tiflash explain analyze actRows is zero unexpectly

[guo-shaoge]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. load tpch50 dataset(may be other smaller dataset is also ok)
2. run sql:

set @@tidb_isolation_read_engines = 'tiflash';
explain analyze select * from lineitem inner join orders on lineitem.l_orderkey = orders.o_orderkey limit 1000;

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

actRow is not zero

3. What did you see instead (Required)

actRows of tiflash executor is zero.

4. What is your TiDB version? (Required)

MySQL [test]> select tidb_version();
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version()                                                                                                                                                                                                                                                     |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v7.6.0-alpha-602-gfbe232e3f8
Edition: Community
Git Commit Hash: fbe232e3f85d1c173ad15fe2401c09af4b1424de
Git Branch: HEAD
UTC Build Time: 2024-01-16 05:14:57
GoVersion: go1.21.0
Race Enabled: false
Check Table Before Drop: false
Store: tikv |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.044 sec)

[guo-shaoge]

looks like coord doesn't handle Limit that in tidb. check https://github.com/pingcap/tidb/blob/master/pkg/executor/internal/mpp/local_mpp_coordinator.go#L336

Only happens when limit doesn't push down to tiflash