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From "John Zhuge (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-14872) CryptoInputStream should implement unbuffer
Date Thu, 28 Sep 2017 21:18:07 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-14872?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16184893#comment-16184893
] 

John Zhuge commented on HADOOP-14872:
-------------------------------------

What if hasCapability is called with the name of the enum, not the value, e.g. {{in.hasCapability(StreamCapability.UNBUFFER.name()}?
If so, field {{StreamCapability#capability}} is not needed.
{code:java}
  public boolean hasCapability(String capability) {
    try {
      switch (StreamCapability.valueOf(capability)) {
      case READAHEAD:
      case DROPBEHIND:
      case UNBUFFER:
        return true;
      }
      return false;
    } catch (IllegalArgumentException iae) {
      return false;
    }
  }
{code}

Or change hasCapability parameter type from String to Enum, but I understand we'd like to
support any string, not the enums in StreamCapability, right?

> 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
>
>
> 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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