Github user fhueske commented on the issue: https://github.com/apache/flink/pull/2332 Hi @delding, I'm sorry that I did not mention this earlier, but I just noticed that the `HBaseSink` does not implement any logic for checkpointing and fault-tolerance. The checkpointing logic of a sink and the guarantees of the external data store define what kind of emission guarantees a sink function can offer (exactly once, at-least once). In order to make this PR mergable, we need to figure out what kind of guarantees it provides under which assumptions / in which scenarios. As an example see the [documentation of the Cassandra sink](https://ci.apache.org/projects/flink/flink-docs-master/dev/connectors/cassandra.html). This is very important because users will rely on the stated guarantees. I am not very familiar with HBase and what kind of write semantics and transnational guarantees it provides. Can you describe which kind of guarantees an `HBaseSink` can achieve and how it would be integrated with Flink's Checkpointing mechanism? Thanks, Fabian
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