Add support of multi vector in jni

jni/CMakeLists.txt

@@ -158,9 +158,21 @@ if (${CONFIG_FAISS} STREQUAL ON OR ${CONFIG_ALL} STREQUAL ON OR ${CONFIG_TEST} S
     set(FAISS_ENABLE_PYTHON OFF)
     add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/external/faiss EXCLUDE_FROM_ALL)
 
-    add_library(${TARGET_LIB_FAISS} SHARED ${CMAKE_CURRENT_SOURCE_DIR}/src/org_opensearch_knn_jni_FaissService.cpp ${CMAKE_CURRENT_SOURCE_DIR}/src/faiss_wrapper.cpp)
+    add_library(
+        ${TARGET_LIB_FAISS} SHARED
+        ${CMAKE_CURRENT_SOURCE_DIR}/src/org_opensearch_knn_jni_FaissService.cpp
+        ${CMAKE_CURRENT_SOURCE_DIR}/src/faiss_wrapper.cpp
+        ${CMAKE_CURRENT_SOURCE_DIR}/src/knn_extension/faiss/utils/BitSet.cpp
+        ${CMAKE_CURRENT_SOURCE_DIR}/src/knn_extension/faiss/MultiVectorResultCollector.cpp
+        ${CMAKE_CURRENT_SOURCE_DIR}/src/knn_extension/faiss/MultiVectorResultCollectorFactory.cpp)
     target_link_libraries(${TARGET_LIB_FAISS} faiss ${TARGET_LIB_COMMON} OpenMP::OpenMP_CXX)
-    target_include_directories(${TARGET_LIB_FAISS} PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/include $ENV{JAVA_HOME}/include $ENV{JAVA_HOME}/include/${JVM_OS_TYPE} ${CMAKE_CURRENT_SOURCE_DIR}/external/faiss)
+    target_include_directories(${TARGET_LIB_FAISS} PRIVATE
+        ${CMAKE_CURRENT_SOURCE_DIR}/include
+        ${CMAKE_CURRENT_SOURCE_DIR}/include/knn_extension/faiss
+        ${CMAKE_CURRENT_SOURCE_DIR}/include/knn_extension/faiss/utils
+        $ENV{JAVA_HOME}/include
+        $ENV{JAVA_HOME}/include/${JVM_OS_TYPE}
+        ${CMAKE_CURRENT_SOURCE_DIR}/external/faiss)
     set_target_properties(${TARGET_LIB_FAISS} PROPERTIES SUFFIX ${LIB_EXT})
     set_target_properties(${TARGET_LIB_FAISS} PROPERTIES POSITION_INDEPENDENT_CODE ON)
 
@@ -198,7 +210,12 @@ if ("${WIN32}" STREQUAL "")
                 jni_test
                 tests/faiss_wrapper_test.cpp
                 tests/nmslib_wrapper_test.cpp
-                tests/test_util.cpp)
+                tests/test_util.cpp
+                tests/knn_extension/faiss/utils/BitSetTest.cpp
+                tests/knn_extension/faiss/utils/HeapTest.cpp
+                tests/knn_extension/faiss/MultiVectorResultCollectorTest.cpp
+                tests/knn_extension/faiss/MultiVectorResultCollectorFactoryTest.cpp
+                )
 
         target_link_libraries(
                 jni_test

jni/include/faiss_wrapper.h

@@ -13,7 +13,6 @@
 #define OPENSEARCH_KNN_FAISS_WRAPPER_H
 
 #include "jni_util.h"
-
 #include <jni.h>
 
 namespace knn_jni {
@@ -38,13 +37,13 @@ namespace knn_jni {
         //
         // Return an array of KNNQueryResults
         jobjectArray QueryIndex(knn_jni::JNIUtilInterface * jniUtil, JNIEnv * env, jlong indexPointerJ,
-                                jfloatArray queryVectorJ, jint kJ);
+                                jfloatArray queryVectorJ, jint kJ, jintArray parentIdsJ);
 
         // Execute a query against the index located in memory at indexPointerJ along with Filters
         //
         // Return an array of KNNQueryResults
         jobjectArray QueryIndex_WithFilter(knn_jni::JNIUtilInterface * jniUtil, JNIEnv * env, jlong indexPointerJ,
-                                                                jfloatArray queryVectorJ, jint kJ, jintArray filterIdsJ);
+                                                                jfloatArray queryVectorJ, jint kJ, jintArray filterIdsJ, jintArray parentIdsJ);
 
