MeiliSearch/meilisearch-core/src/query_tree.rs

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use std::borrow::Cow;
use std::collections::HashMap;
use std::hash::{Hash, Hasher};
use std::ops::Range;
use std::time::Instant;
use std::{cmp, fmt, iter::once};
use fst::{IntoStreamer, Streamer};
use itertools::{EitherOrBoth, merge_join_by};
use meilisearch_tokenizer::split_query_string;
use sdset::{Set, SetBuf, SetOperation};
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use log::debug;
use crate::database::MainT;
use crate::{store, DocumentId, DocIndex, MResult};
use crate::automaton::{normalize_str, build_dfa, build_prefix_dfa, build_exact_dfa};
use crate::QueryWordsMapper;
#[derive(Clone, PartialEq, Eq, Hash)]
pub enum Operation {
And(Vec<Operation>),
Or(Vec<Operation>),
Query(Query),
}
impl fmt::Debug for Operation {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fn pprint_tree(f: &mut fmt::Formatter<'_>, op: &Operation, depth: usize) -> fmt::Result {
match op {
Operation::And(children) => {
writeln!(f, "{:1$}AND", "", depth * 2)?;
children.iter().try_for_each(|c| pprint_tree(f, c, depth + 1))
},
Operation::Or(children) => {
writeln!(f, "{:1$}OR", "", depth * 2)?;
children.iter().try_for_each(|c| pprint_tree(f, c, depth + 1))
},
Operation::Query(query) => writeln!(f, "{:2$}{:?}", "", query, depth * 2),
}
}
pprint_tree(f, self, 0)
}
}
impl Operation {
fn tolerant(id: QueryId, prefix: bool, s: &str) -> Operation {
Operation::Query(Query { id, prefix, exact: true, kind: QueryKind::Tolerant(s.to_string()) })
}
fn non_tolerant(id: QueryId, prefix: bool, s: &str) -> Operation {
Operation::Query(Query { id, prefix, exact: true, kind: QueryKind::NonTolerant(s.to_string()) })
}
fn phrase2(id: QueryId, prefix: bool, (left, right): (&str, &str)) -> Operation {
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let kind = QueryKind::Phrase(vec![left.to_owned(), right.to_owned()]);
Operation::Query(Query { id, prefix, exact: true, kind })
}
}
pub type QueryId = usize;
#[derive(Clone, Eq)]
pub struct Query {
pub id: QueryId,
pub prefix: bool,
pub exact: bool,
pub kind: QueryKind,
}
impl PartialEq for Query {
fn eq(&self, other: &Self) -> bool {
self.prefix == other.prefix && self.kind == other.kind
}
}
impl Hash for Query {
fn hash<H: Hasher>(&self, state: &mut H) {
self.prefix.hash(state);
self.kind.hash(state);
}
}
#[derive(Clone, PartialEq, Eq, Hash)]
pub enum QueryKind {
Tolerant(String),
NonTolerant(String),
Phrase(Vec<String>),
}
impl fmt::Debug for Query {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let Query { id, prefix, kind, .. } = self;
let prefix = if *prefix { String::from("Prefix") } else { String::default() };
match kind {
QueryKind::NonTolerant(word) => {
f.debug_struct(&(prefix + "NonTolerant")).field("id", &id).field("word", &word).finish()
},
QueryKind::Tolerant(word) => {
f.debug_struct(&(prefix + "Tolerant")).field("id", &id).field("word", &word).finish()
},
QueryKind::Phrase(words) => {
f.debug_struct(&(prefix + "Phrase")).field("id", &id).field("words", &words).finish()
},
}
}
}
#[derive(Debug, Default)]
pub struct PostingsList {
docids: SetBuf<DocumentId>,
matches: SetBuf<DocIndex>,
}
pub struct Context {
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pub words_set: fst::Set,
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pub stop_words: fst::Set,
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pub synonyms: store::Synonyms,
pub postings_lists: store::PostingsLists,
pub prefix_postings_lists: store::PrefixPostingsListsCache,
}
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fn split_best_frequency<'a>(reader: &heed::RoTxn<MainT>, ctx: &Context, word: &'a str) -> MResult<Option<(&'a str, &'a str)>> {
let chars = word.char_indices().skip(1);
let mut best = None;
for (i, _) in chars {
let (left, right) = word.split_at(i);
let left_freq = ctx.postings_lists
.postings_list(reader, left.as_bytes())?
