Implement attribute criterion

* Implement WordLevelIterator
* Implement QueryLevelIterator
* Implement set algorithm based on iterators

Not tested + Some TODO to fix

milli/src/search/criteria/attribute.rs

@@ -1,17 +1,17 @@
-use std::cmp;
+use std::{cmp::{self, Ordering}, collections::BinaryHeap};
 use std::collections::{BTreeMap, HashMap, btree_map};
 use std::mem::take;
 
 use roaring::RoaringBitmap;
 
-use crate::{search::build_dfa};
+use crate::{TreeLevel, search::build_dfa};
 use crate::search::criteria::Query;
 use crate::search::query_tree::{Operation, QueryKind};
 use crate::search::WordDerivationsCache;
 use super::{Criterion, CriterionResult, Context, resolve_query_tree};
 
 pub struct Attribute<'t> {
-    ctx: &'t dyn Context,
+    ctx: &'t dyn Context<'t>,
     query_tree: Option<Operation>,
     candidates: Option<RoaringBitmap>,
     bucket_candidates: RoaringBitmap,
@@ -21,7 +21,7 @@ pub struct Attribute<'t> {
 }
 
 impl<'t> Attribute<'t> {
-    pub fn new(ctx: &'t dyn Context, parent: Box<dyn Criterion + 't>) -> Self {
+    pub fn new(ctx: &'t dyn Context<'t>, parent: Box<dyn Criterion + 't>) -> Self {
         Attribute {
             ctx,
             query_tree: None,
@@ -51,23 +51,27 @@ impl<'t> Criterion for Attribute<'t> {
                         flatten_query_tree(&qt)
                     });
 
-                    let current_buckets = match self.current_buckets.as_mut() {
-                        Some(current_buckets) => current_buckets,
-                        None => {
-                            let new_buckets = linear_compute_candidates(self.ctx, flattened_query_tree, candidates)?;
-                            self.current_buckets.get_or_insert(new_buckets.into_iter())
-                        },
-                    };
+                    let found_candidates = if candidates.len() < 1000 {
+                        let current_buckets = match self.current_buckets.as_mut() {
+                            Some(current_buckets) => current_buckets,
+                            None => {
+                                let new_buckets = linear_compute_candidates(self.ctx, flattened_query_tree, candidates)?;
+                                self.current_buckets.get_or_insert(new_buckets.into_iter())
+                            },
+                        };
 
-                    let found_candidates = match current_buckets.next() {
-                        Some((_score, candidates)) => candidates,
-                        None => {
-                            return Ok(Some(CriterionResult {
-                                query_tree: self.query_tree.take(),
-                                candidates: self.candidates.take(),
-                                bucket_candidates: take(&mut self.bucket_candidates),
-                            }));
-                        },
+                        match current_buckets.next() {
+                            Some((_score, candidates)) => candidates,
+                            None => {
+                                return Ok(Some(CriterionResult {
+                                    query_tree: self.query_tree.take(),
+                                    candidates: self.candidates.take(),
+                                    bucket_candidates: take(&mut self.bucket_candidates),
+                                }));
+                            },
+                        }
+                    } else {
+                        set_compute_candidates(self.ctx, flattened_query_tree, candidates)?
                     };
 
                     candidates.difference_with(&found_candidates);
@@ -114,6 +118,316 @@ impl<'t> Criterion for Attribute<'t> {
     }
 }
 
