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From "Xiao Chen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-14872) CryptoInputStream should implement unbuffer
Date Thu, 19 Oct 2017 16:52:00 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-14872?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16211349#comment-16211349
] 

Xiao Chen commented on HADOOP-14872:
------------------------------------

I'm okay to not add the 1-sentence explanations here.

Patch is not so big, perhaps cleaner if we do the API level change in 1 jira, and 'crypto
input stream implement unbuffer' in another. The second will still depend on the first, so
doesn't save any backport efforts etc. I'm really fine either way.

bq. Do you strongly prefer "clear" to "clean"?
clear v.s. clean not strong, though internally it's calling 'clear'. Descriptor v.s. Decryptor
is strong, since it looks to be a typo.

> 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,
HADOOP-14872.004.patch, HADOOP-14872.005.patch, HADOOP-14872.006.patch, HADOOP-14872.007.patch,
HADOOP-14872.008.patch, HADOOP-14872.009.patch, HADOOP-14872.010.patch, HADOOP-14872.011.patch,
HADOOP-14872.012.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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