Database management systems (DBMSes) form a cornerstone of modern IT infrastructure, and it is essential that they have excellent performance. Much of the work to date on optimizing DBMS performance has emphasized ensuring efficient data access from secondary storage. This paper shows that DBMSes can also benefit significantly from dynamic code specialization. Our approach focuses on the iterative query evaluation loops typically used by such systems. Query evaluation involves extensive references to the relational schema, predicate values, and join types, which are all invariant during query evaluation, and thus are subject to dynamic value-based code specialization. We introduce three distinct types of specialization, each corresponding to a particular kind of invariant. We realize these techniques, in concert termed micro-specialization, via a DBMS-independent run-time environment and apply them to a highperformance open-source DBMS, PostgreSQL. We show that microspecialization requires minimal changes to the DBMS and can yield performance improvements simultaneously across a wide range of queries and modifications, in terms of storage, CPU usage, and I/O time of standard DBMS benchmarks. We also discuss an integrated development environment that helps DBMS developers apply micro-specializations to identified target code sequences. 1.

Abstract—Relational database management systems are general in the sense that they can handle arbitrary schemas, queries, and modifications; this generality is implemented using runtime metadata lookups and tests that ensure that control is channelled to the appropriate code in all cases. Unfortunately, these lookups and tests are carried out even when information is available that renders some of these operations superfluous, leading to unnecessary runtime overheads. This paper introduces microspecialization, an approach that uses relation- and query-specific information to specialize the DBMS code at runtime and thereby eliminate some of these overheads. We develop a taxonomy of approaches and specialization times and propose a general architecture that isolates most of the creation and execution of the specialized code sequences in a separate DBMS-independent module. Through three illustrative types of micro-specializations applied to PostgreSQL, we show that this approach requires minimal changes to a DBMS and can improve the performance simultaneously across a wide range of queries, modifications, and bulk-loading, in terms of storage, CPU usage, and I/O time of the TPC-H and TPC-C benchmarks. I.