Deprecate nmslib engine

CHANGELOG.md

@@ -57,4 +57,5 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 * Bump Faiss commit from 1f42e81 to 0cbc2a8 to accelerate hamming distance calculation using _mm512_popcnt_epi64  intrinsic and also add avx512-fp16 instructions to boost performance [#2381](https://github.com/opensearch-project/k-NN/pull/2381)
 * Enabled indices.breaker.total.use_real_memory setting via build.gradle for integTest Cluster to catch heap CB in local ITs and github CI actions [#2395](https://github.com/opensearch-project/k-NN/pull/2395/) 
 * Fixing Lucene912Codec Issue with BWC for Lucene 10.0.1 upgrade[#2429](https://github.com/opensearch-project/k-NN/pull/2429)
+* Deprecate nmslib engine (#2427)[https://github.com/opensearch-project/k-NN/pull/2427]
 ### Refactoring

src/main/java/org/opensearch/knn/common/KNNConstants.java

@@ -91,6 +91,7 @@ public class KNNConstants {
     public static final int LUCENE_SQ_DEFAULT_BITS = 7;
 
     // nmslib specific constants
+    @Deprecated(since = "2.19.0", forRemoval = true)
     public static final String NMSLIB_NAME = "nmslib";
     public static final String COMMONS_NAME = "common";
     public static final String SPACE_TYPE = "spaceType"; // used as field info key

src/main/java/org/opensearch/knn/index/engine/EngineResolver.java

@@ -5,14 +5,19 @@
 
 package org.opensearch.knn.index.engine;
 
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
 import org.opensearch.knn.index.mapper.CompressionLevel;
 import org.opensearch.knn.index.mapper.Mode;
 
+import static org.opensearch.knn.index.engine.KNNEngine.DEPRECATED_ENGINES;
+
 /**
  * Figures out what {@link KNNEngine} to use based on configuration details
  */
 public final class EngineResolver {
 
+    private static Logger logger = LogManager.getLogger(EngineResolver.class);
     public static final EngineResolver INSTANCE = new EngineResolver();
 
     private EngineResolver() {}
@@ -32,31 +37,38 @@ public KNNEngine resolveEngine(
     ) {
         // User configuration gets precedence
         if (knnMethodContext != null && knnMethodContext.isEngineConfigured()) {
-            return knnMethodContext.getKnnEngine();
+            return logAndReturnEngine(knnMethodContext.getKnnEngine());
         }
 
         // Faiss is the only engine that supports training, so we default to faiss here for now
         if (requiresTraining) {
-            return KNNEngine.FAISS;
+            return logAndReturnEngine(KNNEngine.FAISS);
         }
 
         Mode mode = knnMethodConfigContext.getMode();
         CompressionLevel compressionLevel = knnMethodConfigContext.getCompressionLevel();
         // If both mode and compression are not specified, we can just default
         if (Mode.isConfigured(mode) == false && CompressionLevel.isConfigured(compressionLevel) == false) {
-            return KNNEngine.DEFAULT;
+            return logAndReturnEngine(KNNEngine.DEFAULT);
         }
 
         // For 1x, we need to default to faiss if mode is provided and use nmslib otherwise
         if (CompressionLevel.isConfigured(compressionLevel) == false || compressionLevel == CompressionLevel.x1) {
-            return mode == Mode.ON_DISK ? KNNEngine.FAISS : KNNEngine.NMSLIB;
+            return logAndReturnEngine(mode == Mode.ON_DISK ? KNNEngine.FAISS : KNNEngine.NMSLIB);
         }
 
         // Lucene is only engine that supports 4x - so we have to default to it here.
         if (compressionLevel == CompressionLevel.x4) {
-            return KNNEngine.LUCENE;
+            return logAndReturnEngine(KNNEngine.LUCENE);
         }
 
-        return KNNEngine.FAISS;
+        return logAndReturnEngine(KNNEngine.FAISS);
+    }
+
+    private KNNEngine logAndReturnEngine(KNNEngine knnEngine) {
+        if (DEPRECATED_ENGINES.contains(knnEngine)) {
+            logger.warn("[Deprecation] {} engine is deprecated and will be removed in a future release.", knnEngine);
+        }
+        return knnEngine;
     }
 }

