[jira] [Assigned] (HDFS-8797) WebHdfsFileSystem creates too many connections for pread

["Jing Zhao (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDFS-8797?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jing Zhao reassigned HDFS-8797:
-------------------------------

    Assignee: Jing Zhao

> WebHdfsFileSystem creates too many connections for pread
> --------------------------------------------------------
>
>                 Key: HDFS-8797
>                 URL: https://issues.apache.org/jira/browse/HDFS-8797
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: webhdfs
>            Reporter: Jing Zhao
>            Assignee: Jing Zhao
>
> While running a test we found that WebHdfsFileSystem can create several thousand connections when doing a position read of a 200MB file. For each connection the client will connect to the DataNode again and the DataNode will create a new DFSClient instance to handle the read request. This also leads to several thousand {{getBlockLocations}} call to the NameNode.
> The cause of the issue is that in {{FSInputStream#read(long, byte[], int, int)}}, each time the inputstream reads some time, it seeks back to the old position and resets its state to SEEK. Thus the next read will regenerate the connection.
> {code}
>   public int read(long position, byte[] buffer, int offset, int length)
>     throws IOException {
>     synchronized (this) {
>       long oldPos = getPos();
>       int nread = -1;
>       try {
>         seek(position);
>         nread = read(buffer, offset, length);
>       } finally {
>         seek(oldPos);
>       }
>       return nread;
>     }
>   }
> {code}



--
This message was sent by Atlassian JIRA
(v6.3.4#6332)