[IMPALA-6295] Inconsistent handling of 'nan' and 'inf' with min/max analytic fns

• Type: Bug
• Status: Resolved
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: Impala 2.11.0
• Fix Version/s: Impala 2.12.0
• Component/s: Backend
• Labels: codegen correctness
• Epic Color: ghx-label-1
• Assignee: Thomas Tauber-Marshall
• Reporter: Thomas Tauber-Marshall
• Created: 07/Dec/17 23:52
• Updated: 04/Jan/18 18:01
• Resolved: 04/Jan/18 18:01

Description

Incorrect results are returned in some cases where 'nan'/'inf' are the only values in the group and codegen is enabled:

> set DISABLE_CODEGEN_ROWS_THRESHOLD set to 0

> select * from test1 order by col1
+------+-----------+
| col0 | col1      |
+------+-----------+
| 0    | NaN       |
| 2    | -Infinity |
| 3    | 0         |
| 1    | Infinity  |
+------+-----------+

> set DISABLE_CODEGEN set to true
> select col0, min(col1) from test1 group by col0 order by col0
+------+-----------+
| col0 | min(col1) |
+------+-----------+
| 0    | NaN       |
| 1    | Infinity  |
| 2    | -Infinity |
| 3    | 0         |
+------+-----------+

> set DISABLE_CODEGEN set to false
> select col0, min(col1) from test1 group by col0 order by col0
+------+------------------------+
| col0 | min(col1)              |
+------+------------------------+
| 0    | 1.797693134862316e+308 |
| 1    | 1.797693134862316e+308 |
| 2    | -Infinity              |
| 3    | 0                      |
+------+------------------------+

> set DISABLE_CODEGEN set to true
> select col0, max(col1) from test1 group by col0 order by col0
+------+-----------+
| col0 | max(col1) |
+------+-----------+
| 0    | NaN       |
| 1    | Infinity  |
| 2    | -Infinity |
| 3    | 0         |
+------+-----------+

> set DISABLE_CODEGEN set to false
> select col0, max(col1) from test1 group by col0 order by col0
+------+-------------------------+
| col0 | max(col1)               |
+------+-------------------------+
| 0    | -1.797693134862316e+308 |
| 1    | Infinity                |
| 2    | -1.797693134862316e+308 |
| 3    | 0                       |
+------+-------------------------+

We also appear to never return 'nan' as a min or max value despite sorted it as the lowest value when ordering a table (perhaps this is the intended behavior?):

> set DISABLE_CODEGEN_ROWS_THRESHOLD set to 0
> select * from test2 order by col1
+------+-----------+
| col0 | col1      |
+------+-----------+
| 0    | NaN       |
| 2    | -Infinity |
| 0    | 0         |
| 3    | 0         |
| 1    | 1         |
| 2    | 2         |
| 3    | 3         |
| 1    | Infinity  |
+------+-----------+

> set DISABLE_CODEGEN set to true
> select col0, min(col1) from test2 group by col0 order by col0
+------+-----------+
| col0 | min(col1) |
+------+-----------+
| 0    | 0         |
| 1    | 1         |
| 2    | -Infinity |
| 3    | 0         |
+------+-----------+

> set DISABLE_CODEGEN set to false
> select col0, min(col1) from test2 group by col0 order by col0
+------+-----------+
| col0 | min(col1) |
+------+-----------+
| 0    | 0         |
| 1    | 1         |
| 2    | -Infinity |
| 3    | 0         |
+------+-----------+

> set DISABLE_CODEGEN set to true
> select col0, max(col1) from test2 group by col0 order by col0
+------+-----------+
| col0 | max(col1) |
+------+-----------+
| 0    | 0         |
| 1    | Infinity  |
| 2    | 2         |
| 3    | 3         |
+------+-----------+

> set DISABLE_CODEGEN set to false
> select col0, max(col1) from test2 group by col0 order by col0
+------+-----------+
| col0 | max(col1) |
+------+-----------+
| 0    | 0         |
| 1    | Infinity  |
| 2    | 2         |
| 3    | 3         |
+------+-----------+

Changing LlvmCodeGen::CodegenMinMax to use OLT/OGT float comparison functions appears to solve the first case (at least for 'nan'), but leads to us returning 'nan' as a max value in the second case.