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packages/leann-backend-hnsw/third_party/faiss/tests/test_merge.cpp

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+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <cstdio>
+#include <random>
+
+#include <gtest/gtest.h>
+
+#include <faiss/IVFlib.h>
+#include <faiss/IndexFlat.h>
+#include <faiss/IndexIVFFlat.h>
+#include <faiss/IndexPreTransform.h>
+#include <faiss/MetaIndexes.h>
+#include <faiss/invlists/OnDiskInvertedLists.h>
+
+#include "test_util.h"
+
+namespace {
+
+pthread_mutex_t temp_file_mutex = PTHREAD_MUTEX_INITIALIZER;
+
+typedef faiss::idx_t idx_t;
+
+// parameters to use for the test
+int d = 64;
+size_t nb = 1000;
+size_t nq = 100;
+int nindex = 4;
+int k = 10;
+int nlist = 40;
+int shard_size = nb / nindex;
+
+struct CommonData {
+    std::vector<float> database;
+    std::vector<float> queries;
+    std::vector<idx_t> ids;
+    faiss::IndexFlatL2 quantizer;
+
+    CommonData() : database(nb * d), queries(nq * d), ids(nb), quantizer(d) {
+        std::mt19937 rng;
+        std::uniform_real_distribution<> distrib;
+        for (size_t i = 0; i < nb * d; i++) {
+            database[i] = distrib(rng);
+        }
+        for (size_t i = 0; i < nq * d; i++) {
+            queries[i] = distrib(rng);
+        }
+        for (int i = 0; i < nb; i++) {
+            ids[i] = 123 + 456 * i;
+        }
+        { // just to train the quantizer
+            faiss::IndexIVFFlat iflat(&quantizer, d, nlist);
+            iflat.train(nb, database.data());
+        }
+    }
+};
+
+CommonData cd;
+std::string temp_filename_template = "/tmp/faiss_tmp_XXXXXX";
+/// perform a search on shards, then merge and search again and
+/// compare results.
+int compare_merged(
+        faiss::IndexShards* index_shards,
+        bool shift_ids,
+        bool standard_merge = true) {
+    std::vector<idx_t> refI(k * nq);
+    std::vector<float> refD(k * nq);
+
+    index_shards->search(nq, cd.queries.data(), k, refD.data(), refI.data());
+    Tempfilename filename(&temp_file_mutex, temp_filename_template);
+
+    std::vector<idx_t> newI(k * nq);
+    std::vector<float> newD(k * nq);
+
+    if (standard_merge) {
+        for (int i = 1; i < nindex; i++) {
+            faiss::ivflib::merge_into(
+                    index_shards->at(0), index_shards->at(i), shift_ids);
+        }
+
+        index_shards->syncWithSubIndexes();
+    } else {
+        std::vector<const faiss::InvertedLists*> lists;
+        faiss::IndexIVF* index0 = nullptr;
+        size_t ntotal = 0;
+        for (int i = 0; i < nindex; i++) {
+            auto index_ivf =
+                    dynamic_cast<faiss::IndexIVF*>(index_shards->at(i));
+            assert(index_ivf);
+            if (i == 0) {
+                index0 = index_ivf;
+            }
+            lists.push_back(index_ivf->invlists);
+            ntotal += index_ivf->ntotal;
+        }
+
+        auto il = new faiss::OnDiskInvertedLists(
+                index0->nlist, index0->code_size, filename.c_str());
+
+        il->merge_from_multiple(lists.data(), lists.size(), shift_ids);
+
+        index0->replace_invlists(il, true);
+        index0->ntotal = ntotal;
+    }
+    // search only on first index
+    index_shards->at(0)->search(
+            nq, cd.queries.data(), k, newD.data(), newI.data());
+
+    size_t ndiff = 0;
+    bool adjust_ids = shift_ids && !standard_merge;
+    for (size_t i = 0; i < k * nq; i++) {
+        idx_t new_id = adjust_ids ? refI[i] % shard_size : refI[i];
+        if (refI[i] != new_id) {
+            ndiff++;
+        }
+    }
+
+    return ndiff;
+}
+
+} // namespace
+
+// test on IVFFlat with implicit numbering
+TEST(MERGE, merge_flat_no_ids) {
+    faiss::IndexShards index_shards(d);
+    index_shards.own_indices = true;
+    for (int i = 0; i < nindex; i++) {
+        index_shards.add_shard(
+                new faiss::IndexIVFFlat(&cd.quantizer, d, nlist));
