Ordering of Records in Stream

Question

Here are some of the queries I have :

I have two different streams stream1 and stream2 in which the elements are in order.

1) Now

Answer 1

1) Yes and no. Flink uses so-called Watermarks to track the ordering. This ensures that records can be assigned to the correct windows and windows are not closed until all data is available. However, a strict order is not guaranteed per group (because of parallel incoming data). Between groups, there is no ordering guarantee at all.

2) Basically same answer as for (1).

3) You do not need to use keyBy again. The map/flatMap will be chained by default.

4) See https://ci.apache.org/projects/flink/flink-docs-release-1.0/internals/general_arch.html#the-processes