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Summary: # Introduce early-stop controls for IVF search This PR adds optional early-stop controls to IVF search through `SearchParametersIVF`. IVF search looks in a sequence of buckets. Normally it keeps looking until it has checked all requested buckets. This PR adds a few ways to stop earlier: - stop after enough candidate vectors have been checked, - stop FastScan after enough buckets have been checked, - stop range search after several nearby buckets produce no results. All new fields default to disabled, so existing searches keep their current behavior unless callers opt in. ## New SearchParametersIVF fields Default values: | Field | Default | Effect | |---|---:|---| | `ensure_topk_full` | `false` | disabled; keep the existing hard `max_codes` behavior | | `max_lists_num` | `0` | disabled; FastScan is bounded only by `nprobe` | | `max_empty_result_buckets` | `0` | disabled; range search scans all requested probes | `ensure_topk_full` For k-NN search, `max_codes` limits how many candidate vectors are scanned. With `ensure_topk_full=false`, the search stops when the budget is reached. With `ensure_topk_full=true`, very small budgets become less aggressive: `max_codes` is treated as at least `k` post-filter scans. This helps when `max_codes < k`, or when an `IDSelector` filters out many candidates before a distance is computed. In the generic IVF path this is supported for `parallel_mode` 0 and 3. In FastScan k-NN it is supported by the per-query implementations 10 and 11. `max_lists_num` FastScan k-NN can also stop after visiting a limited number of inverted lists. `0` means disabled. With `ensure_topk_full`, this list budget is treated as at least `k` lists. This is only used by the FastScan per-query path (`search_implem_10`, also used for implementation 11). When FastScan is left on `implem = 0`, setting an early-stop k-NN option makes the dispatcher choose the per-query implementation automatically. If an incompatible FastScan implementation is selected explicitly, Faiss throws instead of ignoring the option. `max_empty_result_buckets` This is for range search. It stops probing a query after that many consecutive probed lists add no in-radius results. The counter resets as soon as a list adds at least one result. `0` means disabled. Setting this trades recall for less work: once nearby buckets repeatedly produce no hits, farther buckets are less likely to help. The generic IVF range path supports this in `parallel_mode == 0`. FastScan range search also supports it through implementation 10. With `implem = 0`, FastScan selects implementation 10 automatically when this option is set; explicit incompatible implementations throw. ## Selector-aware scan accounting This PR adds `InvertedListScannerStats`, returned by inverted-list scanner methods. It currently reports: - `scan_cnt`: number of distances actually computed, - `nheap_updates`: number of result updates. The important behavior change is that `IndexIVFStats::ndis` now uses `scan_cnt`. With an `IDSelector`, candidates rejected by the selector are not counted as computed distances. Without a selector, this matches the previous count because every scanned code reaches distance computation. This same post-filter count is used by `ensure_topk_full`, so a restrictive selector no longer consumes the search budget with candidates that were never eligible for the result heap. ## FastScan behavior FastScan k-NN now applies `max_codes`, `max_lists_num`, and `ensure_topk_full` in the per-query implementation. The code keeps separate counters per query, so multi-query batches have independent budgets. For `max_codes`, FastScan uses the result handler's scanned-row count. This means filtered-out rows do not consume the code budget. FastScan range search rejects k-NN-only options (`max_codes`, `max_lists_num`, and `ensure_topk_full`). It accepts `max_empty_result_buckets` when the selected implementation can preserve per-query probe order. ## API exposure The new fields are exposed through: - C++ `SearchParametersIVF`, - Python bindings, - the C API. The statistics is tracked via `InvertedListScanner::scan_codes(..., ResultHandler& handler)` call. In order to make it work inside `IndexIVF::search()`, it has been decided to transition it into this particular override of `InvertedListScanner::scan_codes()`. As a result, non-`ResultHandler` version of `scan_codes()` has been marked as non-virtual, so the custom `InvertedListScanner` implementations should override `ResultHandler`-based versions only. Another consequence is that `IndexIVFPQFastScanScanner` and `IndexIVFRaBitQFastScanScanner` accept only `HeapResultHandler` types of `ResultHandler`. These are the compromises that had to be made. ## Tests The tests cover: - default parameters preserving baseline k-NN and range-search results, - `ensure_topk_full` filling more result slots under tight budgets, - selector-aware `IndexIVFStats::ndis`, - range-search early exit and counter reset behavior, - unsupported parallel modes and FastScan implementations, - FastScan k-NN and range-search early-stop behavior, - Python and C API field exposure. Pull Request resolved: https://github.com/facebookresearch/faiss/pull/5160 Reviewed By: limqiying Differential Revision: D103044128 Pulled By: mnorris11 fbshipit-source-id: 80f1241c13ffc8173a3da0f2974fa9b6dd318890
194 lines
5.5 KiB
C++
194 lines
5.5 KiB
C++
/*
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* Copyright (c) Meta Platforms, Inc. and affiliates.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*/
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// -*- c++ -*-
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#include "IndexIVF_c.h"
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#include <faiss/IndexIVF.h>
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#include "Clustering_c.h"
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#include "Index_c.h"
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#include "impl/AuxIndexStructures_c.h"
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#include "macros_impl.h"
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using faiss::IndexIVF;
