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https://issues.apache.org/jira/browse/HADOOP-2341?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12551222
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Raghu Angadi commented on HADOOP-2341:
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Sure. Please keep the Jira open if you think there is a bug.
pread I mentioned is FSInputStrea.read(long, buf, offset, len).
> Is there an issue to move the datanode to use select that you know of?
What does that fix? What is the problem it is causing now? It surely won't fix
900 (unaccounted) connections. IMHO reducing threads on Datanode just fixes
just one of the symptoms and does not address the real issue of using streaming
api to do sparse random reads.
> Datanode active connections never returns to 0
> ----------------------------------------------
>
> Key: HADOOP-2341
> URL: https://issues.apache.org/jira/browse/HADOOP-2341
> Project: Hadoop
> Issue Type: Bug
> Components: dfs
> Affects Versions: 0.16.0
> Reporter: Paul Saab
> Attachments: dfsclient.patch, hregionserver-stack.txt,
> stacks-XX.XX.XX.XXX.txt, stacks-YY.YY.YY.YY.txt
>
>
> On trunk i continue to see the following in my data node logs:
> 2007-12-03 15:46:47,696 DEBUG dfs.DataNode - XX.XX.XX.XXX:50010:Number of
> active connections is: 42
> 2007-12-03 15:46:48,135 DEBUG dfs.DataNode - XX.XX.XX.XXX:50010:Number of
> active connections is: 41
> 2007-12-03 15:46:48,439 DEBUG dfs.DataNode - XX.XX.XX.XXX:50010:Number of
> active connections is: 40
> 2007-12-03 15:46:48,479 DEBUG dfs.DataNode - XX.XX.XX.XXX:50010:Number of
> active connections is: 39
> 2007-12-03 15:46:48,611 DEBUG dfs.DataNode - XX.XX.XX.XXX:50010:Number of
> active connections is: 38
> 2007-12-03 15:46:48,898 DEBUG dfs.DataNode - XX.XX.XX.XXX:50010:Number of
> active connections is: 37
> 2007-12-03 15:46:48,989 DEBUG dfs.DataNode - XX.XX.XX.XXX:50010:Number of
> active connections is: 36
> 2007-12-03 15:46:51,010 DEBUG dfs.DataNode - XX.XX.XX.XXX:50010:Number of
> active connections is: 35
> 2007-12-03 15:46:51,758 DEBUG dfs.DataNode - XX.XX.XX.XXX:50010:Number of
> active connections is: 34
> 2007-12-03 15:46:52,148 DEBUG dfs.DataNode - XX.XX.XX.XXX:50010:Number of
> active connections is: 33
> This number never returns to 0, even after many hours of no new data being
> manipulated or added into the DFS.
> Looking at netstat -tn i see significant amount of data in the send-q that
> never goes away:
> tcp 0 34240 ::ffff:XX.XX.XX.XXX:50010 ::ffff:YY.YY.YY.YY:55792
> ESTABLISHED
> tcp 0 38968 ::ffff:XX.XX.XX.XXX:50010 ::ffff:YY.YY.YY.YY:38169
> ESTABLISHED
> tcp 0 38456 ::ffff:XX.XX.XX.XXX:50010 ::ffff:YY.YY.YY.YY:35456
> ESTABLISHED
> tcp 0 29640 ::ffff:XX.XX.XX.XXX:50010 ::ffff:YY.YY.YY.YY:59845
> ESTABLISHED
> tcp 0 50168 ::ffff:XX.XX.XX.XXX:50010 ::ffff:YY.YY.YY.YY:44584
> ESTABLISHED
> When sniffing the network I see that the remote side (YY.YY.YY.YY) is
> returning a window size of 0
> 16:11:41.760474 IP XX.XX.XX.XXX.50010 > YY.YY.YY.YY.44584: . ack 3339984123
> win 46 <nop,nop,timestamp 1786247180 885681789>
> 16:11:41.761597 IP YY.YY.YY.YY.44584 > XX.XX.XX.XXX.50010: . ack 1 win 0
> <nop,nop,timestamp 885801786 1775711351>
> Then we look at the stack traces on each datanode, I will have tons of
> threads that *never* go away in the following trace:
> {code}
> Thread 6516 ([EMAIL PROTECTED]):
> State: RUNNABLE
> Blocked count: 0
> Waited count: 0
> Stack:
> java.net.SocketOutputStream.socketWrite0(Native Method)
> java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:92)
> java.net.SocketOutputStream.write(SocketOutputStream.java:136)
> java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:65)
> java.io.BufferedOutputStream.write(BufferedOutputStream.java:109)
> java.io.DataOutputStream.write(DataOutputStream.java:90)
> org.apache.hadoop.dfs.DataNode$BlockSender.sendChunk(DataNode.java:1400)
> org.apache.hadoop.dfs.DataNode$BlockSender.sendBlock(DataNode.java:1433)
> org.apache.hadoop.dfs.DataNode$DataXceiver.readBlock(DataNode.java:904)
> org.apache.hadoop.dfs.DataNode$DataXceiver.run(DataNode.java:849)
> java.lang.Thread.run(Thread.java:619)
> {code}
> Unfortunately there's very little in the logs with exceptions that could
> point to this. I have some exceptions the following, but nothing that points
> to problems between XX and YY:
> {code}
> 2007-12-02 11:19:47,889 WARN dfs.DataNode - Unexpected error trying to
> delete block blk_4515246476002110310. Block not found in blockMap.
> 2007-12-02 11:19:47,922 WARN dfs.DataNode - java.io.IOException: Error in
> deleting blocks.
> at org.apache.hadoop.dfs.FSDataset.invalidate(FSDataset.java:750)
> at org.apache.hadoop.dfs.DataNode.processCommand(DataNode.java:675)
> at org.apache.hadoop.dfs.DataNode.offerService(DataNode.java:569)
> at org.apache.hadoop.dfs.DataNode.run(DataNode.java:1720)
> at java.lang.Thread.run(Thread.java:619)
> {code}
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