PAQO: A preferenceaware query optimizer for postgreSQL

Although the declarative nature of SQL provides great util-ity to database users, its use in distributed database manage-ment systems can leave users unaware of which servers in the system are evaluating portions of their queries. By allowing users to merely say what data they are interested in access-ing without providing guidance regarding how to retrieve it, query optimizers can generate plans with unintended conse-quences to the user (e.g., violating user privacy by revealing sensitive portions of a user's query to untrusted servers, or impacting result freshness by pulling data from stale data stores). To address these types of issues, we have created a framework that empowers users with the ability to specify constraints on the kinds of plans that can be produced by the optimizer to evaluate their queries. Such constraints are specified through an extended version of SQL that we have developed which we call PASQL. With this proposal, we aim to demonstrate PAQO, a version of PostgreSQL's query op-timizer that we have modified to produce plans that respect constraints specified through PASQL while optimizing user-specified SQL queries in terms of performance.