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From Connor Woodson <cwoodson....@gmail.com>
Subject Re: hdfs.idleTimeout ,what's it used for ?
Date Fri, 18 Jan 2013 03:24:04 GMT
The way idleTimeout works right now is that it's another rollInterval; it
will work best when rollInterval is not set and so it seems that it's use
is best for when you don't want to use a rollInterval and just want to have
your bucketwriters close when no events are coming through (caused by path
change or something else; and you can still roll reliably with either count
or size)

As such, perhaps it is more clear if idleTimeout is renamed to idleRoll or
such?

And then change idleTimeout to only count seconds since it was closed; if a
bucketwriter is closed for long enough it will automatically remove itself.
This type of idle will then work well with rollInterval, while the other
one doesn't (idleRoll + rollInterval creates two time-based rollers. There
are certainly times for that, but not all of the time).

- Connor


On Thu, Jan 17, 2013 at 6:46 PM, Juhani Connolly <
juhani_connolly@cyberagent.co.jp> wrote:

>  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.
>
> @Mohit:
>
> 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>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} 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>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> 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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