Over the last few years there has been an increasing interest in immutable data management. This is a big change from the traditional update-in-place approach many database systems use today, where new values delete old values, which are then lost. With immutable data you record everything, generally using methods that append data from successive transactions rather than replacing them.  In some DBMS types you can access the older values, while in others the system transparently uses the old values to solve useful problems like implementing eventual consistency.

Baron Schwartz recently pointed out that it can be hard to get decent transaction processing performance based on append-only methods like append-only B-trees.  This is not a very strong argument against immutable data per se. …

Like a lot of developers I started using a MacBook Pro around the time of Tiger.  I instantly loved it:  simple, fast, and virtually no system administration overhead. The genius of OS X was that it never got in the way. You opened the box, pulled out the machine, and got to work. It had a great user interface, excellent  development tools (Eclipse in my case) and the command utilities like ssh, rsync, and bash worked seamlessly with Linux systems.

Well, that was then and this is now. Starting with Lion I began to spend an increasing amount of time fighting OS X instead of getting work done. I'm now using Mavericks and have not seen much improvement, in fact quite the contrary. Here are just a few of the problems after the Lion to Mavericks upgrade:

• Spotlight indexes destroyed; need 2 days to regenerate
• AppleMail access to Gmail IMAP  broken
• Time Machine stuck in …

Anders Karlsson wrote about Some myths on Open Source, the way I see it a few days ago.  Anders' article is mostly focused on exploding the idea that open source magically creates high quality code.  It is sad to say you do not have to look very far to see how true this is.

While I largely agree with Anders' points, there is far more that could be said on this subject, especially on the benefits of open source. I love working on open source software. Here are three reasons that are especially important to me.

1.) Open source is a great way to disseminate technology to users.  In the best cases, it is this easy to get open source products up and running:

$ sudo apt-get install software-i-want-to-use

A lot of software companies ( …

There have been a number of excellent articles about the pros and cons of automatic database failover triggered by Baron's post on the GitHub database outage.  In the spirit of Peter Zaitsev's article "The Math of Automated Failover," it seems like a good time to point out that database failure is usually not the biggest source of downtime for websites or indeed applications in general.  The real culprit is maintenance.

Here is a simple table showing availability numbers out to 5 nines and what they mean in terms of monthly down-time.

Github had a recent outage due to malfunctioning automatic MySQL failover.  Having worked on this problem for several years I felt sympathy but not much need to comment.  Then Baron Schwartz wrote a short post entitled "Is automated failover the root of all evil?"  OK, that seems worth a comment:  it's not.  Great title, though.

Selecting automated database failover involves a trade-off between keeping your site up 24x7 and making things worse by having software do the thinking when humans are not around.  When comparing outcomes of wetware vs. software it is worth remembering that humans are not at their best when woken up at 3:30am.  Humans go on vacations, or their cell phones run out of power. …

In late 2011 I attended a lecture by John Wilkes on Google compute clusters, which link thousands of commodity computers into huge task processing systems.  At this scale hardware faults are common.  Google puts a lot of effort into making failures harmless by managing hardware efficiently and using fault-tolerant application programming models.  This is not just good for application up-time.  It also allows Google to operate on cheaper hardware with higher failure rates, hence offers a competitive advantage in data center operation.

It's becoming apparent we all have to think like Google to run applications successfully in the cloud.  At Continuent we run our IT and an increasing amount of QA and development on Amazon Web Services …

The MySQL UC this past week was the best in years.   Percona did an outstanding job of organizing the main Percona Live event that ran Tuesday through Thursday.  About 1000 people attended, which is up from the 800 or so at the O'Reilly-run conference in 2011.  There were also excellent follow-on events on Friday for MariaDB/SkySQL, Drizzle, and Sphinx.

What made this conference different was the renewed energy around MySQL and the number of companies using it.  

1. Big web properties like Facebook, Twitter, Google, and Craigslist continue to anchor the …

Since the famous conjecture by Eric Brewer and proof by Nancy Lynch et al., CAP has given the world countless learned discussions about distributed systems and many a well-funded start-up.  Yet who truly understands what CAP means?  Even a cursory survey of the blogosphere shows profound disagreement about the meaning of terms like CP, AP, and CA in real systems.  Those who disagree on CAP include some of the most illustrious personages of the database community.

We can therefore state with some confidence that CAP is confusing. Yet this observation itself raises deeper questions.  Is CAP merely confusing?  Or is it the case that as with other initially accepted but now doubtful ideas like the Copernican …

MySQL community conferences are alive and well in 2012.   Percona has taken the initiative to host the yearly MySQL event at the Santa Clara Hyatt; it's now called Percona Live MySQL Conference and Expo.  It runs from 10 through 12 April.  But don't plan on going home Thursday night.  On Friday 13 April you can also attend the SkySQL and MariaDB MySQL Solutions Day in the same location.  And wait, that's not all!  Drizzle Day is also on 13 April and also at the Hyatt, so you can catch up on what the Drizzle folks have been up to for the last 12 months.

Now for some specifics on the conferences where Continuent will be appearing. …

If you are interested in NoSQL databases (or maybe not) perhaps you have seen the anonymous "warning" about using MongoDB.   It concludes with the following pious request:

  Please take this warning seriously.

Now there are a lot of great resources about data management on the web but the aforementioned rant is not one of them.  If you plan to write technical articles and have people take them seriously, here are a few tips.

1. Sign your name.  Readers are more impressed when they see you are not afraid to stand behind your words. 
2. Explain what problem you were trying to solve.  Otherwise uncharitable readers might think you just started pumping information into a new database without thinking about possible consequences and now want to blame somebody …