practice

TRANSACTIONS ARE AMAZINGLY powerful mechanisms, and I’ve spent the majority of my almost 40-year career working on them. In 1982, I first worked to provide transactions on the Tandem NonStop System. This system had a mean time between failures measured in years4 and included a geographically distributed two-phase commit offering excellent availability for strongly consistent transactions.

New innovations, including Google’s Spanner, 2 offer strongly consistent transactional environments at extremely large scale with excellent availability. Building distributed transactions to support highly available applications is a great challenge that has inspired excellent innovation and amazing technology. Unfortunately, this is not broadly available to application developers.

In most distributed transaction systems, the failure of a single node causes transaction commit to stall.

This in turn causes the application to get wedged. In such systems, the larger it gets, the more likely the system is going to be down. When flying an airplane that needs all of its engines to work, adding an engine reduces the availability of the airplane. Running a distributed transaction system over thousands of nodes is impractical without special mechanisms to tolerate outages. When application developers build systems using non-highly available distributed transactions, the solutions are brittle and must be discarded. Natural selection kicks in…

Instead, applications are built using techniques that do not provide transactional guarantees but still meet the needs of their business.

This article explores and names some of the practical approaches used in the implementation of large-scale mission-critical applications in a world that rejects distributed transactions. Topics include the management of fine-grained pieces of application data

Life Beyond
Distributed
Transactions
DOI: 10.1145/3009826

Article development led by queue.acm.org

An apostate’s opinion.
BY PAT HELLAND

This is an updated and abbreviated version of an article by the same name first published in Proceedings of the Conference on Innovative Database Research, 2007.