Micro-Specialization in DBMSes

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 micro-specialization, 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.