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From "Madhire, Naveen" <Naveen.Madh...@capitalone.com>
Subject Re: Flink recovery
Date Tue, 17 May 2016 14:25:47 GMT
Hey Robert,

What is the best way to stop the streaming job in production if I want to upgrade the application
without loosing messages and causing duplicates. How can I test this scenario?
We are testing few recovery mechanisms like job failure, application upgrade and node failure.



Thanks,
Naveen

From: Robert Metzger <rmetzger@apache.org<mailto:rmetzger@apache.org>>
Reply-To: "user@flink.apache.org<mailto:user@flink.apache.org>" <user@flink.apache.org<mailto:user@flink.apache.org>>
Date: Tuesday, May 17, 2016 at 6:58 AM
To: "user@flink.apache.org<mailto:user@flink.apache.org>" <user@flink.apache.org<mailto:user@flink.apache.org>>
Subject: Re: Flink recovery

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<mailto: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<mailto: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<mailto:fhueske@gmail.com>>
Reply-To: "user@flink.apache.org<mailto:user@flink.apache.org>" <user@flink.apache.org<mailto:user@flink.apache.org>>
Date: Saturday, May 14, 2016 at 4:10 AM
To: "user@flink.apache.org<mailto:user@flink.apache.org>" <user@flink.apache.org<mailto: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<mailto: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<mailto:fhueske@gmail.com>>
Reply-To: "user@flink.apache.org<mailto:user@flink.apache.org>" <user@flink.apache.org<mailto:user@flink.apache.org>>
Date: Friday, May 13, 2016 at 4:26 PM

To: "user@flink.apache.org<mailto:user@flink.apache.org>" <user@flink.apache.org<mailto: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<mailto: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<mailto:fhueske@gmail.com>>
Reply-To: "user@flink.apache.org<mailto:user@flink.apache.org>" <user@flink.apache.org<mailto:user@flink.apache.org>>
Date: Friday, May 13, 2016 at 4:13 PM
To: "user@flink.apache.org<mailto:user@flink.apache.org>" <user@flink.apache.org<mailto: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<mailto: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<mailto:Naveen.Madhire@capitalone.com>>
Reply-To: "user@flink.apache.org<mailto:user@flink.apache.org>" <user@flink.apache.org<mailto:user@flink.apache.org>>
Date: Friday, May 13, 2016 at 10:58 AM
To: "user@flink.apache.org<mailto:user@flink.apache.org>" <user@flink.apache.org<mailto: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 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
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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
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If you have received this communication in error, please contact the sender and delete the
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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.
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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
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