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Posted to hdfs-issues@hadoop.apache.org by "Sahil Takiar (JIRA)" <ji...@apache.org> on 2019/02/21 16:30:00 UTC
[jira] [Updated] (HDFS-14111) hdfsOpenFile on HDFS causes
unnecessary IO from file offset 0
[ https://issues.apache.org/jira/browse/HDFS-14111?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Sahil Takiar updated HDFS-14111:
--------------------------------
Status: Patch Available (was: Open)
> 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
>
>
> 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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