wuchong commented on issue #8678: [FLINK-12708][table] Introduce new source and sink interfaces to make Blink runner work URL: https://github.com/apache/flink/pull/8678#issuecomment-501128458 Hi @aljoscha , Thanks very much for the suggestions. Regarding to the `TableStats`. The `TableStats` is the statistics of a table (e.g. row count, ndv, max/min...). It is important information during optimization and is important for the performance improvement of TP-CDS. The `TableStats` was already there but didn't work with `TableSource`. So we expose the `TableStats` in `TableSource`, to support reporting statistics for a table source in this PR. Regarding to the name of `LookupableTableSource`, do you think the `lookupable` is not appropriate? We use the lookup terminology in Blink runner including lookup join, lookup function, lookup tablesource. If we use `QueryableTableSource` it might be not align with other terminologies. And we add a `able` suffix to `lookup` to indicate it is a table source which has the ability to lookup, similar to `FilterableTableSource`. Regarding to the only one `getLookupFunction()`, I'm afraid we can't, because `AsyncTableFunction` doesn't extend `TableFunction`. The same super interface is `UserDefinedFunction`. But IMO, returning a `UserDefinedFunction` is not appropriate here. I have an idea to make the interface only have one method. That is introuding a `LookupFunctionProvider`. I have created a gist for this idea: https://gist.github.com/wuchong/78fa3fa40323543aac8297fbecae09d8. What do you think about this? Regarding to how to implement a lookup function, yes, it is not clear in the Javadoc. Because lookup join uses `TableFunction` as a lookup function, the `TableFunction` is not just used as lookup. So we may can't add the lookup function implementation details to the Javadoc of `TableFunction`. I will add some more instruction to the Javadoc of `getLookupFunction()` and also the documentation with example in the future.
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