VerIso: Verifiable Isolation Guarantees for Database Transactions

Abstract: Isolation bugs, stemming especially from design-level defects, have been repeatedly found in carefully designed and extensively tested production databases over decades. In parallel, various frameworks for modeling database transactions and reasoning about their isolation guarantees have been developed. What is missing however is a mathematically rigorous and systematic framework with tool support for formally verifying a wide range of such guarantees for all possible system behaviors. We present the first such framework, VerIso, developed within the theorem prover Isabelle/HOL. To showcase its use in verification, we model the strict two-phase locking concurrency control protocol and verify that it provides strict serializability isolation guarantee. Moreover, we show how VerIso helps identify isolation bugs during protocol design. We derive new counterexamples for the TAPIR protocol from failed attempts to prove its claimed strict serializability. In particular, we show that it violates a much weaker isolation level, namely, atomic visibility.