Use dafault BM25Similarity

Signed-off-by: Prudhvi Godithi <pgodithi@amazon.com>

Author: prudhvigodithi

modules/parent-join/src/yamlRestTest/resources/rest-api-spec/test/30_inner_hits.yml

@@ -79,11 +79,11 @@ teardown:
 
 
     - match: { hits.total.value: 2 }
-    - match: { hits.hits.0._id: "3" }
-    - match: { hits.hits.0.inner_hits.question.hits.total.value: 0}
-    - match: { hits.hits.1._id: "2" }
-    - match: { hits.hits.1.inner_hits.question.hits.total.value: 1}
-    - match: { hits.hits.1.inner_hits.question.hits.hits.0._id: "1"}
+    - match: { hits.hits.0._id: "2" }
+    - match: { hits.hits.0.inner_hits.question.hits.total.value: 1 }
+    - match: { hits.hits.0.inner_hits.question.hits.hits.0._id: "1" }
+    - match: { hits.hits.1._id: "3" }
+    - match: { hits.hits.1.inner_hits.question.hits.total.value: 0 }
 
 ---
 "HasParent disallow expensive queries":

modules/parent-join/src/yamlRestTest/resources/rest-api-spec/test/50_legacy_bm25.yml

@@ -0,0 +1,44 @@
+---
+setup:
+  - do:
+      indices.create:
+        index: legacy_bm25_test
+        body:
+          settings:
+            number_of_shards: 1
+            number_of_replicas: 0
+            similarity:
+              default:
+                type: LegacyBM25
+                k1: 1.2
+                b: 0.75
+          mappings:
+            properties:
+              content:
+                type: text
+  - do:
+      index:
+        index: legacy_bm25_test
+        id: "1"
+        body: { "content": "This is a test document for legacy BM25 scoring" }
+  - do:
+      indices.refresh:
+        index: legacy_bm25_test
+
+---
+"Legacy BM25 search":
+  - do:
+      search:
+        index: legacy_bm25_test
+        body:
+          query:
+            match:
+              content: "legacy"
+  - match: { hits.total.value: 1 }
+  - match: { hits.hits.0._id: "1" }
+
+---
+teardown:
+  - do:
+      indices.delete:
+        index: legacy_bm25_test

server/src/main/java/org/opensearch/index/similarity/SimilarityProviders.java

@@ -35,6 +35,7 @@
 import org.apache.lucene.search.similarities.AfterEffect;
 import org.apache.lucene.search.similarities.AfterEffectB;
 import org.apache.lucene.search.similarities.AfterEffectL;
+import org.apache.lucene.search.similarities.BM25Similarity;
 import org.apache.lucene.search.similarities.BasicModel;
 import org.apache.lucene.search.similarities.BasicModelG;
 import org.apache.lucene.search.similarities.BasicModelIF;
@@ -62,6 +63,7 @@
 import org.apache.lucene.search.similarities.NormalizationH2;
 import org.apache.lucene.search.similarities.NormalizationH3;
 import org.apache.lucene.search.similarities.NormalizationZ;
+import org.apache.lucene.search.similarities.Similarity;
 import org.opensearch.Version;
 import org.opensearch.common.logging.DeprecationLogger;
 import org.opensearch.common.settings.Settings;
@@ -271,13 +273,21 @@ static void assertSettingsIsSubsetOf(String type, Version version, Settings sett
         }
     }
 
-    public static LegacyBM25Similarity createBM25Similarity(Settings settings, Version indexCreatedVersion) {
+    public static Similarity createBM25Similarity(Settings settings, Version indexCreatedVersion) {
         assertSettingsIsSubsetOf("BM25", indexCreatedVersion, settings, "k1", "b", DISCOUNT_OVERLAPS);
 
         float k1 = settings.getAsFloat("k1", 1.2f);
         float b = settings.getAsFloat("b", 0.75f);
         boolean discountOverlaps = settings.getAsBoolean(DISCOUNT_OVERLAPS, true);
 
