Compiling PL/SQL Away

TL;DR

This paper introduces a method to compile PL/SQL functions into SQL queries, significantly improving performance by eliminating interpretation overhead and enabling efficient evaluation within the database engine.

Contribution

It presents a novel compilation technique that transforms arbitrary PL/SQL functions into SQL subqueries, including recursive control flow, for faster execution.

Findings

Significant runtime improvements across various RDBMSs

Effective compilation of complex control flow including recursion

Challenging traditional developer assumptions about PL/SQL performance

Abstract

"PL/SQL functions are slow," is common developer wisdom that derives from the tension between set-oriented SQL evaluation and statement-by-statement PL/SQL interpretation. We pursue the radical approach of compiling PL/SQL away, turning interpreted functions into regular subqueries that can then be efficiently evaluated together with their embracing SQL query, avoiding any PL/SQL to SQL context switches. Input PL/SQL functions may exhibit arbitrary control flow. Iteration, in particular, is compiled into SQL-level recursion. RDBMSs across the board reward this compilation effort with significant run time savings that render established developer lore questionable.