I'm trying to understand when will Flink's Stream Barrier (for checkpoint) be emitted by the join operator.
Consider a query like - select * from stream_1 a1 INNER JOIN stream_2 a2 on a2.orderId = a1.orderId group by HOP(a1.proctime, INTERVAL '1' HOUR, INTERVAL '1' DAY), a1.restaurantId Since I'm using a Hopping window on 1 day here, Flink will have to cache my entire 1 day events. The join operator will receive stream barrier from the previous operator. Join operator will emit one stream barrier but I'm not sure on what basis and when will it be emitted. Any help will be appreciated. Thanks! >From Flink's documentation - ```A core element in Flink’s distributed snapshotting are the stream barriers. These barriers are injected into the data stream and flow with the records as part of the data stream. The point where the barriers for snapshot n are injected (let’s call it Sn) is the position in the source stream up to which the snapshot covers the data. The barriers then flow downstream. When an intermediate operator has received a barrier for snapshot n from all of its input streams, it emits a barrier for snapshot n into all of its outgoing streams. Once a sink operator (the end of a streaming DAG) has received the barrier n from all of its input streams, it acknowledges that snapshot n to the checkpoint coordinator. After all sinks have acknowledged a snapshot, it is considered completed.``` -- Sent from: http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/
