HashAgg called by apply may hang forever.

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Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
   If possible, provide a recipe for reproducing the error.

create table test (a int);
insert into test value(1);
mysql> select @@tidb_hashagg_final_concurrency ;
+----------------------------------+
| @@tidb_hashagg_final_concurrency |
+----------------------------------+
| 4                                |
+----------------------------------+
1 row in set (0.00 sec)

mysql> desc select /*+ hash_agg() */ sum(a), (select NULL from test where tt.a = test.a limit 1),(select NULL from test where tt.a = test.a limit 1) ,(select NULL from test where tt.a = test.a limit 1)  from test tt;
+----------------------------------------+-------+-----------+---------------------------------------------------------------+
| id                                     | count | task      | operator info                                                 |
+----------------------------------------+-------+-----------+---------------------------------------------------------------+
| Projection_28                          | 1.00  | root      | Column#3, Column#7, Column#11, Column#15                      |
| └─Apply_30                             | 1.00  | root      | CARTESIAN left outer join, inner:Projection_65                |
|   ├─Apply_32                           | 1.00  | root      | CARTESIAN left outer join, inner:Projection_54                |
|   │ ├─Apply_34                         | 1.00  | root      | CARTESIAN left outer join, inner:Projection_43                |
|   │ │ ├─HashAgg_37                     | 1.00  | root      | funcs:sum(Column#28), firstrow(Column#29)                     |
|   │ │ │ └─Projection_76                | 1.00  | root      | cast(Column#1), Column#1                                      |
|   │ │ │   └─TableReader_42             | 1.00  | root      | data:TableScan_41                                             |
|   │ │ │     └─TableScan_41             | 1.00  | cop[tikv] | table:tt, range:[-inf,+inf], keep order:false, stats:pseudo   |
|   │ │ └─Projection_43                  | 0.00  | root      | NULL                                                          |
|   │ │   └─Limit_44                     | 0.00  | root      | offset:0, count:1                                             |
|   │ │     └─TableReader_50             | 0.00  | root      | data:Limit_49                                                 |
|   │ │       └─Limit_49                 | 0.00  | cop[tikv] | offset:0, count:1                                             |
|   │ │         └─Selection_48           | 0.00  | cop[tikv] | eq(Column#1, Column#5)                                        |
|   │ │           └─TableScan_47         | 1.00  | cop[tikv] | table:test, range:[-inf,+inf], keep order:false, stats:pseudo |
|   │ └─Projection_54                    | 0.00  | root      | NULL                                                          |
|   │   └─Limit_55                       | 0.00  | root      | offset:0, count:1                                             |
|   │     └─TableReader_61               | 0.00  | root      | data:Limit_60                                                 |
|   │       └─Limit_60                   | 0.00  | cop[tikv] | offset:0, count:1                                             |
|   │         └─Selection_59             | 0.00  | cop[tikv] | eq(Column#1, Column#9)                                        |
|   │           └─TableScan_58           | 1.00  | cop[tikv] | table:test, range:[-inf,+inf], keep order:false, stats:pseudo |
|   └─Projection_65                      | 0.00  | root      | NULL                                                          |
|     └─Limit_66                         | 0.00  | root      | offset:0, count:1                                             |
|       └─TableReader_72                 | 0.00  | root      | data:Limit_71                                                 |
|         └─Limit_71                     | 0.00  | cop[tikv] | offset:0, count:1                                             |
|           └─Selection_70               | 0.00  | cop[tikv] | eq(Column#1, Column#13)                                       |
|             └─TableScan_69             | 1.00  | cop[tikv] | table:test, range:[-inf,+inf], keep order:false, stats:pseudo |
+----------------------------------------+-------+-----------+---------------------------------------------------------------+
26 rows in set (0.00 sec)

mysql> select /*+ hash_agg() */ sum(a), (select NULL from test where tt.a = test.a limit 1),(select NULL from test where tt.a = test.a limit 1) ,(select NULL from test where tt.a = test.a limit 1)  from test tt; 

2. What did you expect to see?

The query returns result.

3. What did you see instead?

The query hangs forever.

4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?

build from master .

| Release Version: v4.0.0-alpha-535-g2f7a66f2d
Git Commit Hash: 2f7a66f2da241765c7a732c6b03b7ec363f861ac
Git Branch: master
UTC Build Time: 2019-10-16 08:54:36
GoVersion: go version go1.13 darwin/amd64
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false |