neilconway opened a new pull request, #21154:
URL: https://github.com/apache/datafusion/pull/21154
## Which issue does this PR close?
- Closes #17789.
## Rationale for this change
`string_agg` previously didn't support `GroupsAccumulator`; adding support
for it can significantly improve performance, particularly when there are many
groups.
Benchmarks (M4 Max):
- string_agg_query_group_by_few_groups (~10): 645 µs → 564 µs, -11%
- string_agg_query_group_by_mid_groups (~1,000): 2,692 µs → 871 µs, -68%
- string_agg_query_group_by_many_groups (~65,000): 16,606 µs → 1,147 µs,
-93%
## What changes are included in this PR?
* Add end-to-end benchmark for `string_agg`
* Implement `GroupsAccumulator` API for `string_agg`
* Add unit tests
* Minor code cleanup for existing `string_agg` code paths
## Are these changes tested?
Yes.
## Are there any user-facing changes?
No, other than a change to an error message string.
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