mustafasrepo opened a new pull request, #4989:
URL: https://github.com/apache/arrow-datafusion/pull/4989
# Which issue does this PR close?
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Closes #4979
# Rationale for this change
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During range calculation for window frames, we can use linear search instead
of bisect. Since we know that table is already sorted and we would progress
only in one direction. Linear search is amortized constant (When window frame
boundaries are static). Hence this version is more optimal than current bisect
implementation (where search complexity is log(n)). This change decreases
overall window range calculation complexity from `O(n*log(n))` to `O(n)`.
# What changes are included in this PR?
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# Are these changes tested?
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Existing tests verify window range calculation correctness. Unit tests for
`linear_search` is also added. We also compared time elapsed during Window
result calculation for the query
```sql
SELECT SUM(a) OVER(ORDER BY a RANGE BETWEEN 10 PRECEDING AND 10 FOLLOWING)
FROM t1;
```
. Time comparison between linear and bisect version for different conditions
can be seen in table below.
n_row | distinct | linear(mean) | linear(median) | bisect(mean) |
bisect(median)
-- | -- | -- | -- | -- | --
100 | 10 | 1.199524ms | 772.125µs | 2.065253ms | 1.501125ms
100 | 100_000_000 | 1.614941ms | 1.599208ms | 2.30337ms | 2.346416ms
1000 | 10 | 4.521795ms | 4.417125ms | 10.986941ms | 10.994333ms
1000 | 100_000_000 | 11.82327ms | 11.8265ms | 23.83402ms | 23.641541ms
100_000 | 10 | 428.01742ms | 428.022791ms | 1.661792712s | 1.666531666s
100_000 | 100_000_000 | 1.190898003s | 1.18136925s | 3.446534628s |
3.446675916s
# Are there any user-facing changes?
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No.
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