MPPTask's earier exit may cause false positive error

[windtalker]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Consider the case that
{MPPTask1, MPPTask2} =======> {MPPTask3,MPPTask4}

Assuming that MPPTask3/MPPTask4 contains executor that may cause earier exit(for example, limit and filter with always false filter condition), then MPPTask3/MPPTask4 may exit earier before consumming all the data produced by MPPTask1/MPPTask2, and once MPPTask3/MPPTask4 finish executing, it will close the exchange reciever, so if MPPTask1/MPPTask2 is sending data to MPPTask3/MPPTask4 again, it will meet closed tunnel error, if this error happens before TiDB get all the result from the query, then there is a chance that the error message will be sent to TiDB, and TiDB think the query fails, which is actually a false positive error.

2. What did you expect to see? (Required)

3. What did you see instead (Required)

4. What is your TiFlash version? (Required)

[yibin87]

Add a specific SQL and explain case here:
select asceding.item_sk from (select * from (select ss_item_sk item_sk,avg(ss_net_profit) rank_col from store_sales ss1 where ss_store_sk = 47 group by ss_item_sk having avg(ss_net_profit) > null)V1) asceding, (select * from (select ss_item_sk item_sk,avg(ss_net_profit) rank_col from store_sales ss1 group by ss_item_sk)V2) descending where asceding.item_sk = descending.item_sk;
The query plan:

The Selection_24 operator's filter is gt(Column#24, NULL), which is alwarys false.