alamb commented on issue #7460:
URL: https://github.com/apache/arrow-rs/issues/7460#issuecomment-2843142141
I did some analysis on `hits.parquet`:
* Selectivity is: `13172392` / `99997497` = `0.132`
* Average run length of each `RowSelection`: `99997497` / `14054784` =
`7.114`
<details><summary>Worked Details</summary>
<p>
```sql
> SELECT count("SearchPhrase") FROM hits_partitioned;
+--------------------------------------+
| count(hits_partitioned.SearchPhrase) |
+--------------------------------------+
| 99997497 |
+--------------------------------------+
> SELECT count("SearchPhrase") FROM hits_partitioned WHERE "SearchPhrase" <>
'';
+--------------------------------------+
| count(hits_partitioned.SearchPhrase) |
+--------------------------------------+
| 13172392 |
+--------------------------------------+
```
So selectivity is: 13172392 / 99997497 = 0.1317272171
To figure out the pattern of passing rows, we want to know how many
contiguous rows there are in the matched filter
```
(t)
(t)
(t)
(f)
(f)
```
Would have two selections (3 true, 2 false)
Here is the sql:
```sql
SET datafusion.execution.target_partitions = 1;
WITH
hits as (
SELECT
"SearchPhrase",
row_number() OVER () as rn
FROM
'hits.parquet'
)
,results as (
SELECT
rn,
"SearchPhrase",
"SearchPhrase" <> '',
("SearchPhrase" <> '') = (LAG("SearchPhrase" <> '', 1) OVER ()) as
"filter_same_as_previous"
FROM
hits
)
SELECT
filter_same_as_previous, COUNT(*)
FROM results
GROUP BY
filter_same_as_previous
--LIMIT 10
;
+-------------------------+----------+
| filter_same_as_previous | count(*) |
+-------------------------+----------+
| NULL | 1 |
| true | 85942712 |
| false | 14054784 |
+-------------------------+----------+
```
</p>
</details>
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