presto-main/src/main/java/io/prestosql/operator/PartitionedLookupSource.java/PartitionedLookupSource/PartitionedLookupOuterPositionIterator
class PartitionedLookupSource:        public PartitionedLookupOuterPositionIterator(LookupSource[] lookupSources, boolean[][] visitedPositions)
        {
            this.lookupSources = lookupSources;
            this.visitedPositions = visitedPositions;
        }