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Flume, mail # user - hdfs.idleTimeout ,what's it used for ?


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Re: hdfs.idleTimeout ,what's it used for ?
Connor Woodson 2013-01-18, 02:20
@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 <[EMAIL PROTECTED]>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 <
> [EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]>
>>> 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