presto-main/src/main/java/io/prestosql/operator/OuterLookupSource.java/OuterLookupSourceSupplier/getLookupSource
class OuterLookupSourceSupplier:        @Override
        public LookupSource getLookupSource()
        {
            return new OuterLookupSource(lookupSourceSupplier.get(), outerPositionTracker);
        }