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Date: Wed, 27 Sep 2017 20:28:00 +0000 (UTC)
From: "Xiao Chen (JIRA)" <jira@apache.org>
To: common-issues@hadoop.apache.org
Message-ID: <JIRA.13102679.1505507836000.219292.1506544080372@Atlassian.JIRA>
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Subject: [jira] [Commented] (HADOOP-14872) CryptoInputStream should
 implement unbuffer
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archived-at: Wed, 27 Sep 2017 20:28:05 -0000


    [ https://issues.apache.org/jira/browse/HADOOP-14872?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16183202#comment-16183202 ] 

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

Thanks [~jzhuge] and [~stevel@apache.org]!

Looks good to me too. My belated review nits:
- Please improve javadoc of {{StreamCapabilities$StreamCapability#isEqual()}}. 'only in case' could be clearer. This is what the underlying {{equalsIgnoreCase}} javadoc says:
{quote}
Compares this {@code String} to another {@code String}, ignoring case
     * considerations.  Two strings are considered equal ignoring case if they
     * are of the same length and corresponding characters in the two strings
     * are equal ignoring case.
{quote}
- Name of above method - how about just {{equalsIgnoreCase}} too?
- Unnecessary line break at javadoc of {{DROPBEHIND}}.
- {{CanUnbuffer}} javadoc could use some improvement. 'Implement this interface to indicate that they can clear their buffers on request.'
- Please remember to remove the test line from {{TestUnbuffer}} when commit. :)

Thank you.

> 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
>
>
> 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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