Jan Van Besien 2013-11-14, 08:50
Brock Noland 2013-11-14, 16:07
Jan Van Besien 2013-11-13, 09:32
Brock Noland 2013-11-13, 14:03
Jan Van Besien 2013-11-18, 10:28
Brock Noland 2013-12-17, 17:51
Jan Van Besien 2013-11-18, 13:21
-Re: file channel read performance impacted by write rate
Jan Van Besien 2013-11-25, 08:46
Is anybody still looking into this question?
Should I log it in jira such that somebody can look into it later?
On 11/18/2013 11:28 AM, Jan Van Besien wrote:
> Sorry it took me a while to answer this. I compiled a small test case
> using only off the shelve flume components that shows what is going on.
> The setup is a single agent with http source, null sink and file
> channel. I am using the default configuration as much as possible.
> The test goes as follows:
> - start the agent without sink
> - run a script that sends http requests in multiple threads to the http
> source (the script simply calls the url http://localhost:8080/?key=value
> over and over a gain, whereby value is a random string of 100 chars).
> - this script does about 100 requests per second on my machine. I leave
> it running for a while, such that the file channel contains about 20000
> - add the null sink to the configuration (around 11:14:33 in the log).
> - observe the logging of the null sink. You'll see in the log file that
> it takes more than 10 seconds per 1000 events (until about even 5000,
> around 11:15:33)
> - stop the http request generating script (i.e. no more writing in file
> - observer the logging of the null sink: events 5000 until 20000 are all
> processed within a few seconds.
> In the attachment:
> - flume log
> - thread dumps while the ingest was running and the null sink was enabled
> - config (agent1.conf)
> I also tried with more sinks (4), see agent2.conf. The results are the same.
> Thanks for looking into this,
> On 11/14/2013 05:08 PM, Brock Noland wrote:
>> On Thu, Nov 14, 2013 at 2:50 AM, Jan Van Besien <[EMAIL PROTECTED]
>> <mailto:[EMAIL PROTECTED]>> wrote:
>> 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
>> > disks for the file channel.
>> I am already using multiple disks for the channel (4).
>> Can you share your configuration?
>> 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.
>> I would be curious to know though if you doubled the sinks if that would
>> give more time to readers. Could you take three-four thread dumps of the
>> JVM while it's in this state and share them?
Shangan Chen 2013-12-17, 12:27
Brock Noland 2013-12-17, 12:54
Shangan Chen 2013-12-17, 15:32
Brock Noland 2013-12-17, 16:13
Hari Shreedharan 2013-12-17, 17:11