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using faiss::IndexIVFStats;
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using faiss::SearchParametersIVF;
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/// SearchParametersIVF definitions
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DEFINE_DESTRUCTOR(SearchParametersIVF)
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DEFINE_SEARCH_PARAMETERS_DOWNCAST(SearchParametersIVF)
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int faiss_SearchParametersIVF_new(FaissSearchParametersIVF** p_sp) {
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try {
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SearchParametersIVF* sp = new SearchParametersIVF;
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*p_sp = reinterpret_cast<FaissSearchParametersIVF*>(sp);
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}
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CATCH_AND_HANDLE
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}
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int faiss_SearchParametersIVF_new_with(
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FaissSearchParametersIVF** p_sp,
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FaissIDSelector* sel,
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size_t nprobe,
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size_t max_codes) {
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try {
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SearchParametersIVF* sp = new SearchParametersIVF;
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sp->sel = reinterpret_cast<faiss::IDSelector*>(sel);
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sp->nprobe = nprobe;
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sp->max_codes = max_codes;
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*p_sp = reinterpret_cast<FaissSearchParametersIVF*>(sp);
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}
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CATCH_AND_HANDLE
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}
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DEFINE_GETTER_PERMISSIVE(SearchParametersIVF, const FaissIDSelector*, sel)
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DEFINE_GETTER(SearchParametersIVF, size_t, nprobe)
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DEFINE_SETTER(SearchParametersIVF, size_t, nprobe)
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DEFINE_GETTER(SearchParametersIVF, size_t, max_codes)
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DEFINE_SETTER(SearchParametersIVF, size_t, max_codes)
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DEFINE_GETTER(SearchParametersIVF, size_t, max_lists_num)
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DEFINE_SETTER(SearchParametersIVF, size_t, max_lists_num)
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DEFINE_GETTER(SearchParametersIVF, int, ensure_topk_full)
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DEFINE_SETTER_STATIC(SearchParametersIVF, bool, int, ensure_topk_full)
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DEFINE_GETTER(SearchParametersIVF, size_t, max_empty_result_buckets)
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DEFINE_SETTER(SearchParametersIVF, size_t, max_empty_result_buckets)
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/// IndexIVF definitions
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DEFINE_DESTRUCTOR(IndexIVF)
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DEFINE_INDEX_DOWNCAST(IndexIVF)
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/// number of possible key values
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DEFINE_GETTER(IndexIVF, size_t, nlist)
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/// number of probes at query time
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DEFINE_GETTER(IndexIVF, size_t, nprobe)
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DEFINE_SETTER(IndexIVF, size_t, nprobe)
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/// quantizer that maps vectors to inverted lists
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DEFINE_GETTER_PERMISSIVE(IndexIVF, FaissIndex*, quantizer)
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/**
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* = 0: use the quantizer as index in a kmeans training
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* = 1: just pass on the training set to the train() of the quantizer
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* = 2: kmeans training on a flat index + add the centroids to the quantizer
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*/
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DEFINE_GETTER(IndexIVF, char, quantizer_trains_alone)
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/// whether object owns the quantizer
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DEFINE_GETTER(IndexIVF, int, own_fields)
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DEFINE_SETTER(IndexIVF, int, own_fields)
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using faiss::IndexIVF;
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int faiss_IndexIVF_merge_from(
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FaissIndexIVF* index,
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FaissIndexIVF* other,
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idx_t add_id) {
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try {
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reinterpret_cast<IndexIVF*>(index)->merge_from(
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*reinterpret_cast<IndexIVF*>(other), add_id);
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}
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CATCH_AND_HANDLE
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}
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int faiss_IndexIVF_copy_subset_to(
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const FaissIndexIVF* index,
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FaissIndexIVF* other,
