[
https://issues.apache.org/jira/browse/FLINK-4080?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15354779#comment-15354779
]
ASF GitHub Bot commented on FLINK-4080:
---------------------------------------
GitHub user tzulitai opened a pull request:
https://github.com/apache/flink/pull/2180
[FLINK-4080][kinesis-connector] Guarantee exactly-once for Kinesis consumer
when fail in middle of aggregated records
If multiple Kinesis records were aggregated into a single record by KPL,
when deaggregated at the consumer, all deaggregated subrecords will have the
same sequence number. This breaks the exactly-once guarantee of the
`FlinkKinesisConsumer` if it happens to fail while we are still in the middle
of processing a deaggregated records (the first record's sequence number will
incorrectly mark the whole batch of aggregated records as processed).
To fix this, this PR changes the snapshot state type of
`FlinkKinesisConsumer` from `HashMap<KinesisStreamShard, String>` to
`HashMap<KinesisStreamShard, SequenceNumber>`.
`SequenceNumber` is a new class to represent a combination of a "main
sequence number" and a "subsequence number". When the `ShardConsumerThread`
starts consuming records, we check if the last record after restore was a
aggregated record. If yes, we first handle the dangling subrecords.
@rmetzger I'm adding this change to the original Kinesis connector in
`master` instead of waiting for the big PR #2131 to be merged, because I think
this is a bug we must fix before 1.1, and I'm not sure if #2131 will be merged
before the RC for 1.1 comes out. Depending on whether #2131 or this PR gets
merged first, I'll rebase the other one accordingly.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/tzulitai/flink FLINK-4080
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/flink/pull/2180.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #2180
----
commit a9593677a4c73c9475b1e85204002d6470f2115a
Author: Gordon Tai <[email protected]>
Date: 2016-06-29T07:46:35Z
[FLINK-4080] Guarantee exactly-once for Kinesis consumer for failures in
the middle of aggregated records
----
> Kinesis consumer not exactly-once if stopped in the middle of processing
> aggregated records
> -------------------------------------------------------------------------------------------
>
> Key: FLINK-4080
> URL: https://issues.apache.org/jira/browse/FLINK-4080
> Project: Flink
> Issue Type: Sub-task
> Components: Kinesis Connector, Streaming Connectors
> Reporter: Tzu-Li (Gordon) Tai
> Assignee: Tzu-Li (Gordon) Tai
> Priority: Critical
> Fix For: 1.1.0
>
>
> I've occasionally experienced unsuccessful ManualExactlyOnceTest after
> several tries.
> Kinesis records of the same aggregated batch will have the same sequence
> number, and different sub-sequence numbers
> (http://docs.aws.amazon.com/streams/latest/dev/kinesis-kpl-consumer-deaggregation.html).
> The current code of the consumer is committing state every time it finishes
> processing a record, even de-aggregated ones. This is a bug since this will
> incorrectly mark all remaining records of the de-aggregated batch as
> processed in the state.
> Proposed fix:
> 1. Use the extended `UserRecord` class in KCL to represent all records
> (either non- or de-aggregated) instead of the basic `Record` class. This
> gives access to whether or not the record was originally aggregated.
> 2. The sequence number state we are checkpointing needs to be able to
> indicate that the last seen sequence number of a shard may be a de-aggregated
> shard, i.e., {"shard0" -> "5:8", "shard1" -> "2"} meaning the 8th sub-record
> of the 5th record was last seen for shard 0. On restore, we start again from
> record 5 for shard 0 and skip the first 7 sub-records; however, for shard 1
> we start from record 3 since record 2 is non-aggregated and already fully
> processed.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
