sandeshkr419 commented on code in PR #23816:
URL: https://github.com/apache/datafusion/pull/23816#discussion_r3677571483
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datafusion/functions-aggregate/src/approx_distinct.rs:
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@@ -654,12 +701,29 @@ impl Default for ApproxDistinct {
#[derive(PartialEq, Eq, Hash)]
pub struct ApproxDistinct {
signature: Signature,
+ /// HLL register precision. Only used for types that take the HLL code path
+ /// (i.e. not Boolean / small-int types, which use exact bitmap counting).
+ hll_precision: usize,
}
impl ApproxDistinct {
pub fn new() -> Self {
+ Self::with_hll_precision(DEFAULT_HLL_P)
+ }
+
+ /// Creates an `ApproxDistinct` that uses HLL sketches with `2^p`
registers.
+ ///
+ /// This only has effect for types that use the HLL accumulator path. Small
+ /// integer and boolean types use exact bitmap counting regardless of this
+ /// value. Valid range: `HLL_P_MIN..=HLL_P_MAX` (4..=18).
+ pub fn with_hll_precision(p: usize) -> Self {
Review Comment:
Good call, replaced the `assert!` with `plan_err!` so invalid precision
surfaces as a clean DataFusion error rather than a panic.
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