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From Juhani Connolly <juhani_conno...@cyberagent.co.jp>
Subject Re: ExecSource->MemoryChannel->AvroSink->AvroSource->FileChannel->HDFSSink throughput question
Date Fri, 01 Feb 2013 02:12:07 GMT
Hi Chris,

The most likely cause of that error is that the sinks are draining 
requests slower than your sources are feeding fresh data. Over time it 
will fill up the capacity of your memory channel, which will then start 
refusing additional put requests.

You can confirm this by connecting with jmx or ganglia.

If the write is extremely bursty, it's possible that it's just 
temporarily going over the sink consumption rate, and increasing the 
channel capacity could work. Otherwise, increasing the avro batch size, 
or adding additional avro sinks(more threads) may also help. I think 
that setting up ganglia monitoring and looking at the incoming and 
outgoing event counts and channel fill states helps a lot in diagnosing 
these bottlenecks, you should look into doing that.

On 02/01/2013 02:01 AM, Chris Neal wrote:
> Hi all.
> I need some thoughts on sizing/tuning of the above (common) route in 
> FlumeNG to maximize throughput.  Here is my setup:
> *Source JVM (ExecSource/MemoryChannel/AvroSink):*
> -Xmx4g
> -Xms4g
> -XX:MaxDirectMemorySize=256m
> Number of ExecSources in config:  124 (yes, it's a ton.  Can't do 
> anything about it :)  The write rate to the source files is fairly 
> fast and bursty.
> ExecSource.batchSize = 1000
> (so, when all 124 tail -F instances get 1000 events, they all dump to 
> the memory channel)
> MemoryChannel.capacity = 1000000
> MemoryChannel.transactionCapacity = 1000
> (somewhat unclear on what this is.  Docs say "The number of events 
> stored in the channel per transaction", but what is a "transaction" to 
> a MemoryChannel?)
> AvroSink.batchSize = 1000
> *Destination JVM (AvroSource/FileChannel/HDFSSink)*
> (Cluster of two JVMs on two servers, each configured the same as per 
> below)
> -Xms=2g
> -Xmx=2g
> -XX:MaxDirectMemorySize is not defined, so whatever the default is
> AvroSource.threads = 64
> FileChannel.transactionCapacity = 1000
> FileChannel.capacity = 32000000
> HDFSSink.batchSize = 1000
> HDFSSink.threadPoolSize = 64
> With this configuration, in about 5 minutes, I get the common Exception:
> "Space for commit to queue couldn't be acquired Sinks are likely not 
> keeping up with sources, or the buffer size is too tight"
> on the Source JVM.  It is no where near the 4g max, rather only at 
> about 2.5g.
> I'm wondering about the logic of having all the batch 
> sizes/transaction sizes 1000.  My thought was that would keep from 
> fragmenting the transfer of data, but maybe that's flawed?  Should the 
> sizes be different?
> Also curious about increasing the MaxDirectMemorySize to something 
> larger than 256MB?  I tried removing it altogether in my Source JVM 
> (which makes the size unbounded), but that didn't seem to make a 
> difference.
> I'm having some trouble figuring out where the backup is happening, 
> and how to open up the gates. :)
> Thanks in advance for any suggestions.
> Chris

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