nuno-faria opened a new pull request, #17528:
URL: https://github.com/apache/datafusion/pull/17528
## Which issue does this PR close?
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- N/A.
## Rationale for this change
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Why are you proposing this change? If this is already explained clearly in
the issue then this section is not needed.
Explaining clearly why changes are proposed helps reviewers understand your
changes and offer better suggestions for fixes.
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Improves the performance of window functions in more than 3x when there are
a large number of distinct partition keys. The performance with few groups
remains the same.
I believe the performance could be further improved, but it might require
deeper changes.
Here is a small benchmark:
```rust
use datafusion::error::Result;
use datafusion::prelude::SessionContext;
use tokio::time::Instant;
#[tokio::main]
async fn main() -> Result<()> {
let ctx = SessionContext::new();
ctx.sql("SET datafusion.execution.target_partitions = '1';")
.await?
.collect()
.await?;
ctx.sql("create table t (k1 int, k2 int, v int);")
.await?
.collect()
.await?;
ctx.sql("insert into t select i as k1, 1 as k2, i as v from
generate_series(1, 10000000) t(i);")
.await?
.collect()
.await?;
// partition by k1: each key is unique
let t = Instant::now();
ctx.sql("
explain analyze
select *, rank() over(partition by k1 order by v) as rank
from t
"
)
.await?
.collect()
.await?;
println!("partition by k1: {}s", t.elapsed().as_secs_f64());
// partition by k2: each key is the same
let t = Instant::now();
ctx.sql("
explain analyze
select *, rank() over(partition by k2 order by v) as rank
from t
"
)
.await?
.collect()
.await?;
println!("partition by k2: {}s", t.elapsed().as_secs_f64());
Ok(())
}
```
```
# before
partition by k1: 62.201990669s
partition by k2: 1.89616558s
# after
partition by k1: 18.177335377s
partition by k2: 1.870575527s
```
## What changes are included in this PR?
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There is no need to duplicate the description in the issue here but it is
sometimes worth providing a summary of the individual changes in this PR.
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- Reuse `WindowAggState` to avoid potentially having to create many in
`StandardWindowExpr::evaluate_stateful` (`standard.rs`).
- Avoid `concat` in `WindowAggState::update` when the existing result in
empty (`window_state.rs`).
- Use `to_array` instead of `iter_to_array` when an `ArrayRef` only has a
single row, in `StandardWindowExpr::evaluate_stateful` (`standard.rs`).
- Concat all batches once instead of one at a time, in
`get_aggregate_result_out_column` (`bounded_window_agg_exec.rs`).
- Use `clone` instead of `slice` when the entire column is used, in
`get_aggregate_result_out_column` (`bounded_window_agg_exec.rs`).
- Avoid concatenating batches unnecessarily in
`PartitionSearcher::update_partition_batch` (`bounded_window_agg_exec.rs`).
- Iterate over `IndexMap` and probe `HashMap` instead of the other way
around, in `SortedSearch::calculate_n_out_row` (`bounded_window_agg_exec.rs`).
## Are these changes tested?
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1. Prevent the code from being accidentally broken by subsequent changes
2. Serve as another way to document the expected behavior of the code
If tests are not included in your PR, please explain why (for example, are
they covered by existing tests)?
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Yes.
## Are there any user-facing changes?
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updated before approving the PR.
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If there are any breaking changes to public APIs, please add the `api
change` label.
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No.
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