+struct WordLevelIterator<'t, 'q> {
+    inner: Box<dyn Iterator<Item =heed::Result<((&'t str, TreeLevel, u32, u32), RoaringBitmap)>> + 't>,
+    level: TreeLevel,
+    interval_size: u32,
+    word: &'q str,
+    in_prefix_cache: bool,
+    inner_next: Option<(u32, u32, RoaringBitmap)>,
+    current_interval: Option<(u32, u32)>,
+}
+
+impl<'t, 'q> WordLevelIterator<'t, 'q> {
+    fn new(ctx: &'t dyn Context<'t>, query: &'q Query) -> heed::Result<Option<Self>> {
+        // TODO make it typo/prefix tolerant
+        let word = query.kind.word();
+        let in_prefix_cache = query.prefix && ctx.in_prefix_cache(word);
+        match ctx.word_position_last_level(word, in_prefix_cache)? {
+            Some(level) =>  {
+                let interval_size = 4u32.pow(Into::<u8>::into(level.clone()) as u32);
+                let inner = ctx.word_position_iterator(word, level, in_prefix_cache, None, None)?;
+                Ok(Some(Self { inner, level, interval_size, word, in_prefix_cache, inner_next: None, current_interval: None }))
+            },
+            None => Ok(None),
+        }
+    }
+
+    fn dig(&self, ctx: &'t dyn Context<'t>, level: &TreeLevel) -> heed::Result<Self> {
+        let level = level.min(&self.level).clone();
+        let interval_size = 4u32.pow(Into::<u8>::into(level.clone()) as u32);
+        let word = self.word;
+        let in_prefix_cache = self.in_prefix_cache;
+        // TODO try to dig starting from the current interval
+        // let left = self.current_interval.map(|(left, _)| left);
+        let inner = ctx.word_position_iterator(word, level, in_prefix_cache, None, None)?;
+
+        Ok(Self {inner, level, interval_size, word, in_prefix_cache, inner_next: None, current_interval: None})
+    }
+
+    fn next(&mut self) -> heed::Result<Option<(u32, u32, RoaringBitmap)>> {
+        fn is_next_interval(last_right: u32, next_left: u32) -> bool { last_right + 1 == next_left }
+
+        let inner_next = match self.inner_next.take() {
+            Some(inner_next) => Some(inner_next),
+            None => self.inner.next().transpose()?.map(|((_, _, left, right), docids)| (left, right, docids)),
+        };
+
+        match inner_next {
+            Some((left, right, docids)) => {
+                match self.current_interval {
+                    Some((last_left, last_right)) if !is_next_interval(last_right, left) => {
+                        let blank_left = last_left + self.interval_size;
+                        let blank_right = last_right + self.interval_size;
+                        self.current_interval = Some((blank_left, blank_right));
+                        self.inner_next = Some((left, right, docids));
+                        Ok(Some((blank_left, blank_right, RoaringBitmap::new())))
+                    },
+                    _ => {
+                        self.current_interval = Some((left, right));
+                        Ok(Some((left, right, docids)))
+                    }
+                }
+            },
+            None => Ok(None),
+        }
+    }
+}
+
+struct QueryLevelIterator<'t, 'q> {
+    previous: Option<Box<QueryLevelIterator<'t, 'q>>>,
+    inner: Vec<WordLevelIterator<'t, 'q>>,
+    level: TreeLevel,
+    accumulator: Vec<Option<(u32, u32, RoaringBitmap)>>,
+    previous_accumulator: Vec<Option<(u32, u32, RoaringBitmap)>>,
+}
+
+impl<'t, 'q> QueryLevelIterator<'t, 'q> {
+    fn new(ctx: &'t dyn Context<'t>, queries: &'q Vec<Query>) -> heed::Result<Option<Self>> {
+        let mut inner = Vec::with_capacity(queries.len());
+        for query in queries {
+            if let Some(word_level_iterator) = WordLevelIterator::new(ctx, query)? {
+                inner.push(word_level_iterator);
+            }
+        }
+
+        let highest = inner.iter().max_by_key(|wli| wli.level).map(|wli| wli.level.clone());
+        match highest {
+            Some(level) => Ok(Some(Self {
+                previous: None,
+                inner,
+                level,
+                accumulator: vec![],
+                previous_accumulator: vec![],
+            })),
+            None => Ok(None),
+        }
+    }
+
+    fn previous(&mut self, previous: QueryLevelIterator<'t, 'q>) -> &Self {
+        self.previous = Some(Box::new(previous));
