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Transactions: Myths, Surprises and Opportunities

A talk at Code Mesh, London, UK, 04 Nov 2015

This was a repeat of my talk at Strange Loop 2015.


Back in the 1970s, the earliest databases had transactions. Then NoSQL abolished them. And now, perhaps, they are making a comeback… but reinvented.

The purpose of transactions is to make application code simpler, by reducing the amount of failure handling you need to do yourself. However, they have also gained a reputation for being slow and unscalable. With the traditional implementation of serializable transactions (2-phase locking), that reputation was somewhat deserved.

In the last few years, there has been a resurgence of interest in transaction algorithms that perform well and scale well. This talk answers some of the biggest questions about the bright new landscape of transactions:

  • You know that ACID stands for Atomicity, Consistency, Isolation and Durability, but are you certain that you know precisely what those words mean? What race conditions can you get with weak isolation (such as “read committed” and “repeatable read”), and how does this affect your application?
  • How do modern implementations of serializability work, and how are they different from traditional algorithms?
  • What are the strongest guarantees we can achieve, while maintaining high availability and high performance at scale?
  • When you build a microservices architecture or use stream processing, you often end up with data spread across multiple databases. Does this mean you inevitably have to give up transactional guarantees?


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