[IMPALA-9959] Implement ds_kll_sketch() and ds_kll_quantile() functions

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: Impala 4.0.0
• Component/s: Backend, Frontend
• Epic Link: unlabelled-IMPALA-9594
• Epic Color: ghx-label-8
• Assignee: Gabor Kaszab
• Reporter: Gabor Kaszab
• Created: 15/Jul/20 15:44
• Updated: 25/Aug/20 21:41
• Resolved: 03/Aug/20 06:52

Description

1:
STRING ds_kll_sketch(float)
Accepts float as parameter and returns a DataSketches KLL sketch in string type (or binary once that work is submitted).

2:
FLOAT (or DOUBLE?) ds_kll_quantile(KLL sketch, double)
Accepts two parameters: a KLL sketch created by ds_hll_sketch() and a double in [0, 1] to represent the quantile.
At this point I'm not sure about the return value, it's either a float or double, it's a subject of further investigation.

Example:

select ds_kll_quantile(ds_kll_sketch(cast(int_col as float)), 1) from table_name;
+------+
| _c0  |
+------+
| 1.0  |
+------+

Some further examples found here:
https://datasketches.apache.org/docs/Quantiles/QuantilesCppExample.html