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From Allen Wittenauer ...@altiscale.com>
Subject Re: fsck output compatibility question with regard to HDFS-7281
Date Fri, 24 Apr 2015 08:02:43 GMT

On Apr 24, 2015, at 5:53 AM, Yongjun Zhang <yzhang@cloudera.com> wrote:

> 
> Basically we are adding two additional lines to the report (as highlighted
> above).
> 
> Theoretically if a tool parses existing fsck report and expects the
> 'Corrupt blocks" entry to be right after the "Average block replication"
> entry, then the change would fail the tool. But is this really a concern?
> 
> I guess this is not really a concern, so I don't think this change is
> incompatible. but would anyone please comment?
> 

	If it changes the output of a CLI command, it's an incompatible change:

	http://hadoop.apache.org/docs/r2.7.0/hadoop-project-dist/hadoop-common/Compatibility.html#Command_Line_Interface_CLI


	Other changes to fsck have been punted to 3.x for the *exact same reason*. In other cases,
committers have violated these rules in branch-2 (not just to fsck, but to all sorts of other
command line bits, even removing command options!) to the point that our compatibility guarantees
are pretty much useless.  It's open season on nuking the ecosystem. :(

	People not following the compat rules is one of the reasons I started building my own changes
and release notes, because we have too many committers either accidentally committing incompatible
changes or just outright lying about them.  (… and, as much as I hate to say it, the HDFS
project is easily the biggest offender.)
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