+        return new BM25Similarity(k1, b, discountOverlaps);
+    }
+
+    public static Similarity createLegacyBM25Similarity(Settings settings, Version indexCreatedVersion) {
+        assertSettingsIsSubsetOf("LegacyBM25", indexCreatedVersion, settings, "k1", "b", DISCOUNT_OVERLAPS);
+        float k1 = settings.getAsFloat("k1", 1.2f);
+        float b = settings.getAsFloat("b", 0.75f);
+        boolean discountOverlaps = settings.getAsBoolean(DISCOUNT_OVERLAPS, true);
         return new LegacyBM25Similarity(k1, b, discountOverlaps);
     }
 

server/src/main/java/org/opensearch/index/similarity/SimilarityService.java

@@ -37,6 +37,7 @@
 import org.apache.lucene.search.CollectionStatistics;
 import org.apache.lucene.search.Explanation;
 import org.apache.lucene.search.TermStatistics;
+import org.apache.lucene.search.similarities.BM25Similarity;
 import org.apache.lucene.search.similarities.BooleanSimilarity;
 import org.apache.lucene.search.similarities.PerFieldSimilarityWrapper;
 import org.apache.lucene.search.similarities.Similarity;
@@ -52,7 +53,6 @@
 import org.opensearch.index.IndexSettings;
 import org.opensearch.index.mapper.MappedFieldType;
 import org.opensearch.index.mapper.MapperService;
-import org.opensearch.lucene.similarity.LegacyBM25Similarity;
 import org.opensearch.script.ScriptService;
 
 import java.util.Collections;
@@ -84,7 +84,7 @@ public final class SimilarityService extends AbstractIndexComponent {
             };
         });
         defaults.put("BM25", version -> {
-            final LegacyBM25Similarity similarity = SimilarityProviders.createBM25Similarity(Settings.EMPTY, version);
+            final Similarity similarity = new BM25Similarity();
             return () -> similarity;
         });
         defaults.put("boolean", version -> {
@@ -100,6 +100,7 @@ public final class SimilarityService extends AbstractIndexComponent {
             );
         });
         builtIn.put("BM25", (settings, version, scriptService) -> SimilarityProviders.createBM25Similarity(settings, version));
+        builtIn.put("LegacyBM25", (settings, version, scriptService) -> SimilarityProviders.createLegacyBM25Similarity(settings, version));
         builtIn.put("boolean", (settings, version, scriptService) -> SimilarityProviders.createBooleanSimilarity(settings, version));
         builtIn.put("DFR", (settings, version, scriptService) -> SimilarityProviders.createDfrSimilarity(settings, version));
         builtIn.put("IB", (settings, version, scriptService) -> SimilarityProviders.createIBSimilarity(settings, version));

server/src/test/java/org/opensearch/index/similarity/SimilarityServiceTests.java

@@ -34,6 +34,7 @@
 import org.apache.lucene.index.FieldInvertState;
 import org.apache.lucene.search.CollectionStatistics;
 import org.apache.lucene.search.TermStatistics;
+import org.apache.lucene.search.similarities.BM25Similarity;
 import org.apache.lucene.search.similarities.BooleanSimilarity;
 import org.apache.lucene.search.similarities.Similarity;
 import org.opensearch.Version;
@@ -53,6 +54,13 @@ public void testDefaultSimilarity() {
         Settings settings = Settings.builder().build();
         IndexSettings indexSettings = IndexSettingsModule.newIndexSettings("test", settings);
         SimilarityService service = new SimilarityService(indexSettings, null, Collections.emptyMap());
+        assertThat(service.getDefaultSimilarity(), instanceOf(BM25Similarity.class));
+    }
+
+    public void testLegacySimilarity() {
+        Settings settings = Settings.builder().put("index.similarity.default.type", "LegacyBM25").build();
+        IndexSettings indexSettings = IndexSettingsModule.newIndexSettings("test", settings);
+        SimilarityService service = new SimilarityService(indexSettings, null, Collections.emptyMap());
         assertThat(service.getDefaultSimilarity(), instanceOf(LegacyBM25Similarity.class));
     }
 

