Jark Wu created FLINK-14540:
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Summary: Rethink of TableSource#explainSource()
Key: FLINK-14540
URL: https://issues.apache.org/jira/browse/FLINK-14540
Project: Flink
Issue Type: Improvement
Components: Table SQL / API
Reporter: Jark Wu
In FLINK-12399 and FLINK-14132, the returned String of
{{TableSource#explainSource}} is used as part of digest of {{TableScan}}. User
have to give the correct digest for projectable or filterable or limitable
sources when pushdown has been tried. They have to overwrite
{{TableSource#explainSource()}} to reflect such changes.
However, I have some concerns about this:
1) such important restriction is not mentioned in the Javadoc of
{{TableSource#explainSource()}}, {{ProjectableTableSouce}} and
{{FilterableTableSource}}.
2) It pushes some dirty work to users which can be done by the framework, it
makes connectors more difficult to be developed **correctly** (by reflecting
all the push-downed information correctly).
3) the explainTerm/digest format of source maybe not unified and fully
described.
Regarding how to generate digest by planner, I think we can put the push-downed
information in {{TableSourceTable}} (e.g. we already put {{selectedFields}} in
it), and generate the digest using {{TableSourceTable}}.
But I may miss something that we have to push the changes to explainSource. We
can discuss this under this JIRA issue.
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