presto-main/src/main/java/io/prestosql/operator/PartitionedLookupSource.java/PartitionedLookupSource/getNextJoinPosition
class PartitionedLookupSource:    @Override
    public long getNextJoinPosition(long currentJoinPosition, int probePosition, Page allProbeChannelsPage)
    {
        int partition = decodePartition(currentJoinPosition);
        long joinPosition = decodeJoinPosition(currentJoinPosition);
        LookupSource lookupSource = lookupSources[partition];
        long nextJoinPosition = lookupSource.getNextJoinPosition(joinPosition, probePosition, allProbeChannelsPage);
        if (nextJoinPosition < 0) {
            return nextJoinPosition;
        }
        return encodePartitionedJoinPosition(partition, toIntExact(nextJoinPosition));
    }