AsyncFunctionHi Seed, I think the back pressure should emerge by blocking the AsyncFunction.asyncInvoke call. So it depends on how ResultFuture is generated from Cassandra client whether it blocks on submitting request or not when the number of pending requests is too big. Maybe, AsyncFunction.asyncInvoke needs addition throttling on submitting requests to Cassandra. See also [1] for Cassandra sink with throttling.
Best, Andrey [1] https://issues.apache.org/jira/browse/FLINK-9083 On Tue, Mar 19, 2019 at 3:48 AM Seed Zeng <seed.z...@klaviyo.com> wrote: > Flink Version - 1.6.1 > > In our application, we consume from Kafka and sink to Cassandra in the > end. We are trying to introduce a custom async function in front of the > Sink to carry out some customized operations. In our testing, it appears > that the Async function is not generating backpressure to slow down our > Kafka Source when Cassandra becomes unhappy. Essentially compared to an > almost identical job where the only difference is the lack of the Async > function, Kafka source consumption speed is much higher under the same > settings and identical Cassandra cluster. The experiment is like this. > > Job 1 - without async function in front of Cassandra > Job 2 - with async function in front of Cassandra > > Job 1 is backpressured because Cassandra cannot handle all the writes and > eventually slows down the source rate to 6.5k/s. > Job 2 is slightly backpressured but was able to run at 14k/s. > > Is the AsyncFunction somehow not reporting the backpressure correctly? > > Thanks, > Seed >
