presto-main/src/main/java/io/prestosql/operator/PartitionedLookupSource.java/OuterPositionTracker/Factory
class OuterPositionTracker:            public Factory(List<Supplier<LookupSource>> partitions)
            {
                this.lookupSources = partitions.stream()
                        .map(Supplier::get)
                        .toArray(LookupSource[]::new);

                visitedPositions = Arrays.stream(this.lookupSources)
                        .map(LookupSource::getJoinPositionCount)
                        .map(Math::toIntExact)
                        .map(boolean[]::new)
                        .toArray(boolean[][]::new);
            }