[HIVE-23954] count(*) with count(distinct) gives wrong results with hive.optimize.countdistinct=true

• Type: Bug
• Status: Patch Available
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 3.1.0, 3.0.0
• Component/s: Logical Optimizer
• Labels: pull-request-available
• Assignee: Eugene Chung
• Reporter: Eugene Chung
• Created: 30/Jul/20 05:29
• Updated: 25/Oct/20 01:01

Description

select count(*), count(distinct mid) from db1.table1 where partitioned_column = '...'

 

is not working properly when hive.optimize.countdistinct is true. By default, it's true for all 3.x versions.

In the two plans below, the aggregations part in the Output of Group By Operator of Map 1 are different.

 

- hive.optimize.countdistinct=false

+----------------------------------------------------+
|                      Explain                       |
+----------------------------------------------------+
| Plan optimized by CBO.                             |
|                                                    |
| Vertex dependency in root stage                    |
| Reducer 2 <- Map 1 (SIMPLE_EDGE)                   |
|                                                    |
| Stage-0                                            |
|   Fetch Operator                                   |
|     limit:-1                                       |
|     Stage-1                                        |
|       Reducer 2                                    |
|       File Output Operator [FS_7]                  |
|         Group By Operator [GBY_5] (rows=1 width=24) |
|           Output:["_col0","_col1"],aggregations:["count(VALUE._col0)","count(DISTINCT KEY._col0:0._col0)"] |
|         <-Map 1 [SIMPLE_EDGE]                      |
|           SHUFFLE [RS_4]                           |
|             Group By Operator [GBY_3] (rows=343640771 width=4160) |
|               Output:["_col0","_col1","_col2"],aggregations:["count()","count(DISTINCT mid)"],keys:mid |
|               Select Operator [SEL_2] (rows=343640771 width=4160) |
|                 Output:["mid"]                     |
|                 TableScan [TS_0] (rows=343640771 width=4160) |
|                   db1@table1,table1,Tbl:COMPLETE,Col:NONE,Output:["mid"] |
|                                                    |
+----------------------------------------------------+

 

- hive.optimize.countdistinct=true

+----------------------------------------------------+
|                      Explain                       |
+----------------------------------------------------+
| Plan optimized by CBO.                             |
|                                                    |
| Vertex dependency in root stage                    |
| Reducer 2 <- Map 1 (SIMPLE_EDGE)                   |
|                                                    |
| Stage-0                                            |
|   Fetch Operator                                   |
|     limit:-1                                       |
|     Stage-1                                        |
|       Reducer 2                                    |
|       File Output Operator [FS_7]                  |
|         Group By Operator [GBY_14] (rows=1 width=16) |
|           Output:["_col0","_col1"],aggregations:["count(_col1)","count(_col0)"] |
|           Group By Operator [GBY_11] (rows=343640771 width=4160) |
|             Output:["_col0","_col1"],aggregations:["count(VALUE._col0)"],keys:KEY._col0 |
|           <-Map 1 [SIMPLE_EDGE]                    |
|             SHUFFLE [RS_10]                        |
|               PartitionCols:_col0                  |
|               Group By Operator [GBY_9] (rows=343640771 width=4160) |
|                 Output:["_col0","_col1"],aggregations:["count()"],keys:mid |
|                 Select Operator [SEL_2] (rows=343640771 width=4160) |
|                   Output:["mid"]                   |
|                   TableScan [TS_0] (rows=343640771 width=4160) |
|                     db1@table1,table1,Tbl:COMPLETE,Col:NONE,Output:["mid"] |
|                                                    |
+----------------------------------------------------+

Issue Links

• is caused by: HIVE-16654 Optimize a combination of avg(), sum(), count(distinct) etc
• links to: GitHub Pull Request #1414