From 522e79f2e0dec684cca7db9958f1851d43387db3 Mon Sep 17 00:00:00 2001
From: Alexey Shekhirin <a.shekhirin@gmail.com>
Date: Mon, 29 Mar 2021 19:07:22 +0300
Subject: [PATCH] feat(search, criteria): introduce a percentage threshold to
 the asc/desc

---
 milli/src/search/criteria/asc_desc.rs | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/milli/src/search/criteria/asc_desc.rs b/milli/src/search/criteria/asc_desc.rs
index 6b8afad2c..d4b85b2bf 100644
--- a/milli/src/search/criteria/asc_desc.rs
+++ b/milli/src/search/criteria/asc_desc.rs
@@ -19,6 +19,10 @@ use crate::search::WordDerivationsCache;
 use crate::{FieldsIdsMap, FieldId, Index};
 use super::{Criterion, CriterionResult};
 
+/// If the number of candidates is lower or equal to the specified % of total number of documents,
+/// use simple sort. Otherwise, use facet database.
+const CANDIDATES_THRESHOLD: f64 = 0.1;
+
 pub struct AscDesc<'t> {
     index: &'t Index,
     rtxn: &'t heed::RoTxn<'t>,
@@ -237,7 +241,7 @@ fn field_id_facet_type(
 
 /// Returns an iterator over groups of the given candidates in ascending or descending order.
 ///
-/// It will either use an iterative or a recusrsive method on the whole facet database depending
+/// It will either use an iterative or a recursive method on the whole facet database depending
 /// on the number of candidates to rank.
 fn facet_ordered<'t>(
     index: &'t Index,
@@ -248,9 +252,11 @@ fn facet_ordered<'t>(
     candidates: RoaringBitmap,
 ) -> anyhow::Result<Box<dyn Iterator<Item = heed::Result<RoaringBitmap>> + 't>>
 {
+    let number_of_documents = index.number_of_documents(&rtxn)? as f64;
+
     match facet_type {
         FacetType::Float => {
-            if candidates.len() <= 1000 {
+            if candidates.len() / number_of_documents * 100 <= CANDIDATES_THRESHOLD {
                 let iter = iterative_facet_ordered_iter::<FieldDocIdFacetF64Codec, f64, OrderedFloat<f64>>(
                     index, rtxn, field_id, ascending, candidates,
                 )?;
@@ -266,7 +272,7 @@ fn facet_ordered<'t>(
             }
         },
         FacetType::Integer => {
-            if candidates.len() <= 1000 {
+            if candidates.len() / number_of_documents * 100 <= CANDIDATES_THRESHOLD {
                 let iter = iterative_facet_ordered_iter::<FieldDocIdFacetI64Codec, i64, i64>(
                     index, rtxn, field_id, ascending, candidates,
                 )?;