+        self
+    }
+
+    fn dig(&self, ctx: &'t dyn Context<'t>) -> heed::Result<Self> {
+        let (level, previous) = match &self.previous {
+            Some(previous) => {
+                let previous = previous.dig(ctx)?;
+                (previous.level.min(self.level), Some(Box::new(previous)))
+            },
+            None => (self.level.saturating_sub(1), None),
+        };
+
+        let mut inner = Vec::with_capacity(self.inner.len());
+        for word_level_iterator in self.inner.iter() {
+            inner.push(word_level_iterator.dig(ctx, &level)?);
+        }
+
+        Ok(Self {previous, inner, level, accumulator: vec![], previous_accumulator: vec![]})
+    }
+
+
+
+    fn inner_next(&mut self, level: TreeLevel) -> heed::Result<Option<(u32, u32, RoaringBitmap)>> {
+        let mut accumulated: Option<(u32, u32, RoaringBitmap)> = None;
+        let u8_level = Into::<u8>::into(level);
+        let interval_size = 4u32.pow(u8_level as u32);
+        for wli in self.inner.iter_mut() {
+            let wli_u8_level = Into::<u8>::into(wli.level.clone());
+            let accumulated_count = 4u32.pow((u8_level - wli_u8_level) as u32);
+            for _ in 0..accumulated_count {
+                if let Some((next_left, _, next_docids)) =  wli.next()? {
+                    accumulated = accumulated.take().map(
+                        |(acc_left, acc_right, mut acc_docids)| {
+                            acc_docids.union_with(&next_docids);
+                            (acc_left, acc_right, acc_docids)
+                        }
+                    ).or_else(|| Some((next_left, next_left + interval_size, next_docids)));
+                }
+            }
+        }
+
+        Ok(accumulated)
+    }
+
+    fn next(&mut self) -> heed::Result<(TreeLevel, Option<(u32, u32, RoaringBitmap)>)> {
+        let previous_result = match self.previous.as_mut() {
+            Some(previous) => {
+                Some(previous.next()?)
+            },
+            None => None,
+        };
+
+        match previous_result {
+            Some((previous_level, previous_next)) => {
+                let inner_next = self.inner_next(previous_level)?;
+                self.accumulator.push(inner_next);
+                self.previous_accumulator.push(previous_next);
+                // TODO @many clean firsts intervals of both accumulators when both RoaringBitmap are empty,
+                // WARNING the cleaned intervals count needs to be kept to skip at the end
+                let mut merged_interval = None;
+                for current in self.accumulator.iter().rev().zip(self.previous_accumulator.iter()) {
+                    if let (Some((left_a, right_a, a)), Some((left_b, right_b, b))) = current {
+                        let (_, _, merged_docids) = merged_interval.get_or_insert_with(|| (left_a + left_b, right_a + right_b, RoaringBitmap::new()));
+                        merged_docids.union_with(&(a & b));
+                    }
+                }
+                Ok((previous_level, merged_interval))
+            },
+            None => {
+                let level = self.level.clone();
+                let next_interval = self.inner_next(level.clone())?;
+                self.accumulator = vec![next_interval.clone()];
+                Ok((level, next_interval))
+            }
+        }
+    }
+}
+
+struct Branch<'t, 'q> {
+    query_level_iterator: QueryLevelIterator<'t, 'q>,
+    last_result: Option<(u32, u32, RoaringBitmap)>,
+    tree_level: TreeLevel,
+    branch_size: u32,
+}
+
+impl<'t, 'q> Branch<'t, 'q> {
+    fn cmp(&self, other: &Self) -> Ordering {
+        fn compute_rank(left: u32, branch_size: u32) -> u32 { left.saturating_sub((1..branch_size).sum()) / branch_size }
+        match (&self.last_result, &other.last_result) {
+            (Some((s_left, _, _)), Some((o_left, _, _))) => {
+                // we compute a rank form the left interval.
+                let self_rank = compute_rank(*s_left, self.branch_size);
+                let other_rank = compute_rank(*o_left, other.branch_size);
+                let left_cmp = self_rank.cmp(&other_rank).reverse();
+                // on level: higher is better,
+                // we want to reduce highest levels first.
