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https://issues.apache.org/jira/browse/FLINK-10348?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16617899#comment-16617899
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Elias Levy commented on FLINK-10348:
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[~wind_ljy]
Re: 1. The problem is timestamp alignment. Setting like fetch sizes, max
waits, etc are simply mechanism you can use to attempt to influence the rate of
processing the better align the timestamps. Those mechanism are at least one
level removed from the actual issue. It is best to address the issue directly
by attempting to align timestamp during consumption.
Re: 2. Internally the Kafka consumer behaves like a multiple input operator,
merging watermarks and messages from each partition, which it then forwards
downstream. The Kafka consumer can also selectively forward messages from the
partitions with the lowest waternark if they are available.
> Solve data skew when consuming data from kafka
> ----------------------------------------------
>
> Key: FLINK-10348
> URL: https://issues.apache.org/jira/browse/FLINK-10348
> Project: Flink
> Issue Type: New Feature
> Components: Kafka Connector
> Affects Versions: 1.6.0
> Reporter: Jiayi Liao
> Assignee: Jiayi Liao
> Priority: Major
>
> By using KafkaConsumer, our strategy is to send fetch request to brokers with
> a fixed fetch size. Assume x topic has n partition and there exists data skew
> between partitions, now we need to consume data from x topic with earliest
> offset, and we can get max fetch size data in every fetch request. The
> problem is that when an task consumes data from both "big" partitions and
> "small" partitions, the data in "big" partitions may be late elements because
> "small" partitions are consumed faster.
> *Solution: *
> I think we can leverage two parameters to control this.
> 1. data.skew.check // whether to check data skew
> 2. data.skew.check.interval // the interval between checks
> Every data.skew.check.interval, we will check the latest offset of every
> specific partition, and calculate (latest offset - current offset), then get
> partitions which need to slow down and redefine their fetch size.
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