src/main/java/org/opensearch/knn/index/engine/KNNEngine.java

@@ -25,6 +25,7 @@
  * passed to the respective k-NN library's JNI layer.
  */
 public enum KNNEngine implements KNNLibrary {
+    @Deprecated(since = "2.19.0", forRemoval = true)
     NMSLIB(NMSLIB_NAME, Nmslib.INSTANCE),
     FAISS(FAISS_NAME, Faiss.INSTANCE),
     LUCENE(LUCENE_NAME, Lucene.INSTANCE);
@@ -34,6 +35,7 @@ public enum KNNEngine implements KNNLibrary {
     private static final Set<KNNEngine> CUSTOM_SEGMENT_FILE_ENGINES = ImmutableSet.of(KNNEngine.NMSLIB, KNNEngine.FAISS);
     private static final Set<KNNEngine> ENGINES_SUPPORTING_FILTERS = ImmutableSet.of(KNNEngine.LUCENE, KNNEngine.FAISS);
     public static final Set<KNNEngine> ENGINES_SUPPORTING_RADIAL_SEARCH = ImmutableSet.of(KNNEngine.LUCENE, KNNEngine.FAISS);
+    public static final Set<KNNEngine> DEPRECATED_ENGINES = ImmutableSet.of(KNNEngine.NMSLIB);
 
     private static Map<KNNEngine, Integer> MAX_DIMENSIONS_BY_ENGINE = Map.of(
         KNNEngine.NMSLIB,

src/main/java/org/opensearch/knn/index/engine/nmslib/Nmslib.java

@@ -22,7 +22,11 @@
 
 /**
  * Implements NativeLibrary for the nmslib native library
+ *
+ * @deprecated As of 2.19.0, please use {@link org.opensearch.knn.index.engine.faiss.Faiss} or Lucene's native k-NN.
+ * This engine will be removed in a future release.
  */
+@Deprecated(since = "2.19.0", forRemoval = true)
 public class Nmslib extends NativeLibrary {
     // Extension to be used for Nmslib files. It is ".hnsw" and not ".nmslib" for legacy purposes.
     public final static String EXTENSION = ".hnsw";

src/main/java/org/opensearch/knn/index/engine/nmslib/NmslibHNSWMethod.java

@@ -24,7 +24,11 @@
 
 /**
  * Nmslib's HNSW implementation
+ *
+ * @deprecated As of 2.19.0, please use {@link org.opensearch.knn.index.engine.faiss.Faiss} or Lucene engine.
+ * This engine will be removed in a future release.
  */
+@Deprecated(since = "2.19.0", forRemoval = true)
 public class NmslibHNSWMethod extends AbstractKNNMethod {
 
     private static final Set<VectorDataType> SUPPORTED_DATA_TYPES = ImmutableSet.of(VectorDataType.FLOAT);

src/main/java/org/opensearch/knn/index/engine/nmslib/NmslibMethodResolver.java

@@ -23,7 +23,11 @@
 /**
  * Method resolution logic for nmslib. Because nmslib does not support quantization, it is in general a validation
  * before returning the original request
+ *
+ * @deprecated As of 2.19.0, please use {@link org.opensearch.knn.index.engine.faiss.Faiss} or Lucene engine.
+ * This engine will be removed in a future release.
  */
+@Deprecated(since = "2.19.0", forRemoval = true)
 public class NmslibMethodResolver extends AbstractMethodResolver {
 
     private static final Set<CompressionLevel> SUPPORTED_COMPRESSION_LEVELS = Set.of(CompressionLevel.x1);

src/main/java/org/opensearch/knn/jni/JNIService.java

@@ -27,6 +27,7 @@
  * Service to distribute requests to the proper engine jni service
  */
 public class JNIService {
+
     /**
      * Initialize an index for the native library. Takes in numDocs to
      * allocate the correct amount of memory.

src/main/java/org/opensearch/knn/jni/NmslibService.java

@@ -28,7 +28,11 @@
  * javac -h jni/include src/main/java/org/opensearch/knn/jni/NmslibService.java
  *      src/main/java/org/opensearch/knn/index/KNNQueryResult.java
  *      src/main/java/org/opensearch/knn/common/KNNConstants.java
+ *
+ *  @deprecated As of 2.19.0, please use {@link FaissService} or Lucene.
+ *  This engine will be removed in a future release.
  */
+@Deprecated(since = "2.19.0", forRemoval = true)
 class NmslibService {
 
     static {

src/test/java/org/opensearch/knn/index/NmslibIT.java

@@ -38,6 +38,7 @@
 import static org.hamcrest.Matchers.containsString;
 import static org.opensearch.knn.common.KNNConstants.KNN_ENGINE;
 
+@Deprecated(since = "2.19.0", forRemoval = true)
 public class NmslibIT extends KNNRestTestCase {
 
     static TestUtils.TestData testData;

src/test/java/org/opensearch/knn/index/engine/nmslib/NmslibMethodResolverTests.java

@@ -23,6 +23,7 @@
 
 import static org.opensearch.knn.common.KNNConstants.METHOD_HNSW;
 
+@Deprecated(since = "2.19.0", forRemoval = true)
 public class NmslibMethodResolverTests extends KNNTestCase {
 
     MethodResolver TEST_RESOLVER = new NmslibMethodResolver();