wudidapaopao commented on code in PR #25536:
URL: https://github.com/apache/datafusion/pull/25536#discussion_r4065514376
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datafusion/expr/src/udaf.rs:
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@@ -311,6 +312,17 @@ impl AggregateUDF {
self.inner.simplify()
}
+ /// Returns this aggregate function's candidate decomposition, if any.
+ ///
+ /// See [`AggregateUDFImpl::decompose`] for more details.
+ pub fn decompose(
Review Comment:
Thanks, I considered using `simplify`. I think we should retain the AVG
accumulator and only decompose `AVG` when its generated `SUM` or `COUNT` can be
shared. If implemented in `simplify`, every AVG would be unconditionally
rewritten into `SUM/COUNT`.
Benchmark: 20 million random non-null `Int64` rows, single-threaded.
| Scenario | SQL | Before decomposition | After decomposition | Change |
|---|---|---:|---:|---:|
| No sharing | `SELECT AVG(x) FROM t` | 9.06 ms | 10.72 ms | 18.29% slower |
| One reusable SUM | `SELECT SUM(CAST(x AS DOUBLE)), AVG(x) FROM t` | 11.72
ms | 10.79 ms | 7.95% faster |
| Three reusable SUMs | `SELECT SUM(CAST(x AS DOUBLE)), AVG(x), SUM(CAST(y
AS DOUBLE)), AVG(y), SUM(CAST(z AS DOUBLE)), AVG(z) FROM t` | 32.91 ms | 27.85
ms | 15.38% faster |
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