presto-main/src/main/java/io/prestosql/operator/LookupJoinOperator.java/JoinProcessor/tryFetchLookupSourceProvider
class JoinProcessor:        private boolean tryFetchLookupSourceProvider()
        {
            if (lookupSourceProvider == null) {
                if (!lookupSourceProviderFuture.isDone()) {
                    return false;
                }
                lookupSourceProvider = requireNonNull(getDone(lookupSourceProviderFuture));
                statisticsCounter.updateLookupSourcePositions(lookupSourceProvider.withLease(lookupSourceLease -> lookupSourceLease.getLookupSource().getJoinPositionCount()));
            }
            return true;
        }