Optimization when posting list are saturated.

If a posting list doc freq is the segment reader's
max_doc, and if scoring does not matter, we can replace it
by a AllScorer.

In turn, in a boolean query, we can dismiss  all scorers and
empty scorers, to accelerate the request.

Author: fulmicoton-dd

src/aggregation/bucket/filter.rs

@@ -727,12 +727,13 @@ mod tests {
 
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut writer: IndexWriter = index.writer(50_000_000)?;
+        let mut writer: IndexWriter = index.writer_for_tests()?;
 
         writer.add_document(doc!(
             category => "electronics", brand => "apple",
             price => 999u64, rating => 4.5f64, in_stock => true
         ))?;
+        writer.commit()?;
         writer.add_document(doc!(
             category => "electronics", brand => "samsung",
             price => 799u64, rating => 4.2f64, in_stock => true
@@ -936,7 +937,7 @@ mod tests {
         let index = create_standard_test_index()?;
         let reader = index.reader()?;
         let searcher = reader.searcher();
-
+        assert_eq!(searcher.segment_readers().len(), 2);
         let agg = json!({
             "premium_electronics": {
                 "filter": "category:electronics AND price:[800 TO *]",

src/indexer/merger.rs

@@ -1518,7 +1518,9 @@ mod tests {
         let searcher = reader.searcher();
         let mut term_scorer = term_query
             .specialized_weight(EnableScoring::enabled_from_searcher(&searcher))?
-            .specialized_scorer(searcher.segment_reader(0u32), 1.0)?;
+            .specialized_scorer(searcher.segment_reader(0u32), 1.0)?
+            .into_term_scorer()
+            .unwrap();
         assert_eq!(term_scorer.doc(), 0);
         assert_nearly_equals!(term_scorer.block_max_score(), 0.0079681855);
         assert_nearly_equals!(term_scorer.score(), 0.0079681855);
@@ -1533,7 +1535,9 @@ mod tests {
         for segment_reader in searcher.segment_readers() {
             let mut term_scorer = term_query
                 .specialized_weight(EnableScoring::enabled_from_searcher(&searcher))?
-                .specialized_scorer(segment_reader, 1.0)?;
+                .specialized_scorer(segment_reader, 1.0)?
+                .into_term_scorer()
+                .unwrap();
             // the difference compared to before is intrinsic to the bm25 formula. no worries
             // there.
             for doc in segment_reader.doc_ids_alive() {
@@ -1558,7 +1562,9 @@ mod tests {
         let segment_reader = searcher.segment_reader(0u32);
         let mut term_scorer = term_query
             .specialized_weight(EnableScoring::enabled_from_searcher(&searcher))?
-            .specialized_scorer(segment_reader, 1.0)?;
+            .specialized_scorer(segment_reader, 1.0)?
+            .into_term_scorer()
+            .unwrap();
         // the difference compared to before is intrinsic to the bm25 formula. no worries there.
         for doc in segment_reader.doc_ids_alive() {
             assert_eq!(term_scorer.doc(), doc);

src/query/bm25.rs

@@ -1,3 +1,5 @@
+use std::sync::Arc;
+
 use crate::fieldnorm::FieldNormReader;
 use crate::query::Explanation;
 use crate::schema::Field;
@@ -57,31 +59,34 @@ fn cached_tf_component(fieldnorm: u32, average_fieldnorm: Score) -> Score {
     K1 * (1.0 - B + B * fieldnorm as Score / average_fieldnorm)
 }
 
-fn compute_tf_cache(average_fieldnorm: Score) -> [Score; 256] {
+fn compute_tf_cache(average_fieldnorm: Score) -> Arc<[Score; 256]> {
     let mut cache: [Score; 256] = [0.0; 256];
     for (fieldnorm_id, cache_mut) in cache.iter_mut().enumerate() {
         let fieldnorm = FieldNormReader::id_to_fieldnorm(fieldnorm_id as u8);
         *cache_mut = cached_tf_component(fieldnorm, average_fieldnorm);
     }
-    cache
+    Arc::new(cache)
 }
 
