[jira] [Updated] (HADOOP-14872) CryptoInputStream should implement unbuffer

["John Zhuge (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HADOOP-14872?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

John Zhuge updated HADOOP-14872:
--------------------------------
    Attachment: HADOOP-14872.013.patch

Thanks Xiao and Steve for the patience and great discussions.

Patch 013
* Incorporate Xiao and Steve's comments
* Add {{StreamCapabilitiesPolicy#unbuffer}} to implement the policy for unbuffer. Java 8 static method for interface CanUnbuffer could be a good choice but we can't use it due to backport concern.
* Use a table in FileSystem.md to list capabilities
* Plan to commit StreamCapabilities enhancements in HADOOP-15012 first, then check in CryptoInputStream changes here.

> 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
>            Priority: Major
>         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, HADOOP-14872.013.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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