Robustness Against Read Committed: A Free Transactional Lunch

Abstract

Transaction processing is a central part of most database applications. While serializability remains the gold standard for desirable transactional semantics, many database systems offer improved transaction throughput at the expense of introducing potential anomalies through the choice of a lower isolation level. Transactions are often not arbitrary but are constrained by a set of transaction programs defined at the application level (as is the case for TPC-C for instance), implying that not every potential anomaly can effectively be realized. The question central to this paper is the following: when - within the context of specific transaction programs - do isolation levels weaker than serializability, provide the same guarantees as serializability? We refer to the latter as the robustness problem. This paper surveys recent results on robustness testing against (multiversion) read committed focusing on complete rather than sufficient conditions. We show how to lift robustness testing to transaction templates as well as to programs to increase practical applicability. We discuss open questions and highlight promising directions for future research.