 /// A struct used for computing BM25 scores.
 #[derive(Clone)]
 pub struct Bm25Weight {
     idf_explain: Option<Explanation>,
     weight: Score,
-    cache: [Score; 256],
+    cache: Arc<[Score; 256]>,
     average_fieldnorm: Score,
 }
 
 impl Bm25Weight {
     /// Increase the weight by a multiplicative factor.
     pub fn boost_by(&self, boost: Score) -> Bm25Weight {
+        if boost == 1.0f32 {
+            return self.clone();
+        }
         Bm25Weight {
             idf_explain: self.idf_explain.clone(),
             weight: self.weight * boost,
-            cache: self.cache,
+            cache: self.cache.clone(),
             average_fieldnorm: self.average_fieldnorm,
         }
     }

src/query/boolean_query/boolean_weight.rs

@@ -9,7 +9,7 @@ use crate::query::score_combiner::{DoNothingCombiner, ScoreCombiner};
 use crate::query::term_query::TermScorer;
 use crate::query::weight::{for_each_docset_buffered, for_each_pruning_scorer, for_each_scorer};
 use crate::query::{
-    intersect_scorers, BufferedUnionScorer, EmptyScorer, Exclude, Explanation, Occur,
+    intersect_scorers, AllScorer, BufferedUnionScorer, EmptyScorer, Exclude, Explanation, Occur,
     RequiredOptionalScorer, Scorer, Weight,
 };
 use crate::{DocId, Score};
@@ -97,6 +97,15 @@ fn into_box_scorer<TScoreCombiner: ScoreCombiner>(
     }
 }
 
