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Posted to issues@flink.apache.org by GitBox <gi...@apache.org> on 2020/11/22 16:19:04 UTC

[GitHub] [flink] wuchong opened a new pull request #14160: [FLINK-19795][table-blink] Fix Flink SQL throws exception when changelog source contains duplicate change events

wuchong opened a new pull request #14160:
URL: https://github.com/apache/flink/pull/14160

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## What is the purpose of the change

Usually, CDC tools deliver change events to message queue in an **at-least-once** semantic. There might be duplicate INSERT/UPDATE/DELETE messages for the same primary key. However, when appling TopN query on this created source table, the TopN operator will thrown exception: `Caused by: java.lang.RuntimeException: Can not retract a non-existent record`.

We introduced a configuration `table.exec.source.cdc-events-duplicate=true|false` to indicate whether the cdc source produce duplicate messages that require the framework to deduplicate. By default, the value is false (for backward-compatibility). When it is set to true, it requires to set a primary key on the source, and the framework will this the primary key to deduplicate/normalize the changelog (using the ChangelogNormalize operator).

This option only take effect on the cdc sources which will produce full changelog, including INSERT/UPDATE_BEFORE/UPDATE_AFTER/DELETE events. So it doesn't affect the upsert sources, because upsert sources always generate a ChangelogNormalize operator after it.

This pull request also fixes FLINK-20205 to not send `UPDATE_BEFORE` messages if the downstream doesn't need it for CDC sources.

## Brief change log

- Add validation if the configuration is enabled but primary key is not defined.
- Generate ChangelogNormalize node after CDC source if `table.exec.source.cdc-events-duplicate=true`.
- Drop `UPDATE_BEFORE` messages for CDC source if downstream doesn't need it, because `ChangelogNormalize` also doesn't need the before messages.

## Verifying this change

- Added plan tests for the configuration is enabled.
- Added IT cases for the configuration is enabled.
- Added unit tests for metadata handler tests for the new `StreamExecDropUpdateBefore` node.

## Does this pull request potentially affect one of the following parts:

- Dependencies (does it add or upgrade a dependency): (yes / **no**)
- The public API, i.e., is any changed class annotated with `@Public(Evolving)`: (yes / **no**)
- The serializers: (yes / **no** / don't know)
- The runtime per-record code paths (performance sensitive): (yes / **no** / don't know)
- Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (yes / **no** / don't know)
- The S3 file system connector: (yes / **no** / don't know)

## Documentation

- Does this pull request introduce a new feature? (yes / **no**)
- If yes, how is the feature documented? (**not applicable** / docs / JavaDocs / not documented)

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