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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-2341) Datanode active connections never returns to 0
Date Thu, 13 Dec 2007 19:09:43 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2341?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12551580
] 

Doug Cutting commented on HADOOP-2341:
--------------------------------------

> pread I mentioned is FSInputStream.read(long, buf, offset, len).

Michael is calling MapFile#get().  That uses a buffered stream, since calls might sometimes
be random, and they might sometimes be sequential, when enumerating a range of values.

It would certainly be nice if we could support keeping lots of HDFS files open without paying
a large penalty on either the client or on the datanode.  Perhaps idle connections to datanodes
should time out.  I think the existing client code would re-establish connections if the datanode
were simply to close idle connections after a time.  Could that work?



> 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 (org.apache.hadoop.dfs.DataNode$DataXceiver@166068b6):
>   State: RUNNABLE
>   Blocked count: 0
>   Waited count: 0
>   Stack:
>     java.net.SocketOutputStream.socketWrite0(Native Method)
>     java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:92)
>     java.net.SocketOutputStream.write(SocketOutputStream.java:136)
>     java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:65)
>     java.io.BufferedOutputStream.write(BufferedOutputStream.java:109)
>     java.io.DataOutputStream.write(DataOutputStream.java:90)
>     org.apache.hadoop.dfs.DataNode$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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