Jenkins

Jenkins is an open source, web-based build automation server. It's worth a mention here as it's built in Java. It was created in 2006 and initially named "Hudson" by a developer at SUN called Kohsuke Kawaguchi. When Oracle bought SUN in 2009, there was a dispute over trademarks and the project continued under the banner of Jenkins.

Jenkins can be used for technology stacks other than Java. For example, MSBuild is supported via dedicated plugin. There is also an Android emulator plugin.

A book, "Jenkins: The Definitive Guide" has been published in 2001 and written by Sydney-based IT consultant John Ferguson Smart.

HDFS In Numbers

Hadoop makes use of the Hadoop File System, or HDFS, a distributed file system. It differs from other distributed file systems in that it is specifically designed for:

1) Large data sets (in the sense that each file is gigabytes or terabytes in size)
2) Implementation on low cost hardware (so cheaply scalable to hundreds or thousands of machines)

Each server machine can store part of the file system's data.

A more detailed introduction on HDFS' design can be found here.

The Hadoop API is detailed here.