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https://issues.apache.org/jira/browse/HADOOP-14872?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16171547#comment-16171547
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Steve Loughran commented on HADOOP-14872:
-----------------------------------------
off the record, I'm not happy that the HDFS team chose to implement a method
without: specifying it or taking any attempts to think about other filesystems.
now its being used in Apps (HBase catches and complains), here Impala breaks.
I think we need a more fundamental change than doing it piecemeal, and making
it a no-op with the hasCapabilities option oin 2.9+ would do this. I'm sure the
HDFS team will express concern when you and I patch their classes, but that's
what happens when you break downstream code.
> CryptoInputStream should implement unbuffer
> -------------------------------------------
>
> Key: HADOOP-14872
> URL: https://issues.apache.org/jira/browse/HADOOP-14872
> Project: Hadoop Common
> Issue Type: Improvement
> Components: fs
> Affects Versions: 2.6.4
> Reporter: John Zhuge
> Assignee: John Zhuge
> Attachments: HADOOP-14872.001.patch, HADOOP-14872.002.patch,
> HADOOP-14872.003.patch
>
>
> Discovered in IMPALA-5909.
> Opening an encrypted HDFS file returns a chain of wrapped input streams:
> {noformat}
> HdfsDataInputStream
> CryptoInputStream
> DFSInputStream
> {noformat}
> If an application such as Impala or HBase calls HdfsDataInputStream#unbuffer,
> FSDataInputStream#unbuffer will be called:
> {code:java}
> try {
> ((CanUnbuffer)in).unbuffer();
> } catch (ClassCastException e) {
> throw new UnsupportedOperationException("this stream does not " +
> "support unbuffering.");
> }
> {code}
> If the {{in}} class does not implement CanUnbuffer, UOE will be thrown. If
> the application is not careful, tons of UOEs will show up in logs.
> In comparison, opening an non-encrypted HDFS file returns this chain:
> {noformat}
> HdfsDataInputStream
> DFSInputStream
> {noformat}
> DFSInputStream implements CanUnbuffer.
> It is good for CryptoInputStream to implement CanUnbuffer for 2 reasons:
> * Release buffer, cache, or any other resource when instructed
> * Able to call its wrapped DFSInputStream unbuffer
> * Avoid the UOE described above. Applications may not handle the UOE very
> well.
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