Write Amplification
Jae-Myung Kim, Kenneth Salem, Khuzaima Daudjee · 2015
Modern in-memory database systems perform transactions an order of magnitude faster than conventional database systems. While in-memory database systems can read the database without I/O, database updates can generate a substantial amount of I/O, since updates must normally be written to persistent secondary storage to ensure that they are durable. In this paper we present a study of storage managers for in-memory database systems, with the goal of characterizing their I/O efficiency. We model the storage efficiency of two classes of storage managers: those that perform in-place updates in secondary storage, and those that use copy-on-write. Our models allow us to make meaningful, quantitative comparisons of storage managers' I/O efficiencies under a variety of conditions.