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From "Hegner, Travis" <THeg...@trilliumit.com>
Subject RE: High ingest rate and FIN_WAIT1 problems
Date Fri, 16 Jul 2010 16:07:25 GMT
Hi Thomas,

I ran into a very similar issue when running slony-I on postgresql to replicate 15-20 databases.

Adjusting the TCP_FIN_TIMEOUT parameters for the kernel may help to slow (or hopefully stop),
the leaking sockets. I found some notes about adjusting TCP parameters here: http://www.hikaro.com/linux/tweaking-tcpip-syctl-conf.html

with the specific excerpt regarding the TCP_FIN_TIMEOUT:

TCP_FIN_TIMEOUT
This setting determines the time that must elapse before TCP/IP can release a closed connection
and reuse its resources. During this TIME_WAIT state, reopening the connection to the client
costs less than establishing a new connection. By reducing the value of this entry, TCP/IP
can release closed connections faster, making more resources available for new connections.
Addjust this in the presense of many connections sitting in the TIME_WAIT state:


# echo 30 > /proc/sys/net/ipv4/tcp_fin_timeout

Try setting this lower on your master. You may also consider these on the same link:

TCP_TW_RECYCLE
It enables fast recycling of TIME_WAIT sockets. The default value is 0 (disabled). The sysctl
documentation incorrectly states the default as enabled. It can be changed to 1 (enabled)
in many cases. Known to cause some issues with hoststated (load balancing and fail over) if
enabled, should be used with caution.


echo 1 > /proc/sys/net/ipv4/tcp_tw_recycle

TCP_TW_REUSE
This allows reusing sockets in TIME_WAIT state for new connections when it is safe from protocol
viewpoint. Default value is 0 (disabled). It is generally a safer alternative to tcp_tw_recycle


echo 1 > /proc/sys/net/ipv4/tcp_tw_reuse


The above commands will not persist reboots, but the link explains how. The list experts may
be able to give more insight on which, if any, of these settings are safe to manipulate, and
what risks or issues you may encounter specifically with Hbase while adjusting these settings.

Hope This Helps,

Travis Hegner


-----Original Message-----
From: Thomas Downing [mailto:tdowning@proteus-technologies.com]
Sent: Friday, July 16, 2010 10:33 AM
To: user@hbase.apache.org
Subject: High ingest rate and FIN_WAIT1 problems

Hi,

I am a complete HBase and HDFS newbie, so I apologize in advance for
the inevitable bloopers.

We are doing feasibility testing on NoSql data store options, with rather
high ingest rate requirements.  So far, HBase is looking good, with only
one issue identified. Running at an ingest rate of ~30K rows per second
on a 4 2.2Mhz CPU 8G RAM machine I am slowly leaking sockets.

This is a single node setup - no replication.  The CPU load is only about
50%-60%, with the majority of that in userland, system and iowait are
averaging less than 3%.  There is no swapping going on.

The problem is that on the datanode there are a large number of sockets
in FIN_WAIT1, with corresponding peers on master in ESTABLISHED.
These pairs hang around for quite some time, at at my ingest rate this
means that the total sockets held by datanode and master is slowly going
up.

If my understanding of TCP is correct, then this indicates that the master
peer has stopped reading incoming data from the datanode - i.e, it is
sending a window of zero; and that the datanode has called close(2) on
it's peer.

There was a thread some time ago:

http://www.mail-archive.com/hbase-user@hadoop.apache.org/msg03329.html

There was no real conclusion.  I have played with the config params as
suggested on that thread, but no luck yet.  Also, in that case the problem
seemed to be between datanodes for replication operations - not the case
with me.  Changing timeouts to avoid the slow increase might not really
solve the problem IFF the master peer has in fact ceased to read it's
socket.  The data outstanding in the TCP stack buffer would be lost.
Whether that would imply data loss is beyond me.

I am posting this here as although the only logs with errors/exceptions
are the datanode logs, netstat and wireshark seem to indicate that the
problem is on the master side.

The master, namenode, regionserver and zookeeper and logs shows no
warning or errors.  The datanode log shows this, over and over:

2010-07-16 00:33:09,269 WARN
org.apache.hadoop.hdfs.server.datanode.DataNode:
DatanodeRegistration(127.0.0.1:50010,
storageID=DS-1028643313-10.1.1.200-50010-1279026099917, infoPort=50075,
ipcPort=50020):Got exception while serving blk_3684861726145519813_22386
to /127.0.0.1:
java.net.SocketTimeoutException: 480000 millis timeout while waiting for
channel to be ready for write. ch :
java.nio.channels.SocketChannel[connected local=/127.0.0.1:50010
remote=/127.0.0.1:54774]
         at
org.apache.hadoop.net.SocketIOWithTimeout.waitForIO(SocketIOWithTimeout.java:246)
         at
org.apache.hadoop.net.SocketOutputStream.waitForWritable(SocketOutputStream.java:159)
         at
org.apache.hadoop.net.SocketOutputStream.transferToFully(SocketOutputStream.java:198)
         at
org.apache.hadoop.hdfs.server.datanode.BlockSender.sendChunks(BlockSender.java:313)
         at
org.apache.hadoop.hdfs.server.datanode.BlockSender.sendBlock(BlockSender.java:400)
         at
org.apache.hadoop.hdfs.server.datanode.DataXceiver.readBlock(DataXceiver.java:180)
         at
org.apache.hadoop.hdfs.server.datanode.DataXceiver.run(DataXceiver.java:95)
         at java.lang.Thread.run(Thread.java:619)

2010-07-16 00:33:09,269 ERROR
org.apache.hadoop.hdfs.server.datanode.DataNode:
DatanodeRegistration(127.0.0.1:50010,
storageID=DS-1028643313-10.1.1.200-50010-1279026099917, infoPort=50075,
ipcPort=50020):DataXceiver
java.net.SocketTimeoutException: 480000 millis timeout while waiting for
channel to be ready for write. ch :
java.nio.channels.SocketChannel[connected local=/127.0.0.1:50010
remote=/127.0.0.1:54774]
         at
org.apache.hadoop.net.SocketIOWithTimeout.waitForIO(SocketIOWithTimeout.java:246)
         at
org.apache.hadoop.net.SocketOutputStream.waitForWritable(SocketOutputStream.java:159)
         at
org.apache.hadoop.net.SocketOutputStream.transferToFully(SocketOutputStream.java:198)
         at
org.apache.hadoop.hdfs.server.datanode.BlockSender.sendChunks(BlockSender.java:313)
         at
org.apache.hadoop.hdfs.server.datanode.BlockSender.sendBlock(BlockSender.java:400)
         at
org.apache.hadoop.hdfs.server.datanode.DataXceiver.readBlock(DataXceiver.java:180)
         at
org.apache.hadoop.hdfs.server.datanode.DataXceiver.run(DataXceiver.java:95)
         at java.lang.Thread.run(Thread.java:619)

It there is any other info that might help, or any steps you would like
me to take, just let me know.

Thanks

Thomas Downing

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