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From Robert Metzger <rmetz...@apache.org>
Subject Re: Kafka partition alignment for event time
Date Thu, 25 Feb 2016 08:50:56 GMT
Hi Erdem,

FLINK-3440 has been resolved. The fix is merged to master. 1.0-SNAPSHOT
should already contain the fix and it'll be in 1.0.0 (for which I'll post a
release candidate today) as well.

On Thu, Feb 18, 2016 at 3:24 PM, Erdem Agaoglu <erdem.agaoglu@gmail.com>
wrote:

> Thanks Stephan
>
> On Thu, Feb 18, 2016 at 3:00 PM, Stephan Ewen <sewen@apache.org> wrote:
>
>> You are right, the checkpoints should contain all offsets.
>>
>> I created a Ticket for this:
>> https://issues.apache.org/jira/browse/FLINK-3440
>>
>>
>>
>>
>> On Thu, Feb 18, 2016 at 10:15 AM, agaoglu <erdem.agaoglu@gmail.com>
>> wrote:
>>
>>> Hi,
>>>
>>> On a related and a more exaggerated setup, our kafka-producer (flume)
>>> seems
>>> to send data to a single partition at a time and switches it every few
>>> minutes. So when i run my flink datastream program for the first time, it
>>> starts on the *largest* offsets and shows something like this:
>>>
>>> . Fetched the following start offsets [FetchPartition {partition=7,
>>> offset=15118832832}]
>>> . Fetched the following start offsets [FetchPartition {partition=1,
>>> offset=15203613236}]
>>> . Fetched the following start offsets [FetchPartition {partition=2,
>>> offset=15366811664}]
>>> . Fetched the following start offsets [FetchPartition {partition=0,
>>> offset=15393999709}]
>>> . Fetched the following start offsets [FetchPartition {partition=8,
>>> offset=15319475583}]
>>> . Fetched the following start offsets [FetchPartition {partition=5,
>>> offset=15482889767}]
>>> . Fetched the following start offsets [FetchPartition {partition=6,
>>> offset=15113885928}]
>>> . Fetched the following start offsets [FetchPartition {partition=3,
>>> offset=15182701991}]
>>> . Fetched the following start offsets [FetchPartition {partition=4,
>>> offset=15186569356}]
>>>
>>> For that instance flume happens to be sending data to partition-6 only,
>>> so
>>> other consumers sit idly. Working with default paralellism 4, only one of
>>> the 4 threads is able to source data and checkpointing logs reflect that:
>>>
>>> Committing offsets [-915623761776, -915623761776, -915623761776,
>>> -915623761776, -915623761776, -915623761776, -915623761776,
>>> -915623761776,
>>> -915623761776] to offset store: FLINK_ZOOKEEPER
>>> Committing offsets [-915623761776, -915623761776, -915623761776,
>>> -915623761776, -915623761776, -915623761776, 15114275927, -915623761776,
>>> -915623761776] to offset store: FLINK_ZOOKEEPER
>>> Committing offsets [-915623761776, -915623761776, -915623761776,
>>> -915623761776, -915623761776, -915623761776, -915623761776,
>>> -915623761776,
>>> -915623761776] to offset store: FLINK_ZOOKEEPER
>>> Committing offsets [-915623761776, -915623761776, -915623761776,
>>> -915623761776, -915623761776, -915623761776, -915623761776,
>>> -915623761776,
>>> -915623761776] to offset store: FLINK_ZOOKEEPER
>>>
>>> This also means checkpoint will only contain the offset for partition-6.
>>> So
>>> if program is stopped and restarted at a later time, it restores the
>>> offset
>>> for partition-6 only and other partitions are started at the largest
>>> offset.
>>> So it's able to process unseen data in partition-6 but not others. Say if
>>> flume produces data to partition-3 when flink program is stopped, they're
>>> lost, while the data in partition-6 is not. This generally causes
>>> multiple
>>> (late-)windows to be fired after restart, because we now generate
>>> watermarks
>>> off partition-3 which says the windows of the unseen data in partition-6
>>> are
>>> already complete.
>>>
>>> This also has a side effect of windows not triggering unless some
>>> rebalancing is done beforehand. Since only 1 of the 4 threads will source
>>> data and generate watermarks, window triggers won't get watermarks from
>>> other 3 sources and wait long past the watermarks generated from the
>>> single
>>> source.
>>>
>>> I know producers shouldn't work like that, but consumers shouldn't care.
>>> I
>>> think it may also create some edge cases even if things were not as
>>> extreme
>>> as ours. If checkpoints could contain offsets of all of the partitions
>>> regardless of their contents, probably storing start offsets in first
>>> run, i
>>> guess that would solve the problems around restarting.
>>>
>>>
>>>
>>> --
>>> View this message in context:
>>> http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/Kafka-partition-alignment-for-event-time-tp4782p4998.html
>>> Sent from the Apache Flink User Mailing List archive. mailing list
>>> archive at Nabble.com.
>>>
>>
>>
>
>
> --
> erdem agaoglu
>

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