JingsongLi opened a new pull request #13914:
URL: https://github.com/apache/flink/pull/13914
## What is the purpose of the change
User requirement:
Users need to look at a few random pieces of data in a table to see what the
data looks like. So users often use the SQL:
"select * from table limit 10"
For a large table, expect to end soon because only a few pieces of data are
queried.
For DataStream or BoundedStream, they are push based execution models, so
the downstream cannot control the end of source operator.
We need push down limit to source operator, so that source operator can end
early.
Implement a LimitableBulkFormat wrapper to limit output record number in the
file source.
## Brief change log
- Introduce `LimitableBulkFormat`
- Integrate to `FileSystemTableSource`
## Verifying this change
This change is already covered by existing tests, such as
`FileSystemITCaseBase.testLimitPushDown`.
## Does this pull request potentially affect one of the following parts:
- Dependencies (does it add or upgrade a dependency): no
- The public API, i.e., is any changed class annotated with
`@Public(Evolving)`: no
- The serializers: no
- The runtime per-record code paths (performance sensitive): no
- Anything that affects deployment or recovery: JobManager (and its
components), Checkpointing, Kubernetes/Yarn/Mesos, ZooKeeper: no
- The S3 file system connector: no
## Documentation
- Does this pull request introduce a new feature? yes
- If yes, how is the feature documented? JavaDocs
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