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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-210) Namenode not able to accept connections
Date Tue, 23 May 2006 17:19:30 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-210?page=comments#action_12412958 ] 

Doug Cutting commented on HADOOP-210:
-------------------------------------

Threads are already pooled, with a single thread per client JVM.

The solution is either to not cache connections, using a new connection per request, or to
use selectors, so that a single thread can efficiently handle requests on all connections.
 In the latter case, we need to alter the request protocol so that incoming requests can be
buffered until they are complete, and then dispatched to a worker thread.  Currently a request
cannot be parsed except by a readFields method, so there's no way for generic server code
to tell when one request ends and the next begins.  So we can simply first write requests
to a buffer on the client, then send them length-prefixed.

> Namenode not able to accept connections
> ---------------------------------------
>
>          Key: HADOOP-210
>          URL: http://issues.apache.org/jira/browse/HADOOP-210
>      Project: Hadoop
>         Type: Bug

>   Components: dfs
>  Environment: linux
>     Reporter: Mahadev konar
>     Assignee: Mahadev konar

>
> I am running owen's random writer on a 627 node cluster (writing 10GB/node).  After running
for a while (map 12% reduce 1%) I get the following error on the Namenode:
> Exception in thread "Server listener on port 60000" java.lang.OutOfMemoryError: unable
to create new native thread
>         at java.lang.Thread.start0(Native Method)
>         at java.lang.Thread.start(Thread.java:574)
>         at org.apache.hadoop.ipc.Server$Listener.run(Server.java:105)
> After this, the namenode does not seem to be accepting connections from any of the clients.
All the DFSClient calls get timeout. Here is a trace for one of them:
> java.net.SocketTimeoutException: timed out waiting for rpc response
> 	at org.apache.hadoop.ipc.Client.call(Client.java:305)
> 	at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:149)
> 	at org.apache.hadoop.dfs.$Proxy1.open(Unknown Source)
> 	at org.apache.hadoop.dfs.DFSClient$DFSInputStream.openInfo(DFSClient.java:419)
> 	at org.apache.hadoop.dfs.DFSClient$DFSInputStream.(DFSClient.java:406)
> 	at org.apache.hadoop.dfs.DFSClient.open(DFSClient.java:171)
> 	at org.apache.hadoop.dfs.DistributedFileSystem.openRaw(DistributedFileSystem.java:78)
> 	at org.apache.hadoop.fs.FSDataInputStream$Checker.(FSDataInputStream.java:46)
> 	at org.apache.hadoop.fs.FSDataInputStream.(FSDataInputStream.java:228)
> 	at org.apache.hadoop.fs.FileSystem.open(FileSystem.java:157)
> 	at org.apache.hadoop.mapred.TextInputFormat.getRecordReader(TextInputFormat.java:43)
> 	at org.apache.hadoop.mapred.MapTask.run(MapTask.java:105)
> 	at org.apache.hadoop.mapred.TaskTracker$Child.main(TaskTracker.java:785).
> The namenode then has around 1% CPU utilization at this time (after the outofmemory exception
has been thrown). I have profiled the NameNode and it seems to be using around a maixmum heap
size of 57MB (which is not much). So, heap size does not seem to be a problem. It might be
happening due to lack of Stack space? Any pointers?

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