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From Robert Metzger <rmetz...@apache.org>
Subject Re: Flink recovery
Date Tue, 17 May 2016 11:58:59 GMT
Hi Naveen,

I think cancelling a job is not the right approach for testing our
exactly-once guarantees. By cancelling a job, you are discarding the state
of your job. Restarting from scratch (without using a savepoint) will cause
duplicates.
What you can do to validate the behavior is randomly killing a task manager
running your job. Then, the job should restart on the remaining machines
(make sure that enough slots are available even after the failure) and you
shouldn't have any duplicates in HDFS.

Regards,
Robert





On Tue, May 17, 2016 at 11:27 AM, Stephan Ewen <sewen@apache.org> wrote:

> Hi Naveen!
>
> I assume you are using Hadoop 2.7+? Then you should not see the
> ".valid-length" file.
>
> The fix you mentioned is part of later Flink releases (like 1.0.3)
>
> Stephan
>
>
> On Mon, May 16, 2016 at 11:46 PM, Madhire, Naveen <
> Naveen.Madhire@capitalone.com> wrote:
>
>> Thanks Fabian. Actually I don’t see a .valid-length suffix file in the
>> output HDFS folder.
>> Can you please tell me how would I debug this issue or do you suggest
>> anything else to solve this duplicates problem.
>>
>>
>> Thank you.
>>
>> From: Fabian Hueske <fhueske@gmail.com>
>> Reply-To: "user@flink.apache.org" <user@flink.apache.org>
>> Date: Saturday, May 14, 2016 at 4:10 AM
>> To: "user@flink.apache.org" <user@flink.apache.org>
>> Subject: Re: Flink recovery
>>
>> The behavior of the RollingFileSink depends on the capabilities of the
>> file system.
>> If the file system does not support to truncate files such as older HDFS
>> versions, an additional file with a .valid-length suffix is written to
>> indicate how much of the file is valid.
>> All records / data that come after the valid-length are duplicates.
>> Please refer to the JavaDocs of the RollingFileSink for details [1].
>>
>> If the .valid-length file does not solve the problem, you might have
>> found a bug and we should have a closer look at the problem.
>>
>> Best, Fabian
>>
>> [1]
>> https://ci.apache.org/projects/flink/flink-docs-master/api/java/org/apache/flink/streaming/connectors/fs/RollingSink.html
>>
>> 2016-05-14 4:17 GMT+02:00 Madhire, Naveen <Naveen.Madhire@capitalone.com>
>> :
>>
>>> Thanks Fabian. Yes, I am seeing few records more than once in the output.
>>> I am running the job and canceling it from the dashboard, and running
>>> again. And using different HDFS file outputs both the times. I was thinking
>>> when I cancel the job, it’s not doing a clean cancel.
>>> Is there anything else which I have to use to make it exactly once in
>>> the output?
>>>
>>> I am using a simple read from kafka, transformations and rolling file
>>> sink pipeline.
>>>
>>>
>>>
>>> Thanks,
>>> Naveen
>>>
>>> From: Fabian Hueske <fhueske@gmail.com>
>>> Reply-To: "user@flink.apache.org" <user@flink.apache.org>
>>> Date: Friday, May 13, 2016 at 4:26 PM
>>>
>>> To: "user@flink.apache.org" <user@flink.apache.org>
>>> Subject: Re: Flink recovery
>>>
>>> Hi Naveen,
>>>
>>> the RollingFileSink supports exactly-once output. So you should be good.
>>>
>>> Did you see events being emitted multiple times (should not happen with
>>> the RollingFileSink) or being processed multiple times within the Flink
>>> program (might happen as explained before)?
>>>
>>> Best, Fabian
>>>
>>> 2016-05-13 23:19 GMT+02:00 Madhire, Naveen <
>>> Naveen.Madhire@capitalone.com>:
>>>
>>>> Thank you Fabian.
>>>>
>>>> I am using HDFS rolling sink. This should support the exactly once
>>>> output in case of failures, isn’t it? I am following the below
>>>> documentation,
>>>>
>>>>
>>>> https://ci.apache.org/projects/flink/flink-docs-master/apis/streaming/fault_tolerance.html#fault-tolerance-guarantees-of-data-sources-and-sinks
>>>>
>>>> If not what other Sinks can I use to have the exactly once output since
>>>> getting exactly once output is critical for our use case.
>>>>
>>>>
>>>>
>>>> Thanks,
>>>> Naveen
>>>>
>>>> From: Fabian Hueske <fhueske@gmail.com>
>>>> Reply-To: "user@flink.apache.org" <user@flink.apache.org>
>>>> Date: Friday, May 13, 2016 at 4:13 PM
>>>> To: "user@flink.apache.org" <user@flink.apache.org>
>>>> Subject: Re: Flink recovery
>>>>
>>>> Hi,
>>>>
>>>> Flink's exactly-once semantics do not mean that events are processed
>>>> exactly-once but that events will contribute exactly-once to the state of
>>>> an operator such as a counter.
>>>> Roughly, the mechanism works as follows:
>>>> - Flink peridically injects checkpoint markers into the data stream.
>>>> This happens synchronously across all sources and markers.
>>>> - When an operator receives a checkpoint marker from all its sources,
>>>> it checkpoints its state and forwards the marker
>>>> - When the marker was received by all sinks, the distributed checkpoint
>>>> is noted as successful.
>>>>
>>>> In case of a failure, the state of all operators is reset to the last
>>>> successful checkpoint and the sources are reset to the point when the
