Different commit-ids in github across releases

[Rajat Jain <ra...@gmail.com>]

I notice that each hadoop release-tag in github
<https://github.com/apache/hadoop> (for example, release-2.5.0 tag and
release-2.5.1 tag) have different commit-ids for the same commit (eg. this
<https://github.com/apache/hadoop/commit/029165bddea5853c27c6a76aa2a6643aea187503>
and this
<https://github.com/apache/hadoop/commit/128919856a0199c7bf20bef6fae6d0b22bbe69ad>).
I wanted to know if there is a reason behind having different commits-ids
for the same commit in different branches.

Specifically I'm asking this question because we fork the apache hadoop
github, and customize it for our use. Because the commit-ids are different
across releases, it is difficult to merge the latest releases into our
repo. We essentially have to cherry-pick our commits into each new release.

Any suggestions on how we can make our "merges" more efficient, or is there
a plan to streamline commits across releases?

Thanks,
Rajat