Hadoop 0.23.0 Alpha Release (first with YARN)

This was the very first pre-release of Hadoop 2.x that included YARN, then referred to as 'MapReduce 2.0'. It was a developer-focused preview, allowing early adopters and contributors to experiment with the new architecture.

Significance

Marked the official public debut of YARN's code, signalling a massive architectural shift for the Hadoop project and inviting community collaboration on its development.