mjsax commented on code in PR #13496:
URL: https://github.com/apache/kafka/pull/13496#discussion_r1163195888
##########
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:
> The first option is nice in that now stream-(table-table) and
(stream-table)-table joins with no intermediate materialization produce the
same results,
But are both joins really the same if the intermediate table-table result is
not materialized? Semantically, the intermediate table-table result is a
non-versioned store, and thus we cannot do a lookup into the history of it, ie,
we have a stream-tsTable join. The second query is two `stream-vTable` joins so
it seems ok if they produce different results?
> but it's also confusing because stream-(table-table) produces different
results if the user materializes the result of the table-table join as a
versioned store (which is wrong).
I don't see it as confusing (it might be very subtle to be fair...) -- the
intermediate result of a non-materialized t-t-join is semantically a tsTable
(or course, it does not get out-of-order updates, because the _join_ that
computes it has two versioned tables as input and thus drop out-of-order
updates) -- if the intermediate result is materialized as tsKV-store, semantics
should not change. If one materialized it as vKV store though, it seem ok that
semantics change, because the semantics of the intermediate result change from
being non-versioned to versioned, and thus the join changed from
`stream-tsTable` to `stream-vTable`.
My point is, that for a table-table join, there are 4 entities: both input
tables, the join operator, plus the result table. The two input table (v-table
vs ts-table) determine what join operator we pick (ie, drop out-of-order
updates yes/no), and the join produces an result that we know feed into the
result table with it's own semantics (by default, ts-semantics, not
v-semantics) -- Of course, depending on the used join semantics, we apply
different updates to the table, but we don't change the table semantics itself.
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