+                let level_cmp = self.tree_level.cmp(&other.tree_level);
+
+                left_cmp.then(level_cmp)
+            },
+            (Some(_), None) => Ordering::Greater,
+            (None, Some(_)) => Ordering::Less,
+            (None, None) => Ordering::Equal,
+        }
+    }
+}
+
+impl<'t, 'q> Ord for Branch<'t, 'q> {
+    fn cmp(&self, other: &Self) -> Ordering {
+        self.cmp(other)
+    }
+}
+
+impl<'t, 'q> PartialOrd for Branch<'t, 'q> {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl<'t, 'q> PartialEq for Branch<'t, 'q> {
+    fn eq(&self, other: &Self) -> bool {
+        self.cmp(other) == Ordering::Equal
+    }
+}
+
+impl<'t, 'q> Eq for Branch<'t, 'q> {}
+
+fn initialize_query_level_iterators<'t, 'q>(
+    ctx: &'t dyn Context<'t>,
+    branches: &'q Vec<Vec<Vec<Query>>>,
+) -> heed::Result<BinaryHeap<Branch<'t, 'q>>> {
+
+    let mut positions = BinaryHeap::with_capacity(branches.len());
+    for branch in branches {
+        let mut branch_positions = Vec::with_capacity(branch.len());
+        for query in  branch {
+            match QueryLevelIterator::new(ctx, query)? {
+                Some(qli) => branch_positions.push(qli),
+                None => {
+                    // the branch seems to be invalid, so we skip it.
+                    branch_positions.clear();
+                    break;
+                },
+            }
+        }
+        // QueryLevelIterator need to be sorted by level and folded in descending order.
+        branch_positions.sort_unstable_by_key(|qli| qli.level);
+        let folded_query_level_iterators =  branch_positions
+            .into_iter()
+            .rev()
+            .fold(None, |fold: Option<QueryLevelIterator>, qli| match fold {
+                Some(mut fold) => {
+                    fold.previous(qli);
+                    Some(fold)
+                },
+                None => Some(qli),
+        });
+
+        if let Some(mut folded_query_level_iterators) = folded_query_level_iterators {
+            let (tree_level, last_result)  = folded_query_level_iterators.next()?;
+            let branch = Branch {
+                last_result,
+                tree_level,
+                query_level_iterator: folded_query_level_iterators,
+                branch_size: branch.len() as u32,
+            };
+            positions.push(branch);
+        }
+    }
+
+    Ok(positions)
+}
+
+fn set_compute_candidates<'t>(
+    ctx: &'t dyn Context<'t>,
+    branches: &Vec<Vec<Vec<Query>>>,
+    allowed_candidates: &RoaringBitmap,
+) -> anyhow::Result<RoaringBitmap>
+{
+    let mut branches_heap = initialize_query_level_iterators(ctx, branches)?;
+    let lowest_level = TreeLevel::min_value();
+
+    while let Some(mut branch) = branches_heap.peek_mut() {
+        let is_lowest_level = branch.tree_level == lowest_level;
+        match branch.last_result.as_mut() {
+            Some((_, _, candidates)) => {
+                candidates.intersect_with(&allowed_candidates);
+                if candidates.len() > 0 && is_lowest_level {
+                    // we have candidates, but we can't dig deeper, return candidates.
+                    return Ok(std::mem::take(candidates));
+                } else if candidates.len() > 0 {
+                    // we have candidates, lets dig deeper in levels.
+                    let mut query_level_iterator = branch.query_level_iterator.dig(ctx)?;
+                    let (tree_level, last_result) = query_level_iterator.next()?;
+                    branch.query_level_iterator = query_level_iterator;
+                    branch.tree_level = tree_level;
+                    branch.last_result = last_result;
+                } else {
+                    // we don't have candidates, get next interval.
+                    let (_, last_result) = branch.query_level_iterator.next()?;
+                    branch.last_result = last_result;
+                }
+            },
+            // None = no candidates to find.
+            None => return Ok(RoaringBitmap::new()),
+        }
+    }
+
+    // we made all iterations without finding anything.
+    Ok(RoaringBitmap::new())
+}
+
 fn linear_compute_candidates(
     ctx: &dyn Context,
     branches: &Vec<Vec<Vec<Query>>>,

