Last august, I started wanting a new API for MySQL Cluster that could solve a few problems. Frist, if you were to use MySQL Cluster in a LAMP application, you would be turning a two-layer architecture (Apache and MySQL) into three layers (Apache, MySQL, and NDB). Adding that extra tier requires more hardware and means slower response times. Second, the one way around this was to write native NDB API code in C++, but learning the API and developing low-level code can require a big commitment of time. I wanted an easier way to eliminate the extra layer.

My solution is called mod_ndb, and it is an Apache module that runs inside a web server and connects directly to the MySQL Cluster data nodes. It supports a “RESTful” API — applications make GET, POST, and DELETE requests over HTTP, and mod_ndb provides appropriate HTTP responses. Because it is HTTP, responses can be cached by proxies in a well-defined way, and data can be delivered “straight from the database to the browser” in an AJAX application.

The code is now available at http://code.google.com/p/mod-ndb, with documentation hosted on the MySQL Forge Wiki at http://forge.mysql.com/wiki/Mod_ndb.

While I don’t have lots of performance measurements, the benchmarks so far show that if you simply replace a mysqld with an httpd and query it using HTTP instead of SQL, mod_ndb has performance very similar to or slightly better than mysql. (However, you have to use persistent HTTP, so that if you are making five queries you can make them all in one TCP connection, rather than five). And if mod_ndb allows you to improve the overall architecture, a very big performance improvement can be gained — maybe even a factor of ten.

The current release is not quite beta: some HTTP response codes need to be corrected, along with some formatting details of particular data types. Also, for now, mod_ndb can provide output either in JSON or in a simple XML format, but the big improvement I hope to make before the MySQL Conference next month is to support user-defined output formats. I’ll be presenting mod_ndb at the conference on Tuesday, April 24th at 5:30 PM.