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From Michal Taborsky <michal.tabor...@nrholding.com>
Subject Re: Logs used as Flume Sources and real-time analytics
Date Tue, 07 Feb 2012 12:16:22 GMT
Hi Alex,

truth be told, I am quite satisfied with the file tailing and I'll try to
explain why I like it. The main reason is, at least for us, the web
application itself is business critical, the event collection is not.
Writing to a plain file is a thing that can rarely fail and if it fails, it
fails quickly and in a controlled fashion. But piping to a flume agent for
example? How sure can I be, that the write will work all the time or fail
immediately? That it will not wait for some timeout or the other? Or throw
some unexpected error and bring down the app.

The other aspect is simple development and debugging. Any developer can
read a plain file and check if the data he's writing is correct, but with
any sophisticated method you either need more complicated testing
environment or redirection switches that will write to files in development
and to flume in testing and production, which complicates stuff.

Michal Táborský*
*chief systems architect*
Netretail Holding, BV
nrholding.com <http://www.nrholding.com>

2012/2/7 alo alt <wget.null@googlemail.com>

> Hi,
> sorry for pitching in, but FlumeNG will not support tailing sources,
> because we have here a lot of problems. First, and mostly the worst problem
> is the marker in a tailing file. If the agent crash, or the server, or the
> collector the marker will be lost. So, if you restart you'll getting all
> events again. Sure, you can use append, but here you get lost events.
> For a easy migration from flume to flumeNG use sources which are supported
> in NG. Syslog as example, more sources you can found here:
> https://cwiki.apache.org/FLUME/flume-ng.html
> You could use Avro for the sessions, and you could pipe direct to a local
> flume agent. Also syslog with a buffering mode could be work. Also in
> flumeNG now we have hBase handler and thrift.
> Another idea for collecting sessions could be
> http://hadoop.apache.org/common/docs/r1.0.0/webhdfs.html , an REST api
> for hdfs?
> - Alex
> --
> Alexander Lorenz
> http://mapredit.blogspot.com
> On Feb 7, 2012, at 11:14 AM, Alain RODRIGUEZ wrote:
> > Thank you for your answer it helps me a lot knowing I'am doing things in
> a good way.
> >
> > I've got an other question: How do you manage restart the service after
> a crash ? I mean, you tail the log file, so if your server crashes or you
> stop the tail for any reason, how do you do not to tail all the logs from
> the start, how do you manage restarting from the exact point where you left
> your tail process ?
> >
> > Thanks again for your help, I really appreciate :-).
> >
> > Alain
> >
> > 2012/2/2 Michal Taborsky <michal.taborsky@nrholding.com>
> > Hello Alain,
> >
> > we are using Flume for probably the same purposes. We are writing JSON
> encoded event data to flat file on every application server. Since each
> application server writes only maybe tens of events per second, the
> performance hit of writing to disk is negligible (and the events are
> written to disk only after the content is generated and sent to the user,
> so there is no latency for the end user). This file is tailed by Flume and
> delivered thru collectors to HDFS. The collectors are forking the events to
> RabbitMQ as well. We have a Node.js application, that picks up these events
> and does some real-time analytics on them. The delay between event
> origination and analytics is below 10 seconds, usually 1-3 seconds in total.
> >
> > Hope this helps.
> >
> > --
> > Michal Táborský
> > chief systems architect
> > Netretail Holding, BV
> > nrholding.com
> >
> >
> >
> >
> > 2012/2/2 Alain RODRIGUEZ <arodrime@gmail.com>
> > Hi,
> >
> > I'm new with Flume and I'd like to use it to get a stable flow of data
> to my database (To be able to handle rush hours by delaying the write in
> database, without introducing any timeout or latency to the user).
> >
> > My questions are :
> >
> > What is the best way to create the log file that will be used as source
> for flume ?
> >
> > Our production environment is running apache servers and php scripts.
> > I can't just use access log because some informations are stored in
> session, so I need to build a custom source.
> > An other point is that writing a file seems to be primitive and not
> really efficient since it writes the disk instead of writing the memory for
> any event I store (many events every second).
> >
> > How to use this system (as Facebook does with scribe) to proceed
> real-time analytics ?
> >
> > I'm open to here about hdfs, hbase or whatever could help reaching my
> goals which are a stable flow to the database and near real-time analytics
> (seconds to minutes).
> >
> > Thanks for your help.
> >
> > Alain
> >
> >

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