SQL Relay is a persistent database connection pooling, proxying, and load balancing system. It supports many database systems and programming languages. There are drop-in replacement libraries for MySQL and PostgreSQL, command line clients, a GUI configuration tool, and extensive documentation. The APIs support advanced database operations such as binding variables, multi-row fetches, client-side result set caching, suspended transactions, query routing, and query filtering. It can be used for speeding up database-driven Web-based applications, accessing databases from unsupported platforms, migrating between databases, distributing access to replicated databases, and throttling database access.