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https://issues.apache.org/jira/browse/HDFS-14111?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16775747#comment-16775747
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Wei-Chiu Chuang commented on HDFS-14111:
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I think using the StreamCapabilities is the perfect solution.
I am less familiar with libhdfs, so [~stakiar] could you double check to make
sure the failed CTEST is unrelated?
{quote}
[ RUN ] HdfsExtTest.TestReadStats
Formatting using clusterid: testClusterID
/testptch/hadoop/hadoop-hdfs-project/hadoop-hdfs-native-client/src/main/native/libhdfspp/tests/hdfs_ext_test.cc:506:
Failure
Value of: (*__errno_location ())
Actual: 2
Expected: 0
[ FAILED ] HdfsExtTest.TestReadStats (1655 ms)
{quote}
> 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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