I've just created a new branch, 0.89. It has the current state of our largest HBase deploy, Facebook Messaging. 0.89 was branched from HBase trunk back in 2010 before the release of HBase 0.90.0 so its pretty old. The current HBase trunk has most of whats in 0.89 (and more) except for some bug fixes and testing/operation tools. Our intention is to have this branch closely mirror the code that we currently run in production, to provide the community visibility on how we iterate on a branch that serves production, and to serve as a transition point to be more transparent with our production development & porting status. We do most active development on this branch, but we've started moving internal development onto 0.92 & are putting more resources into stabilizing that.
Q. Should I look into using this 0.89 branch?
I would discourage it unless you know what you're doing. The average developer will get far highly quality assistance with 0.90 or 0.92 issues. 0.89 is a transitory branch who's main purpose is to move towards 0.90+. This is also about enhancing the transparency for members of the community that are still using 0.89 and making minor fixes/improvements to it.
Q. Will there be a release candidate of this branch?
There are no current plans to make any official release candidate for this branch.
Q. Why an Apache branch? Why not just tell Facebook to put what they have on GitHub?
1. Aligning the 0.89 & 0.92 efforts under Apache will accelerate contributing 0.89 master features to the new master on trunk, allow the community to port 0.89 features at a pace that they think is important, and give developers an idea of development history on merge conflicts.
2. Facebook would like to get its developers in the habit of actively using the Apache workflow utilities like JIRA & Review Board instead of internal utilities for their day-to-day HBase operations. We wish to promote transparency and want to find some way for Facebook to improve on this goal as well.