mjsax commented on code in PR #13496:
URL: https://github.com/apache/kafka/pull/13496#discussion_r1158814912
##########
streams/src/main/java/org/apache/kafka/streams/kstream/internals/KTableKTableInnerJoin.java:
##########
@@ -153,11 +154,37 @@ public void init(final ProcessorContext<?, ?> context) {
@Override
public ValueAndTimestamp<VOut> get(final K key) {
- final ValueAndTimestamp<V1> valueAndTimestamp1 =
valueGetter1.get(key);
+ return computeJoin(key, valueGetter1::get, valueGetter2::get);
+ }
+
+ @Override
+ public ValueAndTimestamp<VOut> get(final K key, final long
asOfTimestamp) {
Review Comment:
Wondering if this is correct? This "ValueGetter" queries the
(non-materialized) result table of in inner-join, and re-computes the result
on-the-fly? Maybe it will get clear in a follow up PR, but would love to get a
short / high-level explanation why it's the right thing to do (as I right now
don't understand it).
What I am worried about it the case, that we don't update the result for
out-of-order updates, but when we re-compute the result on the fly, we might
re-compute an "updated" result, and thus don't return the same record as
perviously emitted.
You call this out in the second example of the "Proposal" section on the KIP:
```
A: (timestamp = 0, value = a0)
B: (timestamp = 2, value = b2) -> latest record on B side, emits (a0, b2)
with timestamp=2
A: (timestamp = 5, value = a5) -> latest record on A side, emits (a5, b2)
with timestamp=5
A: (timestamp = 1, value = a1) -> out-of-order record on A side, no new join
result emitted. the older (a0, b2) join result is no longer correct.
```
We don't emit anything for the last record, while the older join result
becomes invalid (that's ok); but if we call `get(key,1)` later, would we get
back the older (not updated) `(a2,b0)` (which would be correct to return from a
consistency point of view because the value-getter should return the same thing
as if the result state-store would have been materialized, and the value-getter
is not in use), or would we get back a now updated result `(a1,b2)`?
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