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int subset_type,
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idx_t a1,
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idx_t a2) {
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try {
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reinterpret_cast<const IndexIVF*>(index)->copy_subset_to(
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*reinterpret_cast<IndexIVF*>(other),
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static_cast<faiss::InvertedLists::subset_type_t>(subset_type),
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a1,
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a2);
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}
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CATCH_AND_HANDLE
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}
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int faiss_IndexIVF_search_preassigned(
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const FaissIndexIVF* index,
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idx_t n,
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const float* x,
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idx_t k,
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const idx_t* assign,
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const float* centroid_dis,
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float* distances,
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idx_t* labels,
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int store_pairs) {
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try {
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reinterpret_cast<const IndexIVF*>(index)->search_preassigned(
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n, x, k, assign, centroid_dis, distances, labels, store_pairs);
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}
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CATCH_AND_HANDLE
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}
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size_t faiss_IndexIVF_get_list_size(
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const FaissIndexIVF* index,
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size_t list_no) {
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return reinterpret_cast<const IndexIVF*>(index)->get_list_size(list_no);
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}
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int faiss_IndexIVF_make_direct_map(
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FaissIndexIVF* index,
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int new_maintain_direct_map) {
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try {
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reinterpret_cast<IndexIVF*>(index)->make_direct_map(
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static_cast<bool>(new_maintain_direct_map));
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}
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CATCH_AND_HANDLE
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}
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double faiss_IndexIVF_imbalance_factor(const FaissIndexIVF* index) {
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return reinterpret_cast<const IndexIVF*>(index)
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->invlists->imbalance_factor();
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}
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/// display some stats about the inverted lists
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void faiss_IndexIVF_print_stats(const FaissIndexIVF* index) {
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reinterpret_cast<const IndexIVF*>(index)->invlists->print_stats();
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}
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/// get inverted lists ids
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void faiss_IndexIVF_invlists_get_ids(
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const FaissIndexIVF* index,
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size_t list_no,
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idx_t* invlist) {
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const idx_t* list =
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reinterpret_cast<const IndexIVF*>(index)->invlists->get_ids(
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list_no);
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size_t list_size =
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reinterpret_cast<const IndexIVF*>(index)->get_list_size(list_no);
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memcpy(invlist, list, list_size * sizeof(idx_t));
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}
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int faiss_IndexIVF_train_encoder(
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FaissIndexIVF* index,
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idx_t n,
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const float* x,
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const idx_t* assign) {
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try {
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reinterpret_cast<IndexIVF*>(index)->train_encoder(n, x, assign);
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}
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CATCH_AND_HANDLE
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}
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void faiss_IndexIVFStats_reset(FaissIndexIVFStats* stats) {
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reinterpret_cast<IndexIVFStats*>(stats)->reset();
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}
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FaissIndexIVFStats* faiss_get_indexIVF_stats() {
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return reinterpret_cast<FaissIndexIVFStats*>(&faiss::indexIVF_stats);
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}
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