server/src/test/java/org/opensearch/index/similarity/SimilarityTests.java

@@ -33,6 +33,7 @@
 package org.opensearch.index.similarity;
 
 import org.apache.lucene.search.similarities.AfterEffectL;
+import org.apache.lucene.search.similarities.BM25Similarity;
 import org.apache.lucene.search.similarities.BasicModelG;
 import org.apache.lucene.search.similarities.BooleanSimilarity;
 import org.apache.lucene.search.similarities.DFISimilarity;
@@ -72,7 +73,7 @@ protected Collection<Class<? extends Plugin>> getPlugins() {
 
     public void testResolveDefaultSimilarities() {
         SimilarityService similarityService = createIndex("foo").similarityService();
-        assertThat(similarityService.getSimilarity("BM25").get(), instanceOf(LegacyBM25Similarity.class));
+        assertThat(similarityService.getSimilarity("BM25").get(), instanceOf(BM25Similarity.class));
         assertThat(similarityService.getSimilarity("boolean").get(), instanceOf(BooleanSimilarity.class));
         assertThat(similarityService.getSimilarity("default"), equalTo(null));
         IllegalArgumentException e = expectThrows(IllegalArgumentException.class, () -> similarityService.getSimilarity("classic"));
@@ -83,7 +84,29 @@ public void testResolveDefaultSimilarities() {
         );
     }
 
-    public void testResolveSimilaritiesFromMapping_classicIsForbidden() throws IOException {
+    public void testResolveLegacySimilarity() throws IOException {
+        Settings settings = Settings.builder()
+            .put("index.similarity.my_similarity.type", "LegacyBM25")
+            .put("index.similarity.my_similarity.k1", 1.2f)
+            .put("index.similarity.my_similarity.b", 0.75f)
+            .put("index.similarity.my_similarity.discount_overlaps", false)
+            .build();
+
+        XContentBuilder mapping = XContentFactory.jsonBuilder()
+            .startObject()
+            .startObject("properties")
+            .startObject("dummy")
+            .field("type", "text")
+            .field("similarity", "my_similarity")
+            .endObject()
+            .endObject()
+            .endObject();
+
+        MapperService mapperService = createIndex("foo", settings, "type", mapping).mapperService();
+        assertThat(mapperService.fieldType("dummy").getTextSearchInfo().getSimilarity().get(), instanceOf(LegacyBM25Similarity.class));
+    }
+
+    public void testResolveSimilaritiesFromMapping_classicIsForbidden() {
         Settings indexSettings = Settings.builder()
             .put("index.similarity.my_similarity.type", "classic")
             .put("index.similarity.my_similarity.discount_overlaps", false)
@@ -114,9 +137,12 @@ public void testResolveSimilaritiesFromMapping_bm25() throws IOException {
             .put("index.similarity.my_similarity.discount_overlaps", false)
             .build();
         MapperService mapperService = createIndex("foo", indexSettings, "type", mapping).mapperService();
-        assertThat(mapperService.fieldType("field1").getTextSearchInfo().getSimilarity().get(), instanceOf(LegacyBM25Similarity.class));
+        assertThat(
+            mapperService.fieldType("field1").getTextSearchInfo().getSimilarity().get(),
+            instanceOf(BM25Similarity.class)
+        );
 
-        LegacyBM25Similarity similarity = (LegacyBM25Similarity) mapperService.fieldType("field1")
+        BM25Similarity similarity = (BM25Similarity) mapperService.fieldType("field1")
             .getTextSearchInfo()
             .getSimilarity()
             .get();