Hi Tommy, I believe there is a way to make this work currently, but with lots of caveats and constraints.
This assumes you want to avoid any network shuffle. 1. Both topics have names that return the same value for ((topicName.hashCode() * 31) & 0x7FFFF) % parallelism. 2. Both topics have the same number of partitions. 3. The parallelism of your join function exactly matches the number of partitions. 4. You can’t change any of the above without losing state. 5. You don’t need stateful timers. If the above is true, then you could use a CoFlatMapFunction and operator state to implement a stateful join. If it’s something like a left outer join without any state TTL or need to keep both sides in state, then it’s pretty easy. — Ken PS - it’s pretty easy to figure out a “-xxx” value to append to a topic name to get the hashCode() result you need. > On Mar 3, 2023, at 4:56 PM, Tommy May <tvma...@gmail.com> wrote: > > Hello, > > My team has a Flink streaming job that does a stateful join across two high > throughput kafka topics. This results in a large amount of data ser/de and > shuffling (about 1gb/s for context). We're running into a bottleneck on this > shuffling step. We've attempted to optimize our flink configuration, join > logic, scale out the kafka topics & flink job, and speed up state access. > What we see is that the join step causes backpressure on the kafka sources > and lag slowly starts to accumulate. > > One idea we had to optimize this is to pre-partition the data in kafka on the > same key that the join is happening on. This'll effectively reduce data > shuffling to 0 and remove the bottleneck that we're seeing. I've done some > research into the topic and from what I understand this is not > straightforward to take advantage of in Flink. It looks to be a fairly > commonly requested feature based on the many StackOverflow posts and slack > questions, and I noticed there is FLIP-186 which attempts to address this > topic as well. > > Are there any upcoming plans to add this feature to a future Flink release? I > believe it'd be super impactful for similar large scale jobs out there. I'd > be interested in helping as well, but admittedly I'm relatively new to Flink. > I poked around the code a bit, and it certainly did not seem like a > straightforward addition, so it may be best handled by someone with more > internal knowledge. > > Thanks, > Tommy -------------------------- Ken Krugler http://www.scaleunlimited.com Custom big data solutions Flink, Pinot, Solr, Elasticsearch
