Major Description
In certain cases (e.g M --> R --> R), if the parent vertex has 0 tasks tez currently does not modify the parallelism factor in downstream.
e.g
SELECT ss_store_sk,
ss_sold_date_sk,
ss_quantity,
ss_sales_price,
LEAD(ss_sales_price, 1) OVER(PARTITION BY ss_store_sk
ORDER BY ss_quantity)
FROM store_sales
WHERE ss_sold_date_sk IS NOT NULL
AND ss_quantity IS NOT NULL
AND ss_sales_price > 2857684
AND ss_sales_price < 2857685
AND ss_store_sk > 10234233423
AND ss_store_sk < 20234234324
ORDER BY ss_store_sk,
ss_sold_date_sk;
This would launch DAG "M1 (0) --> R2 (156) --> R3 (1)". However, R2 retains the parallelism of 156 even though no output would be generated in M1.
