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https://issues.apache.org/jira/browse/HDFS-14789?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Haibin Huang updated HDFS-14789:
--------------------------------
Summary: namenode should avoid slow node when choose target in
BlockPlacementPolicyDefault (was: namenode should check slow node when
assigning a node for writing block )
> namenode should avoid slow node when choose target in
> BlockPlacementPolicyDefault
> ---------------------------------------------------------------------------------
>
> Key: HDFS-14789
> URL: https://issues.apache.org/jira/browse/HDFS-14789
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Haibin Huang
> Assignee: Haibin Huang
> Priority: Major
> Attachments: HDFS-14789
>
>
> With HDFS-11194 and HDFS-11551, we can find slow node through namenode's jmx.
> So i think namenode should check these slow nodes when assigning a node for
> writing block. If namenode choose a node at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault#*chooseRandom()*,
> we should check whether it's belong to slow node, because choosing a slow
> one to write data may take a long time, which can cause a client writing
> data very slowly and even encounter a socket timeout exception like this:
>
> {code:java}
> 2019-08-19,17:16:41,181 WARN org.apache.hadoop.hdfs.DFSClient: DataStreamer
> Exceptionjava.net.SocketTimeoutException: 495000 millis timeout while waiting
> for channel to be ready for write. ch :
> java.nio.channels.SocketChannel[connected local=/xxx:xxx remote=/xxx:xxx] at
> org.apache.hadoop.net.SocketIOWithTimeout.doIO(SocketIOWithTimeout.java:164)
> at
> org.apache.hadoop.net.SocketOutputStream.write(SocketOutputStream.java:159)
> at
> org.apache.hadoop.net.SocketOutputStream.write(SocketOutputStream.java:117)
> at java.io.BufferedOutputStream.write(BufferedOutputStream.java:122) at
> java.io.DataOutputStream.write(DataOutputStream.java:107) at
> org.apache.hadoop.hdfs.DFSOutputStream$Packet.writeTo(DFSOutputStream.java:328)
> at
> org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.run(DFSOutputStream.java:653){code}
>
> I use *maxChosenCount* to prevent choosing datanode task too long, which is
> calculated by the logarithm of probability, and it also can guarantee the
> probability of choosing a slow node to write block less than 0.01%.
> Finally, i use an expire time to let namnode don't choose these slow nodes
> within a specify period, because these slow nodes may have returned to normal
> after the period and can use to write block again.
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