+enum ShouldScorersCombinationMethod {
+    // Should scorers are irrelevant.
+    Ignored,
+    // Only contributes to final score.
+    Optional(SpecializedScorer),
+    // Regardless of score, the should scorers may impact whether a document is matching or not.
+    Required(SpecializedScorer),
+}
+
 /// Weight associated to the `BoolQuery`.
 pub struct BooleanWeight<TScoreCombiner: ScoreCombiner> {
     weights: Vec<(Occur, Box<dyn Weight>)>,
@@ -159,90 +168,125 @@ impl<TScoreCombiner: ScoreCombiner> BooleanWeight<TScoreCombiner> {
     ) -> crate::Result<SpecializedScorer> {
         let num_docs = reader.num_docs();
         let mut per_occur_scorers = self.per_occur_scorers(reader, boost)?;
-        // Indicate how should clauses are combined with other clauses.
-        enum CombinationMethod {
-            Ignored,
-            // Only contributes to final score.
-            Optional(SpecializedScorer),
-            Required(SpecializedScorer),
+
+        // Indicate how should clauses are combined with must clauses.
+        let mut must_scorers: Vec<Box<dyn Scorer>> =
+            per_occur_scorers.remove(&Occur::Must).unwrap_or_default();
+        let must_special_scorer_counts = remove_and_count_all_and_empty_scorers(&mut must_scorers);
+
+        if must_special_scorer_counts.empty_count > 0 {
+            return Ok(SpecializedScorer::Other(Box::new(EmptyScorer)));
+        }
+
+        let mut should_scorers = per_occur_scorers.remove(&Occur::Should).unwrap_or_default();
+        let should_special_scorer_counts =
+            remove_and_count_all_and_empty_scorers(&mut should_scorers);
+
+        let mut exclude_scorers: Vec<Box<dyn Scorer>> = per_occur_scorers
+            .remove(&Occur::MustNot)
+            .unwrap_or_default();
+        let exclude_special_scorer_counts =
+            remove_and_count_all_and_empty_scorers(&mut exclude_scorers);
+
+        if exclude_special_scorer_counts.all_count > 0 {
+            // We exclude all documents at one point.
+            return Ok(SpecializedScorer::Other(Box::new(EmptyScorer)));
         }
-        let mut must_scorers = per_occur_scorers.remove(&Occur::Must);
-        let should_opt = if let Some(mut should_scorers) = per_occur_scorers.remove(&Occur::Should)
-        {
+
+        let minimum_number_should_match = self
+            .minimum_number_should_match
+            .saturating_sub(should_special_scorer_counts.all_count);
+
+        let should_scorers: ShouldScorersCombinationMethod = {
             let num_of_should_scorers = should_scorers.len();
-            if self.minimum_number_should_match > num_of_should_scorers {
+            if minimum_number_should_match > num_of_should_scorers {
+                // We don't have enough scorers to satisfy the minimum number of should matches.
+                // The request will match no documents.
                 return Ok(SpecializedScorer::Other(Box::new(EmptyScorer)));
             }
-            match self.minimum_number_should_match {
-                0 => CombinationMethod::Optional(scorer_union(
+            match minimum_number_should_match {
+                0 if num_of_should_scorers == 0 => ShouldScorersCombinationMethod::Ignored,
+                0 => ShouldScorersCombinationMethod::Optional(scorer_union(
                     should_scorers,
                     &score_combiner_fn,
                     num_docs,
                 )),
-                1 => CombinationMethod::Required(scorer_union(
+                1 => ShouldScorersCombinationMethod::Required(scorer_union(
                     should_scorers,
                     &score_combiner_fn,
                     num_docs,
                 )),
                 n if num_of_should_scorers == n => {
                     // When num_of_should_scorers equals the number of should clauses,
                     // they are no different from must clauses.
-                    must_scorers = match must_scorers.take() {
-                        Some(mut must_scorers) => {
-                            must_scorers.append(&mut should_scorers);
-                            Some(must_scorers)
-                        }
-                        None => Some(should_scorers),
-                    };
-                    CombinationMethod::Ignored
+                    must_scorers.append(&mut should_scorers);
+                    ShouldScorersCombinationMethod::Ignored
                 }
-                _ => CombinationMethod::Required(SpecializedScorer::Other(scorer_disjunction(
-                    should_scorers,
-                    score_combiner_fn(),
-                    self.minimum_number_should_match,
-                ))),
+                _ => ShouldScorersCombinationMethod::Required(SpecializedScorer::Other(
+                    scorer_disjunction(
+                        should_scorers,
+                        score_combiner_fn(),
+                        self.minimum_number_should_match,
+                    ),
+                )),
             }
+        };
+
+        let exclude_scorer_opt: Option<Box<dyn Scorer>> = if exclude_scorers.is_empty() {
+            None
         } else {
-            // None of should clauses are provided.
-            if self.minimum_number_should_match > 0 {
-                return Ok(SpecializedScorer::Other(Box::new(EmptyScorer)));
