Update default to 0 to always build graph as default behavior

Signed-off-by: Balasubramanian <[email protected]>

CHANGELOG.md

@@ -30,6 +30,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Make the build work for M series MacOS without manual code changes and local JAVA_HOME config (#2397)[https://github.com/opensearch-project/k-NN/pull/2397]
 - Remove DocsWithFieldSet reference from NativeEngineFieldVectorsWriter (#2408)[https://github.com/opensearch-project/k-NN/pull/2408]
 - Remove skip building graph check for quantization use case (#2430)[https://github.com/opensearch-project/k-NN/2430]
+- Update default to 0 to always build graph as default behavior (#52)[https://github.com/opensearch-project/k-NN/pull/2452]
 ### Bug Fixes
 * Fixing the bug when a segment has no vector field present for disk based vector search (#2282)[https://github.com/opensearch-project/k-NN/pull/2282]
 * Fixing the bug where search fails with "fields" parameter for an index with a knn_vector field (#2314)[https://github.com/opensearch-project/k-NN/pull/2314]

src/main/java/org/opensearch/knn/index/KNNSettings.java

@@ -101,7 +101,7 @@ public class KNNSettings {
     public static final boolean KNN_DEFAULT_FAISS_AVX512_DISABLED_VALUE = false;
     public static final boolean KNN_DEFAULT_FAISS_AVX512_SPR_DISABLED_VALUE = false;
     public static final String INDEX_KNN_DEFAULT_SPACE_TYPE = "l2";
-    public static final Integer INDEX_KNN_ADVANCED_APPROXIMATE_THRESHOLD_DEFAULT_VALUE = 15_000;
+    public static final Integer INDEX_KNN_ADVANCED_APPROXIMATE_THRESHOLD_DEFAULT_VALUE = 0;
     public static final Integer INDEX_KNN_BUILD_VECTOR_DATA_STRUCTURE_THRESHOLD_MIN = -1;
     public static final Integer INDEX_KNN_BUILD_VECTOR_DATA_STRUCTURE_THRESHOLD_MAX = Integer.MAX_VALUE - 2;
     public static final String INDEX_KNN_DEFAULT_SPACE_TYPE_FOR_BINARY = "hamming";