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From C G <parallel...@yahoo.com>
Subject Re: 0.16.4 DataNode problem...
Date Wed, 28 May 2008 21:50:04 GMT
I've repeated the experiment under more controlled circumstances:  by creating a new file system
formatted by 0.16.4 and then populating it.  In this scenario we see the same problem:  during
the reduce phase the DataNode instances consume more and more memory until the system fails.
 Further, our server monitoring shows us that at the time of failure, each node in the system
has about 7,000 open socket connections.
   
  We're now upgrading to 0.17.0 to repeat the same experiment, but I am pessimistic about
getting any resolution.
   
  Does anybody have any insight into what might be going on?  It seems really strange to have
code that works in an old version but won't run in the more modern releases.
   
  Thanks, 
  C G

C G <parallelguy@yahoo.com> wrote:
  Hi All:

I'm seeing an inability to run one of our applications over a reasonably small dataset (~200G
input) while running 0.16.4. Previously we were on 0.15.0 and the same application ran fine
with the same dataset.

A lengthy description follows, including log file output, etc. The failure mode smells like
a bug in 0.16.4, but I'm not 100% positive about that.

My questions are:

1. Any known issues upgrading from 0.15.0 to 0.16.4? Our code runs just fine over small datasets,
but dies on these larger ones. We followed the upgrade instructions in the wiki, etc.

2. Would an upgrade to 0.17.0 help resolve these problems?

3. Would a re-format/re-load of HDFS help correct these issues? This is the thing I hope for
the least in that I have 3T of data on-board HDFS and it will take days to dump it all and
reload it.

4. Any other advice or help?

I've been looking at this for the past few days and have been unable to make progress of solving
it. I would hate to have to fall back to 0.15.0 (see above regarding 3T data reloads, not
to mention being stuck on an old release). Any help, thoughts, comments, etc., would be very
helpful. Thanks!

Description:
Following an upgrade from 0.15.0 to 0.16.4 (and after recompiling our apps, etc.), a job that
used to run correctly on our grid now fails. The failure occurs after the map phase is complete,
and about 2/3rds of the way through the reduce job. The error which gets kicked out from the
application perspective is:

08/05/27 11:30:08 INFO mapred.JobClient: map 100% reduce 89%
08/05/27 11:30:41 INFO mapred.JobClient: map 100% reduce 90%
08/05/27 11:32:45 INFO mapred.JobClient: map 100% reduce 86%
08/05/27 11:32:45 INFO mapred.JobClient: Task Id : task_200805271056_0001_r_000007_0, Status
: FAILED
java.io.IOException: Could not get block locations. Aborting...
at org.apache.hadoop.dfs.DFSClient$DFSOutputStream.processDatanode Error(DFSClient.java:1832)
at org.apache.hadoop.dfs.DFSClient$DFSOutputStream.access$1100(DFSClient.java:1487)
at org.apache.hadoop.dfs.DFSClient$DFSOutputStream$DataStreamer.run(DFSClient.java:1579)


I then discovered that 1 or more DataNode instances on the slave nodes are down (we run 1
DataNode instance per machine). The cause for at least some of the DataNode failures is a
JVM internal error that gets raised due to a complete out-of-memory scenario (on a 4G, 4-way
machine). 

Watching the DataNodes run, I can see them consuming more and more memory. For those failures
for which there is a JVM traceback, I see (in part):
#
# java.lang.OutOfMemoryError: requested 16 bytes for CHeapObj-new. Out of swap space?
#
# Internal Error (414C4C4F434154494F4E0E494E4C494E450E4850500017), pid=4246, tid=2283883408
#
# Java VM: Java HotSpot(TM) Server VM (1.6.0_02-b05 mixed mode)
# If you would like to submit a bug report, please visit:
# http://java.sun.com/webapps/bugreport/crash.jsp
#
--------------- T H R E A D ---------------
Current thread (0x8a942000): JavaThread "org.apache.hadoop.dfs.DataNode$DataXceiver@3f4f44"
daemon [_thread_in_Java, id=15064]
Stack: [0x881c4000,0x88215000), sp=0x882139e0, free space=318k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0x53b707]
V [libjvm.so+0x225fe1]
V [libjvm.so+0x16fdc5]
V [libjvm.so+0x22aef3]
Java frames: (J=compiled Java code, j=interpreted, Vv=VM code)
v blob 0xf4f235a7
J java.io.DataInputStream.readInt()I
j org.apache.hadoop.dfs.DataNode$BlockReceiver.receiveBlock(Ljava/io/DataOutputStream;Ljava/io/DataInputStream;Ljava/io/DataOutputStream;Ljava/lang/String;Lorg/a
pache/hadoop/dfs/DataNode$Throttler;I)V+126
j org.apache.hadoop.dfs.DataNode$DataXceiver.writeBlock(Ljava/io/DataInputStream;)V+746
j org.apache.hadoop.dfs.DataNode$DataXceiver.run()V+174
j java.lang.Thread.run()V+11
v ~StubRoutines::call_stub
--------------- P R O C E S S ---------------
Java Threads: ( => current thread )
0x0ae3f400 JavaThread "process reaper" daemon [_thread_blocked, id=26870]
0x852e6000 JavaThread "org.apache.hadoop.dfs.DataNode$DataXceiver@e5dce1" daemon [_thread_in_vm,
id=26869]
0x08a1cc00 JavaThread "PacketResponder 0 for Block blk_-6186975972786687394" daemon [_thread_blocked,
id=26769]
0x852e5000 JavaThread "org.apache.hadoop.dfs.DataNode$DataXceiver@c40bf8" daemon [_thread_in_native,
id=26768]
0x0956e000 JavaThread "PacketResponder 0 for Block blk_-2322514873363546651" daemon [_thread_blocked,
id=26767]
0x852e4400 JavaThread "org.apache.hadoop.dfs.DataNode$DataXceiver@1ca61f9" daemon [_thread_in_native,
id=26766]
0x09d3a400 JavaThread "PacketResponder 0 for Block blk_8926941945313450801" daemon [_thread_blocked,
id=26764]
0x852e3c00 JavaThread "org.apache.hadoop.dfs.DataNode$DataXceiver@1e186d9" daemon [_thread_in_native,
id=26763]
0x0953d000 JavaThread "PacketResponder 0 for Block blk_4785883052769066976" daemon [_thread_blocked,
id=26762]
0xb13a5c00 JavaThread "org.apache.hadoop.dfs.DataNode$DataXceiver@13d62aa" daemon [_thread_in_native,
id=26761]

