Hi all. I’m migrating a

KeyedProcessFunction

to use async state v2 and I have a question about execution order since it’s not super explicit in the documentation here . My function does a read-modify-write. It receives a session from the sessionState, then reads the state, and merges the current session with the new session and then updates the state.

sessionState.asyncValue()
.thenApply(current -> {
    if (current == null) current = new FullSessionMessage();
    return current;
})
.thenAccept(current -> {
    current.merge(value);
    sessionState.asyncUpdate(current);
});

The docs state: “The execution order of user code entry flatMap for same-key elements are invoked strictly in order of element arrival.” Assume I have 2 elements, A and B, with A coming before B. Does this mean element A’s full chain (callbacks +

asyncUpdate

) finishes before element B’s

KeyedProcessFunction

starts, when they share the same key? Cross-key parallelism & concurrency is obviously expected and welcome, but same-key would cause issues. Thank you! tldr; Basically worried about the classic race condition in async V2 state in keyed states in the same stream: 1. A reads state X 2. B also reads state X (before A wrote back) 3. A writes X+A 4. B writes X+B → A’s merge is lost Expected result is X + A + B