Adding logs for getting the times

Signed-off-by: Navneet Verma <navneev@amazon.com>

src/main/java/org/opensearch/knn/index/codec/KNN990Codec/NativeEngines990KnnVectorsWriter.java

@@ -105,13 +105,16 @@ public void flush(int maxDoc, final Sorter.DocMap sortMap) throws IOException {
     @Override
     public void mergeOneField(final FieldInfo fieldInfo, final MergeState mergeState) throws IOException {
         // This will ensure that we are merging the FlatIndex during force merge.
+        StopWatch stopwatch = new StopWatch().start();
         flatVectorsWriter.mergeOneField(fieldInfo, mergeState);
-
+        log.info("Merge : Reading and writing merged FlatVector Took : {} ms", stopwatch.stop().totalTime().millis());
         final VectorDataType vectorDataType = extractVectorDataType(fieldInfo);
         final Supplier<KNNVectorValues<?>> knnVectorValuesSupplier = () -> getVectorValues(vectorDataType, fieldInfo, mergeState);
+        stopwatch = new StopWatch().start();
         final QuantizationState quantizationState = train(fieldInfo, knnVectorValuesSupplier);
         final KNNVectorValues<?> knnVectorValues = knnVectorValuesSupplier.get();
         final int totalLiveDocs = Math.toIntExact(knnVectorValues.totalLiveDocs());
+        log.info("Merge : Reading new live docs Took with merging vector values : {} ms", stopwatch.stop().totalTime().millis());
         if (totalLiveDocs <= 0) {
             log.debug("[Merge] No live docs for field {}", fieldInfo.getName());
             return;