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https://issues.apache.org/jira/browse/HBASE-25861?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17347293#comment-17347293
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Baiqiang Zhao commented on HBASE-25861:
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Thanks for the review [~ndimiduk] !
> Correct the usage of Configuration#addDeprecation
> -------------------------------------------------
>
> Key: HBASE-25861
> URL: https://issues.apache.org/jira/browse/HBASE-25861
> Project: HBase
> Issue Type: Bug
> Affects Versions: 3.0.0-alpha-1, 2.5.0
> Reporter: Baiqiang Zhao
> Assignee: Baiqiang Zhao
> Priority: Major
> Fix For: 3.0.0-alpha-1, 2.5.0
>
>
> When I was solving HBASE-25745
> ([PR3139|https://github.com/apache/hbase/pull/3139]), I found that our use of
> Configuration#addDeprecation API was wrong.
>
> At present, we will call Configuration#addDeprecation in the static block for
> the deprecated configuration. But after testing, it is found that this does
> not complete backward compatibility. When user upgrades HBase and does not
> change the deprecated configuration to the new configuration, he will find
> that the deprecated configuration does not effect, which may not be
> consistent with expectations. The specific test results can be seen in the PR
> above, and we can found the calling order of Configuration#addDeprecation is
> very important.
>
> Configuration#addDeprecation is a Hadoop API, looking through the Hadoop
> source code, we will find that before creating the Configuration object, the
> addDeprecatedKeys() method will be called first:
> [https://github.com/apache/hadoop/blob/b93e448f9aa66689f1ce5059f6cdce8add130457/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/HdfsConfiguration.java#L34]
> .
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