Github user haohui commented on the issue:
https://github.com/apache/flink/pull/3712
Thanks for your pointer of the prototype!
> Do you intend to provide exactly-once guarantees for arbitrary updates?
As I think about it a little bit more, I think it might make sense to start
with the at-least-once semantic first. In practice we make the JDBC call
idempotent using `INSERT IF NOT EXISTS`.
The exactly-once part is more tricky and let's separate it out for now.
What do you think?
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