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https://issues.apache.org/jira/browse/HDFS-14111?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16777375#comment-16777375
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Todd Lipcon commented on HDFS-14111:
------------------------------------
{quote}
jthr = newJavaStr(env, "in:readbytebuffer", &jCapabilityString);
jthr = invokeMethod(env, &jVal, INSTANCE, jFile, HADOOP_ISTRM,
"hasCapability", "(Ljava/lang/String;)Z", jCapabilityString);
{quote}
We probably need to check 'jthr' from the newJavaStr before moving along to
invokeMethod, even though it's highly unlikely to hit an issue. (it could OOM)
Otherwise I think this makes sense. [[email protected]] does the
StreamCapabiltiies change look good to you?
> hdfsOpenFile on HDFS causes unnecessary IO from file offset 0
> -------------------------------------------------------------
>
> Key: HDFS-14111
> URL: https://issues.apache.org/jira/browse/HDFS-14111
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: hdfs-client, libhdfs
> Affects Versions: 3.2.0
> Reporter: Todd Lipcon
> Assignee: Sahil Takiar
> Priority: Major
> Attachments: HDFS-14111.001.patch, HDFS-14111.002.patch
>
>
> hdfsOpenFile() calls readDirect() with a 0-length argument in order to check
> whether the underlying stream supports bytebuffer reads. With DFSInputStream,
> the read(0) isn't short circuited, and results in the DFSClient opening a
> block reader. In the case of a remote block, the block reader will actually
> issue a read of the whole block, causing the datanode to perform unnecessary
> IO and network transfers in order to fill up the client's TCP buffers. This
> causes performance degradation.
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