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Date: Thu, 4 Dec 2014 09:14:11 +0100
Message-ID: 
 <CAE6kwsNXUypfdL_BY0-1uXErG1g3dzSWbJ5JXt5-2qi25AqwMQ@mail.gmail.com>
Subject: Re: Deal with duplicates in Flume with a crash.
From: Guillermo Ortiz <konstt2000@gmail.com>
To: user@flume.apache.org
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What I don't understand it's that you are getting an UUID for sets of
1000 lines, am I right? how could you know if there're duplicates if
you are evaluating set of lines and not line per line with UUID?

I thought that what you were doing:
1.Get a line from the Source X.
2.Calculate an UUID for a single line with an interceptor
3.Another interceptor checks this UUID in HBase. If it doesn't exist,
you send to the channel and put the UUID in Hbase,

If you are grouping the lines.. aren't you checking duplicates to set level=
??

Maybe you're checking the UUID in the Sink, although I see the same
problem. Where am I wrong??

2014-12-04 0:50 GMT+01:00 Mike Keane <mkeane@conversantmedia.com>:
> I'm not sure I understand your question but I'll be the first to admit th=
is is not fool proof.
>
> That said here are a couple inherent risks I am taking.  Assume FlumeEven=
tA is one of 1000 events in a batch.  If FlumeEventA makes it to FlumeAgent=
1 but the batch fails it is entirely possible when the batch is resent it g=
oes to FlumeAgent2.  Now this event is on 2 separate file channels, separat=
e jvms and separate servers.  It is possible but extremely unlikely that Fl=
umeEventA is processed at the exact same time in FlumeAgent1 and FlumeAgent=
2.  Both agents pop the event off the channel, pull the UUID off the header=
 and check if it is in HBase.  Both do not find it so both write to HDFS an=
d we have a duplicate.  Considering the archetecture we believe the odds of=
 this are incredibly small and we are OK with the risk.
>
> Since the write to HDFS is in a transaction if it fails I don't do a HBas=
e put of the UUID, the transaction rolls back and we try again.  I did a fa=
ir amount studying the sink and bucketwriter code at the time to understand=
 what the fail conditions are when writing to HDFS.  If I remember right it=
 could fail creating the file, writing to the file, closing the file and re=
naming the file.  We all have or own SLAs to meet.  After a pretty thorough=
 review and amount of testing we were comfortable this met our SLA better t=
han a mapreduce job to dedupe 90 billion log lines per day.
>
> Joey Echeverria <joey@cloudera.com> wrote:
>
>
> What happens if the write to HDFS succeeds before the HBase put?
>
> -Joey
>
> On Wed, Dec 3, 2014 at 2:35 PM, Mike Keane <mkeane@conversantmedia.com> w=
rote:
>> We effectively mitigated this problem by using the UUID interceptor and =
customizing the HDFS Sink to do a check and put of the UUID to HBase.  In t=
he customized sink we check HBase to see if we have seen the UUID before, i=
f we have it is a duplicate and we log a new duplicate metric with the exis=
ting sink metrics and throw the event away.  If we have not seen the UUID b=
efore we write the Event to HDFS and do a put of the UUID to hbase.
>>
>> Because of our volume to minimize the number of check/puts to HBase we p=
ut multiple logs in a single FlumeEvent.
>>
>>
>> -Mike
>>
>> ________________________________________
>> From: Guillermo Ortiz [konstt2000@gmail.com]
>> Sent: Wednesday, December 03, 2014 4:15 PM
>> To: user@flume.apache.org
>> Subject: Re: Deal with duplicates in Flume with a crash.
>>
>> I didn't know anything about a Hive Sink, I'll check the JIRA about it, =
thanks.
>> The pipeline is Flume-Kafka-SparkStreaming-XXX
>>
>> So I guess I should deal in SparkStreaming with it, right? I guess
>> that it would be easy to do it with an UUID interceptor or is there
>> another way easier?
>>
>> 2014-12-03 22:56 GMT+01:00 Roshan Naik <roshan@hortonworks.com>:
>>> Using the UUID interceptor at the source closest to data origination.. =
it
>>> will help identify duplicate events after they are delivered.
>>>
>>> If it satisfies your use case, the upcoming Hive Sink will mitigate the
>>> problem a little bit (since it uses transactions to write to destinatio=
n).
>>>
>>> -roshan
>>>
>>>
>>> On Wed, Dec 3, 2014 at 8:44 AM, Joey Echeverria <joey@cloudera.com> wro=
te:
>>>>
>>>> There's nothing built into Flume to deal with duplicates, it only
>>>> provides at-least-once delivery semantics.
>>>>
>>>> You'll have to handle it in your data processing applications or add
>>>> an ETL step to deal with duplicates before making data available for
>>>> other queries.
>>>>
>>>> -Joey
>>>>
>>>> On Wed, Dec 3, 2014 at 5:46 AM, Guillermo Ortiz <konstt2000@gmail.com>
>>>> wrote:
>>>> > Hi,
>>>> >
>>>> > I would like to know if there's a easy way to deal with data
>>>> > duplication when an agent crashs and it resends same data again.
>>>> >
>>>> > Is there any mechanism to deal with it in Flume,
>>>>
>>>>
>>>>
>>>> --
>>>> Joey Echeverria
>>>
>>>
>>>
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>
>
>
> --
> Joey Echeverria
>
>
>
>
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