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https://issues.apache.org/jira/browse/HDFS-15567?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17210550#comment-17210550
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Konstantin Shvachko commented on HDFS-15567:
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Thanks for taking a look [~vagarychen].
* Both {{FileSystem}} and {{AbstractFileSystem}} throw
{{UnsupportedOperationException}} with my patch. This is a standard pattern and
a way for clients to learn if the operation is supported or not in the
implementation. No-op will hide the problem and for {{mscyn}} in particular can
lead to inconsistent results further down the road, which is hard to debug as
we both know.
* Logging in the tests is not "required", but it helped a lot in debugging
problems that I fixed when some tests were failing. I decided to leave them in
the code in case something breaks in the future. I agree we usually try to
restrict change to bare minimum to avoid conflicts while backporting. In this
case with code relatively recent I don't see it a blocker for backports.
* Ran tests that failed on Jenkins locally. All passed. They are long running
tests, which frequently fail on Jenkins builds.
> [SBN Read] HDFS should expose msync() API to allow downstream applications
> call it explicetly.
> ----------------------------------------------------------------------------------------------
>
> Key: HDFS-15567
> URL: https://issues.apache.org/jira/browse/HDFS-15567
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: ha, hdfs-client
> Affects Versions: 2.10.0
> Reporter: Konstantin Shvachko
> Assignee: Konstantin Shvachko
> Priority: Major
> Attachments: HDFS-15567.001.patch, HDFS-15567.002.patch
>
>
> Consistent reads from Standby introduced {{msync()}} API HDFS-13688, which
> updates client's state ID with current state of the Active NameNode to
> guarantee consistency of subsequent calls to an ObserverNode. Currently this
> API is exposed via {{DFSClient}} only, which makes it hard for applications
> to access {{msync()}}. One way is to use something like this:
> {code}
> if(fs instanceof DistributedFileSystem) {
> ((DistributedFileSystem)fs).getClient().msync();
> }
> {code}
> This should be exposed both for {{FileSystem}} and {{FileContext}}.
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