Abstract: Techniques for query execution against relational databases using connection pooling are described. According to some embodiments, a query processing service is disclosed that enables users to execute queries against target relational databases implemented by a relational database service. The service receives query requests originated by a client application at a web service endpoint and identifies a connection to a particular target database. In some examples, the query request is a Hyper Text Transfer Protocol (HTTP) message comprising a query to be executed by a target database instance within the provider network. The service transmits the query for execution at the target database via the connection and obtains a query result based on the execution of the query. The service transforms the query result into a format suitable for the client and transmits a query response to the client.