-            } else {
-                CombinationMethod::Ignored
-            }
+            let exclude_specialized_scorer: SpecializedScorer =
+                scorer_union(exclude_scorers, DoNothingCombiner::default, num_docs);
+            Some(into_box_scorer(
+                exclude_specialized_scorer,
+                DoNothingCombiner::default,
+                num_docs,
+            ))
         };
-        let exclude_scorer_opt: Option<Box<dyn Scorer>> = per_occur_scorers
-            .remove(&Occur::MustNot)
-            .map(|scorers| scorer_union(scorers, DoNothingCombiner::default, num_docs))
-            .map(|specialized_scorer: SpecializedScorer| {
-                into_box_scorer(specialized_scorer, DoNothingCombiner::default, num_docs)
-            });
-        let positive_scorer = match (should_opt, must_scorers) {
-            (CombinationMethod::Ignored, Some(must_scorers)) => {
-                SpecializedScorer::Other(intersect_scorers(must_scorers, num_docs))
+
+        let positive_scorer = match (should_scorers, must_scorers) {
+            (ShouldScorersCombinationMethod::Ignored, must_scorers) => {
+                let boxed_scorer: Box<dyn Scorer> = if must_scorers.is_empty() {
+                    if must_special_scorer_counts.all_count + should_special_scorer_counts.all_count
+                        > 0
+                    {
+                        Box::new(AllScorer::new(reader.max_doc()))
+                    } else {
+                        Box::new(EmptyScorer)
+                    }
+                } else {
+                    intersect_scorers(must_scorers, num_docs)
+                };
+                SpecializedScorer::Other(boxed_scorer)
             }
-            (CombinationMethod::Optional(should_scorer), Some(must_scorers)) => {
-                let must_scorer = intersect_scorers(must_scorers, num_docs);
-                if self.scoring_enabled {
-                    SpecializedScorer::Other(Box::new(
-                        RequiredOptionalScorer::<_, _, TScoreCombiner>::new(
+            (ShouldScorersCombinationMethod::Optional(should_scorer), must_scorers) => {
+                if must_scorers.is_empty() && must_special_scorer_counts.all_count == 0 {
+                    // Optional options are promoted to required if no must scorers exists.
+                    should_scorer
+                } else {
+                    let must_scorer = intersect_scorers(must_scorers, num_docs);
+                    if self.scoring_enabled {
+                        SpecializedScorer::Other(Box::new(RequiredOptionalScorer::<
+                            _,
+                            _,
+                            TScoreCombiner,
+                        >::new(
                             must_scorer,
                             into_box_scorer(should_scorer, &score_combiner_fn, num_docs),
-                        ),
-                    ))
-                } else {
-                    SpecializedScorer::Other(must_scorer)
+                        )))
+                    } else {
+                        SpecializedScorer::Other(must_scorer)
+                    }
                 }
             }
-            (CombinationMethod::Required(should_scorer), Some(mut must_scorers)) => {
-                must_scorers.push(into_box_scorer(should_scorer, &score_combiner_fn, num_docs));
-                SpecializedScorer::Other(intersect_scorers(must_scorers, num_docs))
-            }
-            (CombinationMethod::Ignored, None) => {
-                return Ok(SpecializedScorer::Other(Box::new(EmptyScorer)))
+            (ShouldScorersCombinationMethod::Required(should_scorer), mut must_scorers) => {
+                if must_scorers.is_empty() {
+                    should_scorer
+                } else {
+                    must_scorers.push(into_box_scorer(should_scorer, &score_combiner_fn, num_docs));
+                    SpecializedScorer::Other(intersect_scorers(must_scorers, num_docs))
+                }
             }
-            (CombinationMethod::Required(should_scorer), None) => should_scorer,
-            // Optional options are promoted to required if no must scorers exists.
-            (CombinationMethod::Optional(should_scorer), None) => should_scorer,
         };
         if let Some(exclude_scorer) = exclude_scorer_opt {
             let positive_scorer_boxed =
@@ -257,6 +301,30 @@ impl<TScoreCombiner: ScoreCombiner> BooleanWeight<TScoreCombiner> {
     }
 }
 
+#[derive(Default, Copy, Clone, Debug)]
+struct AllAndEmptyScorerCounts {
+    all_count: usize,
+    empty_count: usize,
+}
+
+fn remove_and_count_all_and_empty_scorers(
+    scorers: &mut Vec<Box<dyn Scorer>>,
+) -> AllAndEmptyScorerCounts {
+    let mut counts = AllAndEmptyScorerCounts::default();
+    scorers.retain(|scorer| {
+        if scorer.is::<AllScorer>() {
+            counts.all_count += 1;
+            false
+        } else if scorer.is::<EmptyScorer>() {
+            counts.empty_count += 1;
+            false
+        } else {
+            true
+        }
+    });
+    counts
+}
+
 impl<TScoreCombiner: ScoreCombiner + Sync> Weight for BooleanWeight<TScoreCombiner> {
     fn scorer(&self, reader: &SegmentReader, boost: Score) -> crate::Result<Box<dyn Scorer>> {
         let num_docs = reader.num_docs();