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From Juhani Connolly <juhani_conno...@cyberagent.co.jp>
Subject Re: hdfs.idleTimeout ,what's it used for ?
Date Fri, 18 Jan 2013 02:46:04 GMT
It seemed neater at the time. It's only an issue because rollInterval 
doesn't remove the entry in sfWriters. We could change it so that close 
doesn't cancel it, and have it check whether or not the writer is 
already closed, but that'd be kind of ugly.


When flume dies unexpectedly the .tmp file remains. When it restarts 
there is some logic in HDFS sink to recover it(and continue writing from 
there). I'm not actually sure of the specifics. You may want to try and 
just kill -9 a running flume process on a test machine and then start it 
up, look at the logs and see what happens with the output.

If flume dies cleanly the file is properly closed.

On 01/18/2013 11:23 AM, Connor Woodson wrote:
> And @ my aside: I hadn't realized that the idleTimeout is canceled by 
> the rollInterval occurring. That's annoying. So setting a lower 
> idleTimeout, and drastically decreasing maxOpenFiles to at most 2 * 
> possible open files, is probably necessary.
> On Thu, Jan 17, 2013 at 6:20 PM, Connor Woodson 
> <cwoodson.dev@gmail.com <mailto:cwoodson.dev@gmail.com>> wrote:
>     @Mohit:
>     For the HDFS Sink, the tmp files are placed based on the
>     hadoop.tmp.dir property. The default location is
>     /tmp/hadoop-${user.name <http://user.name>} To change this you can
>     add -Dhadoop.tmp.dir=<path> to your Flume command line call, or
>     you can specify the property in the core-site.xml of wherever your
>     HADOOP_HOME environment variable points to.
>     - Connor
>     On Thu, Jan 17, 2013 at 6:19 PM, Connor Woodson
>     <cwoodson.dev@gmail.com <mailto:cwoodson.dev@gmail.com>> wrote:
>         Whether idleTimeout is lower or higher than rollInterval is a
>         preference; set it before, and assume you get one message
>         right on the turn of the hour, then you will have some part of
>         that hour without any bucket writers; but if you get another
>         message at the end of the hour, you will end up with two files
>         instead of one. Set it idleTimeout to be longer and you will
>         get just one file, but also (at worst case) you will have
>         twice as many bucketwriters open; so it all depends on how
>         many files you want/how much memory you have to spare.
>         - Connor
>         An aside:
>         bucketwriters, after being closed by rollInterval, aren't
>         really a memory leak; they just are very rarely useful to keep
>         around (your path could rely on hostname, and you could use a
>         rollinterval, and then those bucketwriters will still remain
>         useful). And they will get removed eventually; by default
>         after you've created your 5001st bucketwriter, the first (or
>         whichever was used longest ago) will be removed.
>         And I don't think that's the cause behind 1850 as he did have
>         an idleTimeout set at 15 minutes.
>         On Thu, Jan 17, 2013 at 6:08 PM, Juhani Connolly
>         <juhani_connolly@cyberagent.co.jp
>         <mailto:juhani_connolly@cyberagent.co.jp>> wrote:
>             It's also useful if you want files to get promptly closed
>             and renamed from the .tmp or whatever.
>             We use it with something like 30seconds setting(we have a
>             constant stream of data) and hourly bucketing.
>             There is also the issue that files closed by rollInterval
>             are never removed from the internal linkedList so it
>             actually causes a small memory leak(which can get big in
>             the long term if you have a lot of files and hourly
>             renames). I believe this is what is causing the OOM Mohit
>             is getting in FLUME-1850
>             So I personally would recommend using it(with a setting
>             that will close files before rollInterval does).
>             On 01/18/2013 06:38 AM, Bhaskar V. Karambelkar wrote:
>                 Ah I see. Again something useful to have in the flume
>                 user guide.
>                 On Thu, Jan 17, 2013 at 3:29 PM, Connor Woodson
>                 <cwoodson.dev@gmail.com
>                 <mailto:cwoodson.dev@gmail.com>> wrote:
>                     the rollInterval will still cause the last 01-17
>                     file to be closed
>                     eventually. The way the HDFS sink works with the
>                     different files is each
>                     unique path is specified by a different
>                     BucketWriter object. The sink can
>                     hold as many objects as specified by
>                     hdfs.maxOpenWorkers (default: 5000),
>                     and bucketwriters are only removed when you create
>                     the 5001th writer (5001th
>                     unique path). However, generally once a writer is
>                     closed it is never used
>                     again (all of your 1-17 writers will never be used
>                     again). To avoid keeping
>                     them in the sink's internal list of writers, the
>                     idleTimeout is a specified
>                     number of seconds in which no data is received by
>                     the BucketWriter. After
>                     this time, the writer will try to close itself and
>                     will then tell the sink
>                     to remove it, thus freeing up everything used by
>                     the bucketwriter.
>                     So the idleTimeout is just a setting to help limit
>                     memory usage by the hdfs
>                     sink. The ideal time for it is longer than the
>                     maximum time between events
>                     (capped at the rollInterval) - if you know you'll
>                     receive a constant stream
>                     of events you might just set it to a minute or
>                     something. Or if you are fine
>                     with having multiple files open per hour, you can
>                     set it to a lower number;
>                     maybe just over the average time between events.
>                     For me in just testing, I
>                     set it >= rollInterval for the cases when no
>                     events are received in a given
>                     hour (I'd rather keep the object alive for an
>                     extra hour than create files
>                     every 30 minutes or something).
>                     Hope that was helpful,
>                     - Connor
>                     On Thu, Jan 17, 2013 at 12:07 PM, Bhaskar V.
>                     Karambelkar
>                     <bhaskarvk@gmail.com <mailto:bhaskarvk@gmail.com>>
>                     wrote:
>                         Say If I have
>                         a1.sinks.k1.hdfs.path = /flume/events/%y-%m-%d/
>                         hdfs.rollInterval=60
>                         Now, if there is a file
>                         /flume/events/2013-01-17/flume_XXXXXXXXX.tmp
>                         This file is not ready to be rolled over yet,
>                         i.e. 60 seconds are not
>                         up and now it's past 12 midnight, i.e. new day
>                         And events start to be written to
>                         /flume/events/2013-01-18/flume_XXXXXXXX.tmp
>                         will the file 2013-01-17 never be rolled over,
>                         unless I have something
>                         like hdfs.idleTimeout=60  ?
>                         If so how do flume sinks keep track of files
>                         they need to rollover
>                         after idealTimeout ?
>                         In short what's the exact use of idealTimeout
>                         parameter ?

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