It is very long and confusing. Here is my understanding of what happened even though I was not around for all of it.

0.1 - 0.20 was mostly main line development.  At that point there was a split and 0.20 was forked to add security, 0.20-security, and also to add in append support for H-BASE 0.20-append.  For a long time these branches were maintained and has bug fixes added to it while main line development went on with 0.21 and 0.22.  0.20-security was merged with 0.20-append and was renamed 1.0.  It has continued with bug fixes and some new feature work back ported from trunk.

But development did not stop at 0.22.  0.23 was created to support YARN/MR-V2.  At about the same time 0.24 was made for trunk.  When 0.20-security+append became 1.0, 0.23 became 2.0 and 0.24 became 3.0.  We at Yahoo! Have been in the process of stabilizing YARN for about a year or so.  Because 2.0 looked like new features were going to continue to go in we decided to keep 0.23 alive for stabilization purposes while 2.0 continued on.  It has since gotten several new features like HDFS-HA and protocol buffer based RPC for HDFS, and a few new features for YARN/MR.  So you can almost think of 0.23 as 2.0--.  We hope to move to 2.0 in the near future once it stabilizes and loses the alpha tag, at which point 0.23 would go away.

--Bobby Evans

From: Glen Mazza <gmazza@talend.com>
Reply-To: "user@hadoop.apache.org" <user@hadoop.apache.org>
Date: Friday, January 4, 2013 10:30 AM
To: "user@hadoop.apache.org" <user@hadoop.apache.org>
Subject: Re: Instructions on how to run Apache Hadoop 2.0.2-alpha?

OK, looking at the Hadoop branches: http://svn.apache.org/viewvc/hadoop/common/branches/ and tags: http://svn.apache.org/viewvc/hadoop/common/tags/, it's thankfully not that bad. 
There is no 0.24 in Hadoop, and the Maven pom files for the 2.0.2-alpha branch indeed say 2.0.2-alpha.  The Cloudera article linked to below mentions 0.24, but it's from 2011 and may have been at a time before the Hadoop team decided to relabel to 2.0 instead.  Looking at this again: http://hadoop.apache.org/docs/r2.0.2-alpha/hadoop-yarn/hadoop-yarn-site/SingleCluster.html, it appears to provide workable instructions, I'll try again with it.  Thanks for your assistance.

Glen

On 01/04/2013 11:17 AM, Chen He wrote:
Hi Glen

I agree with you. There are many versions and confusing. If you really want to know, you can check the developing and publishing documents. In 0.23's document, they must announced how many patches are included, as well as the 2.0.x.

Then you will exactly understand which one is which one.

Chen

On Fri, Jan 4, 2013 at 6:58 AM, Glen Mazza <gmazza@talend.com> wrote:
Thanks for your response.  That's pretty vital information--I'm not used to separate development/publication versions.  Is the 0.23-->2.0.2 renumbering stated anywhere on the Hadoop website or wiki?  It's very confusing as people otherwise think there are three separate branches -- 0.2x.y, 1.x, and 2.x when there are really just two. 

Also the releases page: http://hadoop.apache.org/releases.html mentions *both* 0.23.x and 2.0.2 releases -- wouldn't the former be numbered as the latter, if as you're saying, 0.23 is published as 2.0.x?

Thanks,
Glen


On 01/04/2013 07:02 AM, Chen He wrote:
0.24 is the developing version, 2.0.2 is the publication version.

0.23 or above is published as 2.0.x

On Fri, Jan 4, 2013 at 5:45 AM, Glen Mazza <gmazza@talend.com> wrote:
Actually, those instructions are for Hadoop 0.24, not 2.0.2-alpha.

Glen


On 11/30/2012 03:40 PM, Cristian Cira wrote:
Dear Glen,

try http://blog.cloudera.com/blog/2011/11/building-and-deploying-mr2/

Cristian Cira
Graduate Research Assistant
Parallel Architecture and System Laboratory(PASL)
Shelby Center 2105
Auburn University, AL 36849

________________________________________
From: Glen Mazza [gmazza@talend.com]
Sent: Friday, November 30, 2012 2:37 PM
To: user@hadoop.apache.org
Subject: Instructions on how to run Apache Hadoop 2.0.2-alpha?

Hi, I was able to run Hadoop 1.0.4 single-node with no difficulty following these instructions:  http://hadoop.apache.org/docs/stable/single_node_setup.html .

The corresponding page that we're referred to at the bottom of here: http://hadoop.apache.org/docs/current/ for Hadoop 2.0.2 is radically different, however, it doesn't seem to have anything to do with starting Hadoop:  http://hadoop.apache.org/docs/current/hadoop-yarn/hadoop-yarn-site/SingleCluster.html .  Is it because I'm looking at the wrong page or is it that Hadoop 2.0.2 is really so different that the instructions have radically changed?  Is there anything similar to http://hadoop.apache.org/docs/stable/single_node_setup.html that will show me how to run Hadoop 2.0.2?

Thanks,
Glen

--
Glen Mazza
Talend Community Coders - coders.talend.com
blog: www.jroller.com/gmazza<http://www.jroller.com/gmazza>




--
Glen Mazza
Talend Community Coders - coders.talend.com
blog: www.jroller.com/gmazza




-- 
Glen Mazza
Talend Community Coders - coders.talend.com
blog: www.jroller.com/gmazza



-- 
Glen Mazza
Talend Community Coders - coders.talend.com
blog: www.jroller.com/gmazza