milli/src/search/criteria/final.rs

@@ -19,13 +19,13 @@ pub struct FinalResult {
 }
 
 pub struct Final<'t> {
-    ctx: &'t dyn Context,
+    ctx: &'t dyn Context<'t>,
     parent: Box<dyn Criterion + 't>,
     wdcache: WordDerivationsCache,
 }
 
 impl<'t> Final<'t> {
-    pub fn new(ctx: &'t dyn Context, parent: Box<dyn Criterion + 't>) -> Final<'t> {
+    pub fn new(ctx: &'t dyn Context<'t>, parent: Box<dyn Criterion + 't>) -> Final<'t> {
         Final { ctx, parent, wdcache: WordDerivationsCache::new() }
     }
 

milli/src/search/criteria/mod.rs

@@ -4,7 +4,7 @@ use std::borrow::Cow;
 use anyhow::bail;
 use roaring::RoaringBitmap;
 
-use crate::search::{word_derivations, WordDerivationsCache};
+use crate::{TreeLevel, search::{word_derivations, WordDerivationsCache}};
 use crate::{Index, DocumentId};
 
 use super::query_tree::{Operation, Query, QueryKind};
@@ -64,7 +64,7 @@ impl Default for Candidates {
     }
 }
 
-pub trait Context {
+pub trait Context<'c> {
     fn documents_ids(&self) -> heed::Result<RoaringBitmap>;
     fn word_docids(&self, word: &str) -> heed::Result<Option<RoaringBitmap>>;
     fn word_prefix_docids(&self, word: &str) -> heed::Result<Option<RoaringBitmap>>;
@@ -73,6 +73,8 @@ pub trait Context {
     fn words_fst<'t>(&self) -> &'t fst::Set<Cow<[u8]>>;
     fn in_prefix_cache(&self, word: &str) -> bool;
     fn docid_words_positions(&self, docid: DocumentId) -> heed::Result<HashMap<String, RoaringBitmap>>;
+    fn word_position_iterator(&self, word: &str, level: TreeLevel, in_prefix_cache: bool, left: Option<u32>, right: Option<u32>) -> heed::Result<Box<dyn Iterator<Item =heed::Result<((&'c str, TreeLevel, u32, u32), RoaringBitmap)>> + 'c>>;
+    fn word_position_last_level(&self, word: &str, in_prefix_cache: bool) -> heed::Result<Option<TreeLevel>>;
 }
 pub struct CriteriaBuilder<'t> {
     rtxn: &'t heed::RoTxn<'t>,
@@ -81,7 +83,7 @@ pub struct CriteriaBuilder<'t> {
     words_prefixes_fst: fst::Set<Cow<'t, [u8]>>,
 }
 
-impl<'a> Context for CriteriaBuilder<'a> {
+impl<'c> Context<'c> for CriteriaBuilder<'c> {
     fn documents_ids(&self) -> heed::Result<RoaringBitmap> {
         self.index.documents_ids(self.rtxn)
     }
@@ -120,6 +122,40 @@ impl<'a> Context for CriteriaBuilder<'a> {
         }
         Ok(words_positions)
     }
+
+    fn word_position_iterator(&self, word: &str, level: TreeLevel, in_prefix_cache: bool, left: Option<u32>, right: Option<u32>) -> heed::Result<Box<dyn Iterator<Item =heed::Result<((&'c str, TreeLevel, u32, u32), RoaringBitmap)>> + 'c>> {
+        let range = {
+            let left = left.unwrap_or(u32::min_value());
+            let right = right.unwrap_or(u32::max_value());
+            let left = (word, level, left, left);
+            let right = (word, level, right, right);
+            left..=right
+        };
+        let db = match in_prefix_cache {
+            true => self.index.word_prefix_level_position_docids,
+            false => self.index.word_level_position_docids,
+        };
+
+        Ok(Box::new(db.range(self.rtxn, &range)?))
+    }
+
+    fn word_position_last_level(&self, word: &str, in_prefix_cache: bool) -> heed::Result<Option<TreeLevel>> {
+        let range = {
+            let left = (word, TreeLevel::min_value(), u32::min_value(), u32::min_value());
+            let right = (word, TreeLevel::max_value(), u32::max_value(), u32::max_value());
+            left..=right
+        };
+        let db = match in_prefix_cache {
+            true => self.index.word_prefix_level_position_docids,
+            false => self.index.word_level_position_docids,
+        };
+        let last_level = db
+            .remap_data_type::<heed::types::DecodeIgnore>()
+            .range(self.rtxn, &range)?.last().transpose()?
+            .map(|((_, level, _, _), _)| level);
+
+        Ok(last_level)
+    }
 }
 
 impl<'t> CriteriaBuilder<'t> {
@@ -354,7 +390,7 @@ pub mod test {
         docid_words: HashMap<u32, Vec<String>>,
     }
 
