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Avoid a prefix-related worst-case scenario in the proximity criterion

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This commit is contained in:
Loïc Lecrenier 2022-12-08 11:53:21 +01:00
parent a8defb585b
commit 777b387dc4
4 changed files with 108 additions and 50 deletions
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124
milli/src/search/criteria/mod.rs
View File

@ -17,6 +17,7 @@ use super::query_tree::{Operation, PrimitiveQueryPart, Query, QueryKind};
use super::CriterionImplementationStrategy;
use crate::search::criteria::geo::Geo;
use crate::search::{word_derivations, Distinct, WordDerivationsCache};
use crate::update::{MAX_LENGTH_FOR_PREFIX_PROXIMITY_DB, MAX_PROXIMITY_FOR_PREFIX_PROXIMITY_DB};
use crate::{AscDesc as AscDescName, DocumentId, FieldId, Index, Member, Result};
mod asc_desc;
@ -653,14 +654,30 @@ fn query_pair_proximity_docids(
match (&left.kind, &right.kind) {
(QueryKind::Exact { word: left, .. }, QueryKind::Exact { word: right, .. }) => {
if prefix {
match word_prefix_pair_overall_proximity_docids(
ctx,
left.as_str(),
right.as_str(),
proximity,
)? {
Some(docids) => Ok(docids),
None => {
// There are three distinct cases which we need to distinguish regarding the prefix `right`:
//
// 1. `right` is not in any prefix cache because it is not the prefix of many words
// (and thus, it doesn't have many word derivations)
// 2. `right` is in the prefix cache but cannot be found in the "word prefix pair proximity" databases either
// because it is too long or because the given proximity is too high.
// 3. `right` is in the prefix cache and can be found in the "word prefix pair proximity" databases
//
// The three cases are handled as follows:
// 1. We manually retrieve all the word derivations of `right` and check the `word_pair_proximity`
// database for each of them.
// 2. It would be too expensive to apply the same strategy as (1), therefore, we "disable" the
// proximity ranking rule for the prefixes of the right word. This is done as follows:
// 1. Only find the documents where left is in proximity to the exact (ie non-prefix) right word
// 2. Otherwise, assume that their proximity in all the documents in which they coexist is >= 8
//
// 3. Query the prefix proximity databases.
match (
ctx.in_prefix_cache(right),
right.len() <= MAX_LENGTH_FOR_PREFIX_PROXIMITY_DB
&& proximity <= MAX_PROXIMITY_FOR_PREFIX_PROXIMITY_DB,
) {
// Case 1: not in prefix cache
(false, _) => {
let r_words = word_derivations(right, true, 0, ctx.words_fst(), wdcache)?;
all_word_pair_overall_proximity_docids(
ctx,
@ -669,40 +686,91 @@ fn query_pair_proximity_docids(
proximity,
)
}
// Case 2: in prefix cache but either the prefix length or the proximity makes it impossible to
// query the prefix proximity databases.
(true, false) => {
// To "save" the relevancy a little bit, we still find the documents where the
// exact (i.e. non-prefix) right word is in the given proximity to the left word.
Ok(word_pair_overall_proximity_docids(
ctx,
left.as_str(),
right.as_str(),
proximity,
)?
.unwrap_or_default())
}
// Case 3: in prefix cache, short enough, and proximity is low enough
(true, true) => Ok(word_prefix_pair_overall_proximity_docids(
ctx,
left.as_str(),
right.as_str(),
proximity,
)?
.unwrap_or_default()),
}
} else {
Ok(ctx
.word_pair_proximity_docids(left.as_str(), right.as_str(), proximity)?
.unwrap_or_default())
Ok(word_pair_overall_proximity_docids(
ctx,
left.as_str(),
right.as_str(),
proximity,
)?
.unwrap_or_default())
}
}
(QueryKind::Tolerant { typo, word: left }, QueryKind::Exact { word: right, .. }) => {
let l_words =
word_derivations(left, false, *typo, ctx.words_fst(), wdcache)?.to_owned();
if prefix {
let mut docids = RoaringBitmap::new();
for (left, _) in l_words {
let current_docids = match word_prefix_pair_overall_proximity_docids(
ctx,
left.as_str(),
right.as_str(),
proximity,
)? {
Some(docids) => Ok(docids),
None => {
let r_words =
word_derivations(right, true, 0, ctx.words_fst(), wdcache)?;
all_word_pair_overall_proximity_docids(
// The logic here is almost identical to the one in the previous match branch.
// The difference is that we fetch the docids for each derivation of the left word.
match (
ctx.in_prefix_cache(right),
right.len() <= MAX_LENGTH_FOR_PREFIX_PROXIMITY_DB
&& proximity <= MAX_PROXIMITY_FOR_PREFIX_PROXIMITY_DB,
) {
// Case 1: not in prefix cache
(false, _) => {
let mut docids = RoaringBitmap::new();
let r_words = word_derivations(right, true, 0, ctx.words_fst(), wdcache)?;
for (left, _) in l_words {
docids |= all_word_pair_overall_proximity_docids(
ctx,
&[(left, 0)],
r_words,
proximity,
)
)?;
}
}?;
docids |= current_docids;
Ok(docids)
}
// Case 2: in prefix cache but either the prefix length or the proximity makes it impossible to
// query the prefix proximity databases.
(true, false) => {
// To "save" the relevancy a little bit, we still find the documents where the
// exact (i.e. non-prefix) right word is in proximity to any derivation of the left word.
let mut candidates = RoaringBitmap::new();
for (left, _) in l_words {
candidates |= ctx
.word_pair_proximity_docids(&left, right, proximity)?
.unwrap_or_default();
}
Ok(candidates)
}
// Case 3: in prefix cache, short enough, and proximity is low enough
(true, true) => {
let mut docids = RoaringBitmap::new();
for (left, _) in l_words {
docids |= word_prefix_pair_overall_proximity_docids(
ctx,
left.as_str(),
right.as_str(),
proximity,
)?
.unwrap_or_default();
}
Ok(docids)
}
}
Ok(docids)
} else {
all_word_pair_overall_proximity_docids(ctx, &l_words, &[(right, 0)], proximity)
}

