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From Connor Woodson <cwoodson....@gmail.com>
Subject Re: hdfs.idleTimeout ,what's it used for ?
Date Fri, 18 Jan 2013 02:19:31 GMT
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> 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>
>> 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> 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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