy -p -P 3307 tqdbproxy --comments

Using Metadata Comments

Add caller metadata to your queries for better observability:

/* ttl:60 file:app.php line:42 */ SELECT * FROM users WHERE active = 1

NB: When using the MariaDB CLI, you must use the --comments flag to preserve metadata comments

Transaction Support

Full transaction support with proper isolation:

BEGIN;
UPDATE accounts SET balance = balance - 100 WHERE id = 1;
UPDATE accounts SET balance = balance + 100 WHERE id = 2;
COMMIT;

All query types supported:

• SELECT queries (with optional caching)
• INSERT queries (returns last insert ID)
• UPDATE queries (returns affected rows)
• DELETE queries (returns affected rows)

Query Status Inspection

Check which backend served the last query:

MariaDB:

mariadb> SHOW TQDB STATUS;
+---------------+---------+
| Variable_name | Value   |
+---------------+---------+
| Backend       | primary |
| Cache_hit     | 0       |
+---------------+---------+

PostgreSQL:

tqdbproxy=> SELECT * FROM pg_tqdb_status;
 variable_name |  value  
---------------+---------
 Backend       | primary
 Cache_hit     | 0
(2 rows)

Values: Backend = primary, replicaN, cache, or none (no query yet); Cache_hit = 0 or 1.

This is useful for debugging cache behavior during development.

Read Replicas

Configure replicas in config.ini:

[mariadb]
listen = :3307
primary = 127.0.0.1:3306
replica1 = 127.0.0.2:3306
replica2 = 127.0.0.3:3306

Select queries with a TTL hint are round-robin distributed across replicas.

Thundering Herd Protection

The proxy implements single-flight for warmup and resfresh to prevent concurrent DB queries for the same key.

Metrics

Access Prometheus metrics at http://localhost:9090/metrics:

curl http://localhost:9090/metrics | grep tqdbproxy_query_total

Metrics include file and line labels when metadata comments are used.

Cluster Setup

DNS round-robin load balancing can be used to distribute queries across multiple proxies.

Documentation

See docs/README.md for more information.