presto-main/src/main/java/io/prestosql/operator/SimplePagesHashStrategy.java/SimplePagesHashStrategy/hashRow
class SimplePagesHashStrategy:    @Override
    public long hashRow(int position, Page page)
    {
        long result = 0;
        for (int i = 0; i < hashChannels.size(); i++) {
            int hashChannel = hashChannels.get(i);
            Type type = types.get(hashChannel);
            Block block = page.getBlock(i);
            result = result * 31 + TypeUtils.hashPosition(type, block, position);
        }
        return result;
    }