Piql: Success-tolerant query processing in the cloud

Newly-released web applications often succumb to a “Success Dis-aster, ” where overloaded database machines and resulting high re-sponse times destroy a previously good user experience. Unfortu-nately, the data independence provided by a traditional relational database system, while useful for agile development, only exac-erbates the problem by hiding potentially expensive queries under simple declarative expressions. As a result, developers of these applications are increasingly abandoning relational databases in fa-vor of imperative code written against distributed key/value stores, losing the many benefits of data independence in the process. In-stead, we propose PIQL, a declarative language that also provides scale independence by calculating an upper bound on the number of key/value store operations that will be performed for any query. Coupled with a service level objective (SLO) compliance predic-tion model and PIQL’s scalable database architecture, these bounds make it easy for developers to write success-tolerant applications that support an arbitrarily large number of users while still provid-ing acceptable performance. In this paper, we present the PIQL query processing system and evaluate its scale independence on hundreds of machines using two benchmarks, TPC-W and SCADr. 1