+    }
+    EXPECT_TRUE(index_shards.is_trained);
+    index_shards.add(nb, cd.database.data());
+    size_t prev_ntotal = index_shards.ntotal;
+    int ndiff = compare_merged(&index_shards, true);
+    EXPECT_EQ(prev_ntotal, index_shards.ntotal);
+    EXPECT_EQ(0, ndiff);
+}
+
+// test on IVFFlat, explicit ids
+TEST(MERGE, merge_flat) {
+    faiss::IndexShards index_shards(d, false, false);
+    index_shards.own_indices = true;
+
+    for (int i = 0; i < nindex; i++) {
+        index_shards.add_shard(
+                new faiss::IndexIVFFlat(&cd.quantizer, d, nlist));
+    }
+
+    EXPECT_TRUE(index_shards.is_trained);
+    index_shards.add_with_ids(nb, cd.database.data(), cd.ids.data());
+    int ndiff = compare_merged(&index_shards, false);
+    EXPECT_GE(0, ndiff);
+}
+
+// test on IVFFlat and a VectorTransform
+TEST(MERGE, merge_flat_vt) {
+    faiss::IndexShards index_shards(d, false, false);
+    index_shards.own_indices = true;
+
+    // here we have to retrain because of the vectorTransform
+    faiss::RandomRotationMatrix rot(d, d);
+    rot.init(1234);
+    faiss::IndexFlatL2 quantizer(d);
+
+    { // just to train the quantizer
+        faiss::IndexIVFFlat iflat(&quantizer, d, nlist);
+        faiss::IndexPreTransform ipt(&rot, &iflat);
+        ipt.train(nb, cd.database.data());
+    }
+
+    for (int i = 0; i < nindex; i++) {
+        faiss::IndexPreTransform* ipt = new faiss::IndexPreTransform(
+                new faiss::RandomRotationMatrix(rot),
+                new faiss::IndexIVFFlat(&quantizer, d, nlist));
+        ipt->own_fields = true;
+        index_shards.add_shard(ipt);
+    }
+    EXPECT_TRUE(index_shards.is_trained);
+    index_shards.add_with_ids(nb, cd.database.data(), cd.ids.data());
+    size_t prev_ntotal = index_shards.ntotal;
+    int ndiff = compare_merged(&index_shards, false);
+    EXPECT_EQ(prev_ntotal, index_shards.ntotal);
+    EXPECT_GE(0, ndiff);
+}
+
+// put the merged invfile on disk
+TEST(MERGE, merge_flat_ondisk) {
+    faiss::IndexShards index_shards(d, false, false);
+    index_shards.own_indices = true;
+    Tempfilename filename(&temp_file_mutex, temp_filename_template);
+
+    for (int i = 0; i < nindex; i++) {
+        auto ivf = new faiss::IndexIVFFlat(&cd.quantizer, d, nlist);
+        if (i == 0) {
+            auto il = new faiss::OnDiskInvertedLists(
+                    ivf->nlist, ivf->code_size, filename.c_str());
+            ivf->replace_invlists(il, true);
+        }
+        index_shards.add_shard(ivf);
+    }
+
+    EXPECT_TRUE(index_shards.is_trained);
+    index_shards.add_with_ids(nb, cd.database.data(), cd.ids.data());
+    int ndiff = compare_merged(&index_shards, false);
+
+    EXPECT_EQ(ndiff, 0);
+}
+
+// now use ondisk specific merge
+TEST(MERGE, merge_flat_ondisk_2) {
+    faiss::IndexShards index_shards(d, false, false);
+    index_shards.own_indices = true;
+
+    for (int i = 0; i < nindex; i++) {
+        index_shards.add_shard(
+                new faiss::IndexIVFFlat(&cd.quantizer, d, nlist));
+    }
+    EXPECT_TRUE(index_shards.is_trained);
+    index_shards.add_with_ids(nb, cd.database.data(), cd.ids.data());
+    int ndiff = compare_merged(&index_shards, false, false);
+    EXPECT_GE(0, ndiff);
+}
+
+// now use ondisk specific merge and use shift ids
+TEST(MERGE, merge_flat_ondisk_3) {
+    faiss::IndexShards index_shards(d, false, false);
+    index_shards.own_indices = true;
+
+    std::vector<idx_t> ids;
+    for (int i = 0; i < nb; ++i) {
+        int id = i % shard_size;
+        ids.push_back(id);
+    }
+    for (int i = 0; i < nindex; i++) {
+        index_shards.add_shard(
+                new faiss::IndexIVFFlat(&cd.quantizer, d, nlist));
+    }
+    EXPECT_TRUE(index_shards.is_trained);
+    index_shards.add_with_ids(nb, cd.database.data(), ids.data());
+    int ndiff = compare_merged(&index_shards, true, false);
+    EXPECT_GE(0, ndiff);
+}