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From Juhani Connolly <juhani_conno...@cyberagent.co.jp>
Subject Re: Restarts without data loss
Date Tue, 10 Jul 2012 02:14:47 GMT
On 07/10/2012 02:36 AM, Brock Noland wrote:
> If you ran the workload with file channel and then took 10 thread
> dumps I think we'd have enough to understand what is going on.
> Brock
I've taken some dumps and you can find them here: 

I also included a png from visualvm's thread visualization where you can 
confirm that the source is constantly busy(trying to get stuff into the 
file channel), while the 5 sinks are pretty idle. Let me know if there's 
anything else I can provide

> On Mon, Jul 9, 2012 at 11:49 AM, Juhani Connolly
> <juhani_connolly@cyberagent.co.jp> wrote:
>> It is currently pushing only 10 events per second or so(roughly 250 bytes
>> per event). This is with datadir/checkpoint on the same directory. Of course
>> the fact that there is a tail process running and that tomcat is also
>> writing out logs is without a doubt compounding the problem somewhat.
>> I haven't taken a serious look at thread dumps of the file channel since I
>> don't have a thorough understanding of it. However analysis has involved
>> trying varying numbers of sinks(no throughput difference) and replacing with
>> memory channel(which easily handles the 650 ish requests per second we have
>> per server for the particular api, no problems even with a single sink).
>> Since you say there's heavy fsyncing, and with 7200rpm disks, each seek will
>> have an average latency of 4.16ms, so for alternating seeks between the
>> checkpoint and the data dir, if each of those writes happens in order,
>> you're already limited to best case of barely more than 100 events per
>> second. Our experience so far has shown it to be significantly less.
>> I do believe that batching a bunch of puts or takes with a single commit
>> together as two seeks followed by writes(or one if we can only use a single
>> storage file) could give significant returns when paired with a batching
>> sink/source(which many already do... Requesting multiple items at a time).
>> If there is any specific data you would like I would be happy to try and
>> provide it.
>> On 07/09/2012 05:22 PM, Brock Noland wrote:
>> On Mon, Jul 9, 2012 at 8:51 AM, Juhani Connolly
>> <juhani_connolly@cyberagent.co.jp> wrote:
>>>   - Intended setup with flume was a file channel connected to an avro sink.
>>> With only a single disk available, it is extremely slow. JDBC channel is
>>> also extremely slow, and MemoryChannel will fill up and start refusing puts
>>> as soon as a network issue comes up.
>> Have you taken a few thread dumps or done other analysis? When you say
>> "extremely slow" what do you mean? Configured for no dataloss FileChannel is
>> going to be doing a lot of fsync'ing so I am not surprised it's slow. That
>> is a property of disks not FileChannel. I think we should use group commit
>> but that shouldn't make it 10x faster.
>> Brock

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