I recently came across Hadoop version, in this I noticed that, both 2.6.5 and 2.7.3 are been developed parallel and simultaneous.If possible someone please give me difference between them.
08 October, 2016: Release 2.6.5 available A point release for the 2.6 line. Please see the Hadoop 2.6.5 Release Notes for the list of 79 critical bug fixes and since the previous release 2.6.4.
25 August, 2016: Release 2.7.3 available A point release for the 2.7 line. Please see the Hadoop 2.7.3 Release Notes for the list of 221 bug fixes and patches since the previous release 2.7.2.
http://hadoop.apache.org/releases.html explains the difference between the 2.6 and 2.7 releases:
21 April 2015: Release 2.7.0 available
Apache Hadoop 2.7.0 contains a number of significant enhancements. A few of them are noted below.
IMPORTANT notes
This release drops support for JDK6 runtime and works with JDK 7+ only.
So the difference is that 2.7 was introduced for JDK 7+, but 2.6 continues having releases to support JDK6 users.
From that same link you can see that 2.7 is having more bug fixes made per point release than the 2.6 tree.