The interesting part here is that if I count the number of JavaThreads running org.apache.hadoop.dfs.DataNode
I see 4,538 (!) in the traceback. The number of threads was surprising.

Other DataNodes just exit without panicking the JVM. In either failure mode, the last few
lines of the DataNode log file is apparently innocuous:

2008-05-27 11:31:47,663 INFO org.apache.hadoop.dfs.DataNode: Datanode 2 got response for connect
ack from downstream datanode with firstbadlink as
2008-05-27 11:31:47,663 INFO org.apache.hadoop.dfs.DataNode: Datanode 2 forwarding connect
ack to upstream firstbadlink is
2008-05-27 11:31:48,268 INFO org.apache.hadoop.dfs.DataNode: Receiving block blk_-2241766430103062484
src: /10.2.14.10:33626 dest: /10.2.14.10:50010
2008-05-27 11:31:48,740 INFO org.apache.hadoop.dfs.DataNode: Receiving block blk_313239508245918539
src: /10.2.14.24:37836 dest: /10.2.14.24:50010
2008-05-27 11:31:48,740 INFO org.apache.hadoop.dfs.DataNode: Datanode 0 forwarding connect
ack to upstream firstbadlink is
2008-05-27 11:31:49,044 INFO org.apache.hadoop.dfs.DataNode: Receiving block blk_1684581399908730353
src: /10.2.14.16:51605 dest: /10.2.14.16:50010
2008-05-27 11:31:49,044 INFO org.apache.hadoop.dfs.DataNode: Datanode 0 forwarding connect
ack to upstream firstbadlink is
2008-05-27 11:31:49,509 INFO org.apache.hadoop.dfs.DataNode: Receiving block blk_2493969670086107736
src: /10.2.14.18:47557 dest: /10.2.14.18:50010
2008-05-27 11:31:49,513 INFO org.apache.hadoop.dfs.DataNode: Datanode 1 got response for connect
ack from downstream datanode with firstbadlink as
2008-05-27 11:31:49,513 INFO org.apache.hadoop.dfs.DataNode: Datanode 1 forwarding connect
ack to upstream firstbadlink is

Finally, the task-level output (in userlogs) doesn't reveal much either:

2008-05-27 11:38:30,724 INFO org.apache.hadoop.mapred.ReduceTask: task_200805271056_0001_r_000007_1
Need 34 map output(s)
2008-05-27 11:38:30,753 INFO org.apache.hadoop.mapred.ReduceTask: task_200805271056_0001_r_000007_1
done copying task_200805271056_0001_m_001976_0 output from worker9.
2008-05-27 11:38:31,727 INFO org.apache.hadoop.mapred.ReduceTask: task_200805271056_0001_r_000007_1:
Got 0 new map-outputs & 0 obsolete map-outputs from tasktracker and 0 map-outputs from
previous failures
2008-05-27 11:38:31,727 INFO org.apache.hadoop.mapred.ReduceTask: task_200805271056_0001_r_000007_1
Got 33 known map output location(s); scheduling...
2008-05-27 11:38:31,727 INFO org.apache.hadoop.mapred.ReduceTask: task_200805271056_0001_r_000007_1
Scheduled 1 of 33 known outputs (0 slow hosts and 32 dup hosts)
2008-05-27 11:38:31,727 INFO org.apache.hadoop.mapred.ReduceTask: task_200805271056_0001_r_000007_1
Copying task_200805271056_0001_m_001248_0 output from worker8.
2008-05-27 11:38:31,727 INFO org.apache.hadoop.mapred.ReduceTask: task_200805271056_0001_r_000007_1
Need 33 map output(s)
2008-05-27 11:38:31,752 INFO org.apache.hadoop.mapred.ReduceTask: task_200805271056_0001_r_000007_1
done copying task_200805271056_0001_m_001248_0 output from worker8.





       
       
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