.map(|p| p.docids.len())
.unwrap_or(0);
let right_freq = ctx.postings_lists
.postings_list(reader, right.as_bytes())?
.map(|p| p.docids.len())
.unwrap_or(0);
let min_freq = cmp::min(left_freq, right_freq);
if min_freq != 0 && best.map_or(true, |(old, _, _)| min_freq > old) {
best = Some((min_freq, left, right));
}
}
Ok(best.map(|(_, l, r)| (l, r)))
}
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fn fetch_synonyms(reader: &heed::RoTxn<MainT>, ctx: &Context, words: &[&str]) -> MResult<Vec<Vec<String>>> {
let words = normalize_str(&words.join(" "));
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let set = ctx.synonyms.synonyms(reader, words.as_bytes())?.unwrap_or_default();
let mut strings = Vec::new();
let mut stream = set.stream();
while let Some(input) = stream.next() {
if let Ok(input) = std::str::from_utf8(input) {
let alts = input.split_ascii_whitespace().map(ToOwned::to_owned).collect();
strings.push(alts);
}
}
Ok(strings)
}
fn create_operation<I, F>(iter: I, f: F) -> Operation
where I: IntoIterator<Item=Operation>,
F: Fn(Vec<Operation>) -> Operation,
{
let mut iter = iter.into_iter();
match (iter.next(), iter.next()) {
(Some(first), None) => first,
(first, second) => f(first.into_iter().chain(second).chain(iter).collect()),
}
}
const MAX_NGRAM: usize = 3;
pub fn create_query_tree(
reader: &heed::RoTxn<MainT>,
ctx: &Context,
query: &str,
) -> MResult<(Operation, HashMap<QueryId, Range<usize>>)>
{
let words = split_query_string(query).map(str::to_lowercase);
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let words = words.filter(|w| !ctx.stop_words.contains(w));
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let words: Vec<_> = words.enumerate().collect();
let mut mapper = QueryWordsMapper::new(words.iter().map(|(_, w)| w));
fn create_inner(
reader: &heed::RoTxn<MainT>,
ctx: &Context,
mapper: &mut QueryWordsMapper,
words: &[(usize, String)],
) -> MResult<Vec<Operation>>
{
let mut alts = Vec::new();
for ngram in 1..=MAX_NGRAM {
if let Some(group) = words.get(..ngram) {
let mut group_ops = Vec::new();
let tail = &words[ngram..];
let is_last = tail.is_empty();
let mut group_alts = Vec::new();
match group {
[(id, word)] => {
let mut idgen = ((id + 1) * 100)..;
let range = (*id)..id+1;
let phrase = split_best_frequency(reader, ctx, word)?
.map(|ws| {
let id = idgen.next().unwrap();
idgen.next().unwrap();
mapper.declare(range.clone(), id, &[ws.0, ws.1]);
Operation::phrase2(id, is_last, ws)
});
let synonyms = fetch_synonyms(reader, ctx, &[word])?