         // Free the index located in memory at indexPointerJ
         void Free(jlong indexPointer);

jni/include/knn_extension/faiss/MultiVectorResultCollector.h

@@ -0,0 +1,69 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#pragma once
+
+#include <faiss/impl/ResultCollector.h>
+#include <faiss/MetricType.h>
+#include "knn_extension/faiss/utils/BitSet.h"
+#include <unordered_map>
+
+namespace os_faiss {
+
+using idx_t = faiss::idx_t;
+/**
+ * Implementation of ResultCollector to support multi vector
+ *
+ * Only supports HNSW algorithm
+ *
+ * Example:
+ * When there is two lucene document with two nested fields, the parent_bit_set value of 100100 is provided where
+ * parent doc ids are 2, and 5. Doc id for nested fields of parent document 2 are 0, and 1. Doc id for nested fields
+ * of parent document 5 are 3, and 4. For faiss, only nested fields are stored. Therefore corresponding doc ids for
+ * nested fields 0, 1, 3, 4 is 0, 1, 2, 3 in faiss. This mapping data is stored in id_map parameter.
+ *
+ * When collect method is called
+ * 1. It switches from faiss id to lucene id and look for its parent id.
+ * 2. See if the parent id already exist in heap using either parent_id_to_id or parent_id_to_index.
+ * 3. If it does not exist, add the parent id and distance value in the heap(bh_ids, bh_val) and update parent_id_to_id, and parent_id_to_index.
+ * 4. If it does exist, update the distance value(bh_val), parent_id_to_id, and parent_id_to_index.
+ *
+ * When post_process method is called
+ * 1. Convert lucene parent ID to faiss doc ID using parent_id_to_id
+ */
+struct MultiVectorResultCollector:faiss::ResultCollector {
+    // BitSet of lucene parent doc ID
+    const BitSet* parent_bit_set;
+
+    // Mapping data from Faiss doc ID to Lucene doc ID
+    const std::vector<int64_t>* id_map;
+
+    // Lucene parent doc ID to to Faiss doc ID
+    // Lucene parent doc ID to index in heap(bh_val, bh_ids)
+    std::unordered_map<idx_t, idx_t> parent_id_to_id;
+    std::unordered_map<idx_t, size_t> parent_id_to_index;
+    MultiVectorResultCollector(const BitSet* parent_bit_set, const std::vector<int64_t>* id_map);
+
+    /**
+     *
+     * @param k         max size of bh_val, and bh_ids
+     * @param nres      number of results in bh_val, and bh_ids
+     * @param bh_val    binary heap storing values (For this case distance from query to result)
+     * @param bh_ids    binary heap storing document IDs
+     * @param val       a new value to add in bh_val
+     * @param ids       a new doc id to add in bh_ids
+     */
+    void collect(
+            int k,
+            int& nres,
+            float* bh_val,
+            int64_t* bh_ids,
+            float val,
+            int64_t ids) override;
+    void post_process(int64_t nres, int64_t* bh_ids) override;
+};
+
+} // namespace os_faiss
+

jni/include/knn_extension/faiss/MultiVectorResultCollectorFactory.h

@@ -0,0 +1,26 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#pragma once
+
+#include <faiss/impl/ResultCollectorFactory.h>
+#include "knn_extension/faiss/utils/BitSet.h"
+
+namespace os_faiss {
+/**
+ * Create MultiVectorResultCollector for single query request
+ *
+ * Creating new collector is required because MultiVectorResultCollector has instance variables
+ * which should be isolated for each query.
+ */
+struct MultiVectorResultCollectorFactory:faiss::ResultCollectorFactory {
+    BitSet* parent_bit_set;
+
+    MultiVectorResultCollectorFactory(BitSet* parent_bit_set);
+    faiss::ResultCollector* new_collector() override;
+    void delete_collector(faiss::ResultCollector* resultCollector) override;
+};
+
+}  // namespace os_faiss

jni/include/knn_extension/faiss/utils/BitSet.h

@@ -0,0 +1,51 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#pragma once
+
+#include <faiss/MetricType.h>
+#include <faiss/impl/platform_macros.h>
+#include <limits>
+
+using idx_t = faiss::idx_t;
+
+struct BitSet {
+    const int NO_MORE_DOCS = std::numeric_limits<int>::max();
+    /**
+     * Returns the index of the first set bit starting at the index specified.
+     * NO_MORE_DOCS is returned if there are no more set bits.
+     */
+    virtual idx_t next_set_bit(idx_t index) const = 0;
+    virtual ~BitSet() = default;
+};
+
+
+/**
+ * BitSet of fixed length (numBits), implemented using an array of unit64.
+ * See https://github.com/apache/lucene/blob/main/lucene/core/src/java/org/apache/lucene/util/FixedBitSet.java
+ *
+ * Here a block is 64 bit. However, for simplicity let's assume its size is 8 bits.
+ * Then, if have an array of 3, 7, and 10, it will be represented in bitmap as follow.
+ *            [0]      [1]
+ * bitmap: 10001000 00000100
+ *
+ * for next_set_bit call with 4
+ * 1. it looks for bitmap[0]
+ * 2. bitmap[0] >> 4
+ * 3. count trailing zero of the result from step 2 which is 3
+ * 4. return 4(current index) + 3(result from step 3)
+ */
+struct FixedBitSet : public BitSet {
+    // Length of bitmap
+    size_t numBits;
+
+    // Pointer to an array of uint64_t
+    // Using uint64_t to leverage function __builtin_ctzll which is defined in faiss/impl/platform_macros.h
+    uint64_t* bitmap;
+
+    FixedBitSet(const int* int_array, const int length);
+    idx_t next_set_bit(idx_t index) const;
+    ~FixedBitSet();
+};