>>>> marker was injected.
>>>> Hence, some events are sent a second time to the operators but the
>>>> state of the operators was reset as well. So the repeated events contribute
>>>> exactly once to the state of an operator.
>>>>
>>>> Note, you need a SinkFunction that supports Flink's checkpointing
>>>> mechanism to achieve exactly-once output. Otherwise, it might happen that
>>>> results are emitted multiple times.
>>>>
>>>> Cheers, Fabian
>>>>
>>>> 2016-05-13 22:58 GMT+02:00 Madhire, Naveen <
>>>> Naveen.Madhire@capitalone.com>:
>>>>
>>>>> I checked the JIRA and looks like FLINK-2111 should address the issue
>>>>> which I am facing. I am canceling the job from dashboard.
>>>>>
>>>>> I am using kafka source and HDFS rolling sink.
>>>>>
>>>>> https://issues.apache.org/jira/browse/FLINK-2111
>>>>>
>>>>> Is this JIRA part of Flink 1.0.0?
>>>>>
>>>>>
>>>>>
>>>>> Thanks,
>>>>> Naveen
>>>>>
>>>>> From: "Madhire, Venkat Naveen Kumar Reddy" <
>>>>> Naveen.Madhire@capitalone.com>
>>>>> Reply-To: "user@flink.apache.org" <user@flink.apache.org>
>>>>> Date: Friday, May 13, 2016 at 10:58 AM
>>>>> To: "user@flink.apache.org" <user@flink.apache.org>
>>>>> Subject: Flink recovery
>>>>>
>>>>> Hi,
>>>>>
>>>>> We are trying to test the recovery mechanism of Flink with Kafka and
>>>>> HDFS sink during failures.
>>>>>
>>>>> I’ve killed the job after processing some messages and restarted the
>>>>> same job again. Some of the messages I am seeing are processed more than
>>>>> once and not following the exactly once semantics.
>>>>>
>>>>>
>>>>> Also, using the checkpointing mechanism and saving the state
>>>>> checkpoints into HDFS.
>>>>> Below is the checkpoint code,
>>>>>
>>>>> envStream.enableCheckpointing(11);
>>>>> envStream.getCheckpointConfig().setCheckpointingMode(CheckpointingMode.EXACTLY_ONCE);
>>>>> envStream.getCheckpointConfig().setCheckpointTimeout(60000);
>>>>> envStream.getCheckpointConfig().setMaxConcurrentCheckpoints(4);
>>>>>
>>>>> envStream.setStateBackend(new FsStateBackend("hdfs://ipaddr/mount/cp/checkpoint/"));
>>>>>
>>>>>
>>>>> One thing I’ve noticed is lowering the time to checkpointing is
>>>>> actually lowering the number of messages processed more than once and
11ms
>>>>> is the lowest I can use.
>>>>>
>>>>> Is there anything else I should try to have exactly once message
>>>>> processing functionality.
>>>>>
>>>>> I am using Flink 1.0.0 and kafka 0.8
>>>>>
>>>>>
>>>>> Thank you.
>>>>>
>>>>> ------------------------------
>>>>>
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>>>>> The information contained in this e-mail is confidential and/or
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>>>>> transmitted herewith is intended only for use by the individual or entity
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>>>>
>>>>
>>>> ------------------------------
>>>>
>>>> The information contained in this e-mail is confidential and/or
>>>> proprietary to Capital One and/or its affiliates and may only be used
>>>> solely in performance of work or services for Capital One. The information
>>>> transmitted herewith is intended only for use by the individual or entity
>>>> to which it is addressed. If the reader of this message is not the intended
>>>> recipient, you are hereby notified that any review, retransmission,
>>>> dissemination, distribution, copying or other use of, or taking of any
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>>>> have received this communication in error, please contact the sender and
>>>> delete the material from your computer.
>>>>
>>>
>>>
>>> ------------------------------
>>>
>>> The information contained in this e-mail is confidential and/or
>>> proprietary to Capital One and/or its affiliates and may only be used
>>> solely in performance of work or services for Capital One. The information
>>> transmitted herewith is intended only for use by the individual or entity
>>> to which it is addressed. If the reader of this message is not the intended
>>> recipient, you are hereby notified that any review, retransmission,
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>>> have received this communication in error, please contact the sender and
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>>
>>
>> ------------------------------
>>
>> The information contained in this e-mail is confidential and/or
>> proprietary to Capital One and/or its affiliates and may only be used
>> solely in performance of work or services for Capital One. The information
>> transmitted herewith is intended only for use by the individual or entity
>> to which it is addressed. If the reader of this message is not the intended
>> recipient, you are hereby notified that any review, retransmission,
>> dissemination, distribution, copying or other use of, or taking of any
>> action in reliance upon this information is strictly prohibited. If you
>> have received this communication in error, please contact the sender and
>> delete the material from your computer.
>>
>
>

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