.into_iter()
.map(|alts| {
let exact = alts.len() == 1;
let id = idgen.next().unwrap();
mapper.declare(range.clone(), id, &alts);
let mut idgen = once(id).chain(&mut idgen);
let iter = alts.into_iter().map(|w| {
let id = idgen.next().unwrap();
let kind = QueryKind::NonTolerant(w);
Operation::Query(Query { id, prefix: false, exact, kind })
});
create_operation(iter, Operation::And)
});
let original = Operation::tolerant(*id, is_last, word);
group_alts.push(original);
group_alts.extend(synonyms.chain(phrase));
},
words => {
let id = words[0].0;
let mut idgen = ((id + 1) * 100_usize.pow(ngram as u32))..;
let range = id..id+ngram;
let words: Vec<_> = words.iter().map(|(_, s)| s.as_str()).collect();
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for synonym in fetch_synonyms(reader, ctx, &words)? {
let exact = synonym.len() == 1;
let id = idgen.next().unwrap();
mapper.declare(range.clone(), id, &synonym);
let mut idgen = once(id).chain(&mut idgen);
let synonym = synonym.into_iter().map(|s| {
let id = idgen.next().unwrap();
let kind = QueryKind::NonTolerant(s);
Operation::Query(Query { id, prefix: false, exact, kind })
});
group_alts.push(create_operation(synonym, Operation::And));
}
let id = idgen.next().unwrap();
let concat = words.concat();
mapper.declare(range.clone(), id, &[&concat]);
group_alts.push(Operation::non_tolerant(id, is_last, &concat));
}
}
group_ops.push(create_operation(group_alts, Operation::Or));
if !tail.is_empty() {
let tail_ops = create_inner(reader, ctx, mapper, tail)?;
group_ops.push(create_operation(tail_ops, Operation::Or));
}
alts.push(create_operation(group_ops, Operation::And));
}
}
Ok(alts)
}
let alternatives = create_inner(reader, ctx, &mut mapper, &words)?;
let operation = Operation::Or(alternatives);
let mapping = mapper.mapping();
Ok((operation, mapping))
}
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct PostingsKey<'o> {
pub query: &'o Query,
pub input: Vec<u8>,
pub distance: u8,
pub is_exact: bool,
}
pub type Postings<'o, 'txn> = HashMap<PostingsKey<'o>, Cow<'txn, Set<DocIndex>>>;
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pub type Cache<'o, 'txn> = HashMap<&'o Operation, Cow<'txn, Set<DocumentId>>>;
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pub struct QueryResult<'o, 'txn> {
pub docids: Cow<'txn, Set<DocumentId>>,
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pub queries: Postings<'o, 'txn>,
}
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pub fn traverse_query_tree<'o, 'txn>(
reader: &'txn heed::RoTxn<MainT>,
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ctx: &Context,
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tree: &'o Operation,
) -> MResult<QueryResult<'o, 'txn>>
{
fn execute_and<'o, 'txn>(
reader: &'txn heed::RoTxn<MainT>,
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ctx: &Context,
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cache: &mut Cache<'o, 'txn>,
postings: &mut Postings<'o, 'txn>,
depth: usize,
operations: &'o [Operation],
) -> MResult<Cow<'txn, Set<DocumentId>>>
{
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debug!("{:1$}AND", "", depth * 2);
let before = Instant::now();
let mut results = Vec::new();
for op in operations {
if cache.get(op).is_none() {
let docids = match op {
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Operation::And(ops) => execute_and(reader, ctx, cache, postings, depth + 1, &ops)?,
Operation::Or(ops) => execute_or(reader, ctx, cache, postings, depth + 1, &ops)?,
Operation::Query(query) => execute_query(reader, ctx, postings, depth + 1, &query)?,
};
cache.insert(op, docids);
}
}
for op in operations {
if let Some(docids) = cache.get(op) {
results.push(docids.as_ref());
}
}
let op = sdset::multi::Intersection::new(results);
let docids = op.into_set_buf();
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debug!("{:3$}--- AND fetched {} documents in {:.02?}", "", docids.len(), before.elapsed(), depth * 2);
Ok(Cow::Owned(docids))
}
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fn execute_or<'o, 'txn>(
reader: &'txn heed::RoTxn<MainT>,
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ctx: &Context,
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cache: &mut Cache<'o, 'txn>,
postings: &mut Postings<'o, 'txn>,
depth: usize,
operations: &'o [Operation],
) -> MResult<Cow<'txn, Set<DocumentId>>>
