asereda-gs commented on a change in pull request #1101: [CALCITE-2909] Optimize
Enumerable SemiJoin with lazy computation of innerLookup (Ruben Quesada Lopez)
URL: https://github.com/apache/calcite/pull/1101#discussion_r268158421
##########
File path:
linq4j/src/main/java/org/apache/calcite/linq4j/EnumerableDefaults.java
##########
@@ -1298,11 +1298,11 @@ private void closeInner() {
final EqualityComparer<TKey> comparer) {
return new AbstractEnumerable<TSource>() {
public Enumerator<TSource> enumerator() {
- final Enumerable<TKey> innerLookup =
- comparer == null
- ? inner.select(innerKeySelector).distinct()
- : inner.select(innerKeySelector).distinct(comparer);
-
+ // CALCITE-2909 Delay the computation of the innerLookup until the
moment when we are sure
+ // that it will be really needed, i.e. when the first outer enumerator
item is processed
+ final Enumerable<TKey> innerLookup = comparer == null
+ ? Linq4j.lazyEnumerable(() ->
inner.select(innerKeySelector).distinct())
+ : Linq4j.lazyEnumerable(() ->
inner.select(innerKeySelector).distinct(comparer));
Review comment:
Originally I was guided by the fact that it is nicer (from API perspective)
to use `T` (which may be lazy) rather than explicitly define `Lazy<T>`. Some
examples:
1.
[Supplier.memoize](https://google.github.io/guava/releases/19.0/api/docs/com/google/common/base/Suppliers.html#memoize(com.google.common.base.Supplier))
from guava.
2.
[StreamSupport.stream(Supplier<Spliterator>)](https://docs.oracle.com/javase/8/docs/api/java/util/stream/StreamSupport.html#stream-java.util.function.Supplier-int-boolean-)
3.
[Observable.defer](http://reactivex.io/RxJava/javadoc/rx/Observable.html#defer-rx.functions.Func0-)
I'm sorry if I have wasted your time @rubenada . This change looks fine. Pls
rebase and I'll merge it after 1.19 release.
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