> 1. Is it possible that the tool needs to be applied the other way around, that is having 0.22 as the base and Tested version being 0.21?
The method signature changed, which is reported as the method being removed. In 0.21 it was
protected SequenceFile.Reader createDataFileReader(FileSystem fs,
Path dataFile, Configuration conf)
And in 0.22 it is
createDataFileReader(Path dataFile, Configuration conf,
> 2. Did you run the tool against MR only? Hard to believe there were no API changes in HDFS and common.
I ran it against all three. HDFS is marked as @Private, so it won't show up in the report.
> 3. What is the final goal of this jira. Is it to identify incompatible changes and make a patch for site with the release notes?
Yes, including it in the release notes would be a good start.
> If so we can filter out non public changes from the reports generated by SigTest and probably those that do not belong to public APIs in turns of Hadoop annotations, if it makes sense.
The script already uses the annotations to restrict the changes to the public API.