{
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debug!("{:1$}OR", "", depth * 2);
let before = Instant::now();
let mut results = Vec::new();
for op in operations {
if cache.get(op).is_none() {
let docids = match op {
Operation::And(ops) => execute_and(reader, ctx, cache, postings, depth + 1, &ops)?,
Operation::Or(ops) => execute_or(reader, ctx, cache, postings, depth + 1, &ops)?,
Operation::Query(query) => execute_query(reader, ctx, postings, depth + 1, &query)?,
};
cache.insert(op, docids);
}
}
for op in operations {
if let Some(docids) = cache.get(op) {
results.push(docids.as_ref());
}
}
let op = sdset::multi::Union::new(results);
let docids = op.into_set_buf();
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debug!("{:3$}--- OR fetched {} documents in {:.02?}", "", docids.len(), before.elapsed(), depth * 2);
Ok(Cow::Owned(docids))
}
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fn execute_query<'o, 'txn>(
reader: &'txn heed::RoTxn<MainT>,
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ctx: &Context,
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postings: &mut Postings<'o, 'txn>,
depth: usize,
query: &'o Query,
) -> MResult<Cow<'txn, Set<DocumentId>>>
{
let before = Instant::now();
let Query { prefix, kind, exact, .. } = query;
let docids: Cow<Set<_>> = match kind {
QueryKind::Tolerant(word) => {
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if *prefix && word.len() <= 2 {
let prefix = {
let mut array = [0; 4];
let bytes = word.as_bytes();
array[..bytes.len()].copy_from_slice(bytes);
array
};
// We retrieve the cached postings lists for all
// the words that starts with this short prefix.
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let result = ctx.prefix_postings_lists.prefix_postings_list(reader, prefix)?.unwrap_or_default();
let key = PostingsKey { query, input: word.clone().into_bytes(), distance: 0, is_exact: false };
postings.insert(key, result.matches);
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let prefix_docids = &result.docids;
// We retrieve the exact postings list for the prefix,
// because we must consider these matches as exact.
let result = ctx.postings_lists.postings_list(reader, word.as_bytes())?.unwrap_or_default();
let key = PostingsKey { query, input: word.clone().into_bytes(), distance: 0, is_exact: true };
postings.insert(key, result.matches);
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let exact_docids = &result.docids;
let before = Instant::now();
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let docids = sdset::duo::Union::new(prefix_docids, exact_docids).into_set_buf();
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debug!("{:4$}prefix docids ({} and {}) construction took {:.02?}",
"", prefix_docids.len(), exact_docids.len(), before.elapsed(), depth * 2);
Cow::Owned(docids)
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} else {
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let dfa = if *prefix { build_prefix_dfa(word) } else { build_dfa(word) };
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let byte = word.as_bytes()[0];
let mut stream = if byte == u8::max_value() {
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ctx.words_set.search(&dfa).ge(&[byte]).into_stream()
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} else {
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ctx.words_set.search(&dfa).ge(&[byte]).lt(&[byte + 1]).into_stream()
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};
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let before = Instant::now();
let mut results = Vec::new();
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while let Some(input) = stream.next() {
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if let Some(result) = ctx.postings_lists.postings_list(reader, input)? {
let distance = dfa.eval(input).to_u8();
let is_exact = *exact && distance == 0 && input.len() == word.len();
results.push(result.docids);
let key = PostingsKey { query, input: input.to_owned(), distance, is_exact };
postings.insert(key, result.matches);
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}
}
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debug!("{:3$}docids retrieval ({:?}) took {:.02?}", "", results.len(), before.elapsed(), depth * 2);
let before = Instant::now();
let docids = if results.len() > 10 {
