High Availability

20 years later, what's left of the CAP theorem?

The CAP theorem was published in (party like it's...) 1999: Fox Armando, Brewer Eric A: Harvest, Yield, and Scalable Tolerant Systems.

Since its publication it has provided a beacon and rallying cry around which web scale distributed databases could be built and debated. It(s interpretation) has also evolved. Quite quickly the original 1999 formulation was abandoned, and from there it has further eroded as real world database implementations have provided ever more finer grained trade offs for navigating the space that - after all - was correctly mapped out by the CAP theorem.

Pick ANY two? Really?

3 modifications to the Raft consensus algorithm (paper)

Update: This version of my paper is superceded by a new version: 4 modifications to Raft consensus. Please read it instead.

August is usually a slower month as a lot of people are on vacations. I try to take advantage of that to work on tasks that require a bit more deliberation and quiet time. This Summer I returned to re-reading the paper on the Raft algorithm, in particular my colleagues in New York pointed out that the PhD thesis that extends on the original paper was now complete, and contains some additional details.

Slides for Evaluating MySQL HA Alternatives

Attached are the slides for my MySQL Connect talk Evaluating MySQL High-availability alternatives, which I will present today at 14:30 at the MySQL Connect conference.

A bit unusually I'm posting the material ahead of the talk. The point of the talk is about evaluating each alternative from your own perspective. With that in mind, if you're at the talk with your own laptop, feel free to browse the slides at your own pace from here.

Failover is evil

In the Matrix movie there is a scene where the heroes visit a spiritual councelor, and amongst the people in her waiting room they see a little boy, dressed like a buddhist monk, who can bend a spoon just by looking at it. When they ask him what he does to bend the spoon, the boy's answer is: "There is no spoon". And if you watch the movie to the end, you will see that he is right. (In that spirit, if this post is too long to read for you, just skip to the last paragraph for the answer.)

The title for this blog post is of course inspired by Baron's "Is automated failover the root of all evil?", which is a commentary on GitHub's detailed explanation of their recent Pacemaker-induced downtime. Baron makes a good question, but the answer is deeper than suggested by the question. The problem is not the automation, the problem is the failover.

Helsinki MySQL User Group on May 29

The Helsinki MySQL User Group will meet at the usual place on May 29th. Click here for details and to RSVP. Linas Varbalas will talk about Tungsten and maybe dare a live demo!

Linas is in town for the OUGF Harmony conference 2012. The conference might of course be of some interest to user group members too. Due to the conference we also have other famous MySQLrs in town, Sheeri Kabral of OurSQLcast fame has also confirmed she will attend the user group (and maybe have OurSQLcast CD's with her?)

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