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From "Mangtani, Kushal" <Kushal.Mangt...@viasat.com>
Subject RE: File Channel Exception "Failed to obtain lock for writing to the log.Try increasing the log write timeout value"
Date Thu, 27 Feb 2014 18:48:34 GMT
Hari,

Thanks for the prompt reply. The current file channel’s  write-timeout = 30 sec .EBS drive
current  capacity = 200 GB . The rate of writes is 60 events/min; where each event is approx.
40 KB.

I am thinking of increase file channel write-timeout to 60 sec. What do you suggest?
Also,one strange thing I noticed all the flume-collectors  also get the same exception.However,
all have a separate ebs drive. Any inputs?

Thanks,
Kushal Mangtani

From: Hari Shreedharan [mailto:hshreedharan@cloudera.com]
Sent: Thursday, February 27, 2014 10:35 AM
To: user@flume.apache.org
Subject: Re: File Channel Exception "Failed to obtain lock for writing to the log.Try increasing
the log write timeout value"

For now, increase the file channel’s write-timeout parameter to around 30 or so (basically
file channel is timing out while writing to disk). But the basic problem you are seeing is
that your EBS instance is very slow and IO is taking too long. You either need to increase
your EBS IO capacity, or reduce the rate or writes.


Thanks,
Hari


On Thursday, February 27, 2014 at 10:28 AM, Mangtani, Kushal wrote:





From: Mangtani, Kushal
Sent: Wednesday, February 26, 2014 4:51 PM
To: 'user@flume.apache.org<mailto:user@flume.apache.org>'; 'user-subscribe@flume.apache.org<mailto:user-subscribe@flume.apache.org>'
Cc: Rangnekar, Rohit; 'dev@flume.apache.org<mailto:dev@flume.apache.org>'
Subject: File Channel Exception "Failed to obtain lock for writing to the log.Try increasing
the log write timeout value"



Hi,



I'm using Flume-Ng 1.4 cdh4.4 Tarball for collecting aggregated logs.

I am running a 2 tier(agent,collector) Flume Configuration with custom plugins. There are
approximately 20 agents (receiving data) and 6 collector flume (writing to HDFS) machines
all running independenly. However, I have been facing some File Channel Exceptions on the
collector side. The agent appears to be working fine.



 Error  stacktrace:

                             org.apache.flume.ChannelException: Failed to obtain lock for
writing to the log. Try increasing the log write timeout value. [channel=c2]

                             at org.apache.flume.channel.file.FileChannel$FileBackedTransaction.doRollback(FileChannel.java:621)

                             at org.apache.flume.channel.BasicTransactionSemantics.rollback(BasicTransactionSemantics.java:168)

                             at org.apache.flume.sink.hdfs.HDFSEventSink.process(HDFSEventSink.java:421)

                             at org.apache.flume.sink.DefaultSinkProcessor.process(DefaultSinkProcessor.java:68)

                             at org.apache.flume.SinkRunner$PollingRunner.run(SinkRunner.java:147)

                             …..

                             And I keep on getting the same error



                             P.S :This same exception is repated in most of the flume collector
machines.But, not at the same duration. There is usually a difference of a couple of hours
or more.



1.  HDFS sinks are written in  the Amazon EC2 cloud instance.

2. datadir and checkpoint dir of file channel in all flume collector instances are mounted
to a separate hadoop ebs drive .This makes sure that two separate collectors do not overlap
their log and checkpoint dir. There is a symbolic link i.e /usr/lib/flume-ng/datasource -->
/hadoop/ebs/mnt-1

3. The Flume works fine for a couple of days and all the agent,collector are initialized properly
without exceptions.



Questions:

Exception “Failed to obtain lock for writing to the log. Try increasing the log write timeout
value . [channel=c2]” . According to the documentation, such an exception occurs only if
two processes are acceesing the same file/directory. However, each channel is configured separately
so No two channels should access the same dir. Hence, this exception does not indicates anything.
Please correct me, if im wrong.

Also, HDFS.CallTimeout – indicates calling HDFS for open,write operations. If no response
within a duration, it timeouts. And , if its timeouts; it closes the File. Please correct
me, if im wrong.  Also, if there is a way to specify the number of retries before it closes
the file?



Your inputs/suggestions will be thoroughly appreciated.





Regards

Kushal Mangtani

Software Engineer



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