let cap = results.iter().map(|dis| dis.len()).sum();
let mut docids = Vec::with_capacity(cap);
for dis in results {
docids.extend_from_slice(&dis);
}
SetBuf::from_dirty(docids)
} else {
let sets = results.iter().map(AsRef::as_ref).collect();
sdset::multi::Union::new(sets).into_set_buf()
};
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debug!("{:2$}docids construction took {:.02?}", "", before.elapsed(), depth * 2);
Cow::Owned(docids)
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}
},
QueryKind::NonTolerant(word) => {
// TODO support prefix and non-prefix exact DFA
let dfa = build_exact_dfa(word);
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let byte = word.as_bytes()[0];
let mut stream = if byte == u8::max_value() {
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ctx.words_set.search(&dfa).ge(&[byte]).into_stream()
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} else {
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ctx.words_set.search(&dfa).ge(&[byte]).lt(&[byte + 1]).into_stream()
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};
let before = Instant::now();
let mut results = Vec::new();
while let Some(input) = stream.next() {
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if let Some(result) = ctx.postings_lists.postings_list(reader, input)? {
let distance = dfa.eval(input).to_u8();
results.push(result.docids);
let key = PostingsKey { query, input: input.to_owned(), distance, is_exact: *exact };
postings.insert(key, result.matches);
}
}
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debug!("{:3$}docids retrieval ({:?}) took {:.02?}", "", results.len(), before.elapsed(), depth * 2);
let before = Instant::now();
let docids = if results.len() > 10 {
let cap = results.iter().map(|dis| dis.len()).sum();
let mut docids = Vec::with_capacity(cap);
for dis in results {
docids.extend_from_slice(&dis);
}
SetBuf::from_dirty(docids)
} else {
let sets = results.iter().map(AsRef::as_ref).collect();
sdset::multi::Union::new(sets).into_set_buf()
};
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debug!("{:2$}docids construction took {:.02?}", "", before.elapsed(), depth * 2);
Cow::Owned(docids)
},
QueryKind::Phrase(words) => {
// TODO support prefix and non-prefix exact DFA
if let [first, second] = words.as_slice() {
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let first = ctx.postings_lists.postings_list(reader, first.as_bytes())?.unwrap_or_default();
let second = ctx.postings_lists.postings_list(reader, second.as_bytes())?.unwrap_or_default();
let iter = merge_join_by(first.matches.as_slice(), second.matches.as_slice(), |a, b| {
let x = (a.document_id, a.attribute, (a.word_index as u32) + 1);
let y = (b.document_id, b.attribute, b.word_index as u32);
x.cmp(&y)
});
let matches: Vec<_> = iter
.filter_map(EitherOrBoth::both)
.flat_map(|(a, b)| once(*a).chain(Some(*b)))
.collect();
let before = Instant::now();
let mut docids: Vec<_> = matches.iter().map(|m| m.document_id).collect();
docids.dedup();
let docids = SetBuf::new(docids).unwrap();
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debug!("{:2$}docids construction took {:.02?}", "", before.elapsed(), depth * 2);
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let matches = Cow::Owned(SetBuf::from_dirty(matches));
let key = PostingsKey { query, input: vec![], distance: 0, is_exact: true };
postings.insert(key, matches);
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Cow::Owned(docids)
} else {
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debug!("{:2$}{:?} skipped", "", words, depth * 2);
Cow::default()
}
},
};
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debug!("{:4$}{:?} fetched {:?} documents in {:.02?}", "", query, docids.len(), before.elapsed(), depth * 2);
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Ok(docids)
}
let mut cache = Cache::new();
let mut postings = Postings::new();
let docids = match tree {
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Operation::And(ops) => execute_and(reader, ctx, &mut cache, &mut postings, 0, &ops)?,
Operation::Or(ops) => execute_or(reader, ctx, &mut cache, &mut postings, 0, &ops)?,
Operation::Query(query) => execute_query(reader, ctx, &mut postings, 0, &query)?,
};
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Ok(QueryResult { docids, queries: postings })
}