Improving Predictability of Transaction Execution Times in Real-time Databases

Abstract

We present a design for multi-versionconcurrency control and recovery in a main memory database, anddescribe logical and physical versioning schemes that allowread-only transactions to execute without obtaining data itemlocks or system latches. Our schemes enable a system to providethe guarantee that updaters will never interfere with read-onlytransactions, and read-only transactions will not be delayeddue to data contention. Consequently, transaction executionsbecome more predictable—this partially alleviates a majorproblem in real-time database system (RTDBS) scheduling, namely,significant unpredictability in transaction execution times.As a result, in addition to a transaction's deadline, a moreaccurate estimate of its execution time can also be taken intoaccount, thus facilitating better scheduling decisions. Our contributionsinclude several space saving techniques for the main-memory implementation,including improved methods for logical aging of data items andthe introduction of physical aging for low-level structures.Some of these schemes have been implemented on a widely-usedsoftware platform within Lucent, and the full scheme is implementedin the Dalí main-memory storage manager.