-    impl<'a> Context for TestContext<'a> {
+    impl<'c> Context<'c> for TestContext<'c> {
         fn documents_ids(&self) -> heed::Result<RoaringBitmap> {
             Ok(self.word_docids.iter().fold(RoaringBitmap::new(), |acc, (_, docids)| acc | docids))
         }
@@ -397,6 +433,14 @@ pub mod test {
                 Ok(HashMap::new())
             }
         }
+
+        fn word_position_iterator(&self, _word: &str, _level: TreeLevel, _in_prefix_cache: bool, _left: Option<u32>, _right: Option<u32>) -> heed::Result<Box<dyn Iterator<Item =heed::Result<((&'c str, TreeLevel, u32, u32), RoaringBitmap)>> + 'c>> {
+            todo!()
+        }
+
+        fn word_position_last_level(&self, _word: &str, _in_prefix_cache: bool) -> heed::Result<Option<TreeLevel>> {
+            todo!()
+        }
     }
 
     impl<'a> Default for TestContext<'a> {

milli/src/search/criteria/proximity.rs

@@ -13,7 +13,7 @@ use super::{Criterion, CriterionResult, Context, query_docids, query_pair_proxim
 type Cache = HashMap<(Operation, u8), Vec<(Query, Query, RoaringBitmap)>>;
 
 pub struct Proximity<'t> {
-    ctx: &'t dyn Context,
+    ctx: &'t dyn Context<'t>,
     /// ((max_proximity, query_tree), allowed_candidates)
     state: Option<(Option<(usize, Operation)>, RoaringBitmap)>,
     proximity: u8,
@@ -24,7 +24,7 @@ pub struct Proximity<'t> {
 }
 
 impl<'t> Proximity<'t> {
-    pub fn new(ctx: &'t dyn Context, parent: Box<dyn Criterion + 't>) -> Self {
+    pub fn new(ctx: &'t dyn Context<'t>, parent: Box<dyn Criterion + 't>) -> Self {
         Proximity {
             ctx,
             state: None,

milli/src/search/criteria/typo.rs

@@ -9,7 +9,7 @@ use crate::search::{word_derivations, WordDerivationsCache};
 use super::{Candidates, Criterion, CriterionResult, Context, query_docids, query_pair_proximity_docids};
 
 pub struct Typo<'t> {
-    ctx: &'t dyn Context,
+    ctx: &'t dyn Context<'t>,
     query_tree: Option<(usize, Operation)>,
     number_typos: u8,
     candidates: Candidates,
@@ -19,7 +19,7 @@ pub struct Typo<'t> {
 }
 
 impl<'t> Typo<'t> {
-    pub fn new(ctx: &'t dyn Context, parent: Box<dyn Criterion + 't>) -> Self {
+    pub fn new(ctx: &'t dyn Context<'t>, parent: Box<dyn Criterion + 't>) -> Self {
         Typo {
             ctx,
             query_tree: None,

milli/src/search/criteria/words.rs

@@ -8,7 +8,7 @@ use crate::search::query_tree::Operation;
 use super::{resolve_query_tree, Criterion, CriterionResult, Context, WordDerivationsCache};
 
 pub struct Words<'t> {
-    ctx: &'t dyn Context,
+    ctx: &'t dyn Context<'t>,
     query_trees: Vec<Operation>,
     candidates: Option<RoaringBitmap>,
     bucket_candidates: RoaringBitmap,
@@ -17,7 +17,7 @@ pub struct Words<'t> {
 }
 
 impl<'t> Words<'t> {
-    pub fn new(ctx: &'t dyn Context, parent: Box<dyn Criterion + 't>) -> Self {
+    pub fn new(ctx: &'t dyn Context<'t>, parent: Box<dyn Criterion + 't>) -> Self {
         Words {
             ctx,
             query_trees: Vec::default(),

milli/src/tree_level.rs

@@ -21,6 +21,10 @@ impl TreeLevel {
     pub const fn min_value() -> TreeLevel {
         TreeLevel(0)
     }
+
+    pub fn saturating_sub(&self, lhs: u8) -> TreeLevel {
+        TreeLevel(self.0.saturating_sub(lhs))
+    }
 }
 
 impl Into<u8> for TreeLevel {