3
milli/src/search/criteria/proximity.rs
View File

@ -590,3 +590,6 @@ fn resolve_plane_sweep_candidates(
Ok(candidates)
}
#[cfg(test)]
mod tests {}

5
milli/src/update/mod.rs
View File

@ -7,7 +7,10 @@ pub use self::index_documents::{
DocumentAdditionResult, DocumentId, IndexDocuments, IndexDocumentsConfig, IndexDocumentsMethod,
};
pub use self::indexer_config::IndexerConfig;
pub use self::prefix_word_pairs::PrefixWordPairsProximityDocids;
pub use self::prefix_word_pairs::{
PrefixWordPairsProximityDocids, MAX_LENGTH_FOR_PREFIX_PROXIMITY_DB,
MAX_PROXIMITY_FOR_PREFIX_PROXIMITY_DB,
};
pub use self::settings::{Setting, Settings};
pub use self::update_step::UpdateIndexingStep;
pub use self::word_prefix_docids::WordPrefixDocids;

26
milli/src/update/prefix_word_pairs/mod.rs
View File

@ -14,6 +14,9 @@ mod word_prefix;
pub use prefix_word::index_prefix_word_database;
pub use word_prefix::index_word_prefix_database;
pub const MAX_PROXIMITY_FOR_PREFIX_PROXIMITY_DB: u8 = 4;
pub const MAX_LENGTH_FOR_PREFIX_PROXIMITY_DB: usize = 2;
pub struct PrefixWordPairsProximityDocids<'t, 'u, 'i> {
wtxn: &'t mut heed::RwTxn<'i, 'u>,
index: &'i Index,
@ -32,31 +35,12 @@ impl<'t, 'u, 'i> PrefixWordPairsProximityDocids<'t, 'u, 'i> {
Self {
wtxn,
index,
max_proximity: 4,
max_prefix_length: 2,
max_proximity: MAX_PROXIMITY_FOR_PREFIX_PROXIMITY_DB,
max_prefix_length: MAX_LENGTH_FOR_PREFIX_PROXIMITY_DB,
chunk_compression_type,
chunk_compression_level,
}
}
/// Set the maximum proximity required to make a prefix be part of the words prefixes
/// database. If two words are too far from the threshold the associated documents will
/// not be part of the prefix database.
///
/// Default value is 4. This value must be lower or equal than 7 and will be clamped
/// to this bound otherwise.
pub fn max_proximity(&mut self, value: u8) -> &mut Self {
self.max_proximity = value.max(7);
self
}
/// Set the maximum length the prefix of a word pair is allowed to have to be part of the words
/// prefixes database. If the prefix length is higher than the threshold, the associated documents
/// will not be part of the prefix database.
///
/// Default value is 2.
pub fn max_prefix_length(&mut self, value: usize) -> &mut Self {
self.max_prefix_length = value;
self
}
#[logging_timer::time("WordPrefixPairProximityDocids::{}")]
pub fn execute<'a>(