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From Jan Van Besien <ja...@ngdata.com>
Subject Re: file channel read performance impacted by write rate
Date Thu, 14 Nov 2013 08:50:55 GMT
On 11/13/2013 03:04 PM, Brock Noland wrote:
> The file channel uses a WAL which sits on disk.  Each time an event is
> committed an fsync is called to ensure that data is durable. Without
> this fsync there is no durability guarantee. More details here:
> https://blogs.apache.org/flume/entry/apache_flume_filechannel

Yes indeed. I was just not expecting the performance impact to be that big.

> The issue is that when the source is committing one-by-one it's
> consuming the disk doing an fsync for each event.  I would find a way to
> batch up the requests so they are not written one-by-one or use multiple
> disks for the file channel.

I am already using multiple disks for the channel (4). Batching the 
requests is indeed what I am doing to prevent the filechannel to be the 
bottleneck (using a flume agent with a memory channel in front of the 
agent with the file channel), but it inheritely means that I loose 
end-to-end durability because events are buffered in memory before being 
flushed to disk.

thanks,
Jan


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