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https://issues.apache.org/jira/browse/FLINK-29625?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17616934#comment-17616934
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Martijn Visser commented on FLINK-29625:
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[~jark] I think you can answer this question better then me
> Optimize changelog normalize for upsert source
> ----------------------------------------------
>
> Key: FLINK-29625
> URL: https://issues.apache.org/jira/browse/FLINK-29625
> Project: Flink
> Issue Type: Improvement
> Components: Table SQL / Planner
> Affects Versions: 1.15.2
> Reporter: Jiabao Sun
> Priority: Major
>
> Currently, Flink will add an expensive operator _changelog normalize_ to the
> source of the upsert changelog mode to complete the _update_before_ value.
> Even inserting directly from upsert-kafka source to upsert-kafka sink will
> still add this operator, and there is an extra operator to clear
> _upsert_before_ messages, which is obviously redundant.
> In CDC scenarios, some databases do not provide update before images, such as
> Cassandra、MongoDB、TiDB({_}Old Value{_} is not turned on) and Postgres
> ({_}REPLICA IDENTITY{_} is not set to {_}FULL{_}). Using Flink SQL to process
> these changelog will have a lot of state overhead.
> I don't know much about why this operator is needed, so I take the liberty to
> ask if we can get rid of changelog normalize completely or optimistic about
> it, adding it only if a normalized changelog is required by an after operator.
> If this optimization is worthwhile, I'm happy to help with it.
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