KnnIndexTester: always emit the number of segments (#132576)

Regardless of force merge or not, it's useful to see the number of segments. Force merge will result in a number of segments of 1, as expected.

Author: ChrisHegarty

qa/vector/src/main/java/org/elasticsearch/test/knn/KnnIndexTester.java

@@ -15,11 +15,14 @@
 import org.apache.lucene.codecs.KnnVectorsFormat;
 import org.apache.lucene.codecs.lucene101.Lucene101Codec;
 import org.apache.lucene.codecs.lucene99.Lucene99HnswVectorsFormat;
+import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.index.IndexReader;
 import org.apache.lucene.index.LogByteSizeMergePolicy;
 import org.apache.lucene.index.LogDocMergePolicy;
 import org.apache.lucene.index.MergePolicy;
 import org.apache.lucene.index.NoMergePolicy;
 import org.apache.lucene.index.TieredMergePolicy;
+import org.apache.lucene.store.FSDirectory;
 import org.elasticsearch.cli.ProcessInfo;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.logging.LogConfigurator;
@@ -37,7 +40,9 @@
 import org.elasticsearch.xcontent.XContentParserConfiguration;
 import org.elasticsearch.xcontent.XContentType;
 
+import java.io.IOException;
 import java.io.InputStream;
+import java.io.UncheckedIOException;
 import java.lang.management.ThreadInfo;
 import java.nio.file.Files;
 import java.nio.file.Path;
@@ -230,10 +235,9 @@ public static void main(String[] args) throws Exception {
                 }
                 if (cmdLineArgs.forceMerge()) {
                     knnIndexer.forceMerge(indexResults);
-                } else {
-                    knnIndexer.numSegments(indexResults);
                 }
             }
+            numSegments(indexPath, indexResults);
             if (cmdLineArgs.queryVectors() != null && cmdLineArgs.numQueries() > 0) {
                 for (int i = 0; i < results.length; i++) {
                     int nProbe = nProbes[i];
@@ -265,6 +269,14 @@ private static MergePolicy getMergePolicy(CmdLineArgs args) {
         return mergePolicy;
     }
 
+    static void numSegments(Path indexPath, KnnIndexTester.Results result) {
+        try (FSDirectory dir = FSDirectory.open(indexPath); IndexReader reader = DirectoryReader.open(dir)) {
+            result.numSegments = reader.leaves().size();
+        } catch (IOException e) {
+            throw new UncheckedIOException("Failed to get segment count for index at " + indexPath, e);
+        }
+    }
+
     static class FormattedResults {
         List<Results> indexResults = new ArrayList<>();
         List<Results> queryResults = new ArrayList<>();

qa/vector/src/main/java/org/elasticsearch/test/knn/KnnIndexer.java

@@ -27,8 +27,6 @@
 import org.apache.lucene.document.KnnFloatVectorField;
 import org.apache.lucene.document.StoredField;
 import org.apache.lucene.index.ConcurrentMergeScheduler;
-import org.apache.lucene.index.DirectoryReader;
-import org.apache.lucene.index.IndexReader;
 import org.apache.lucene.index.IndexWriter;
 import org.apache.lucene.index.IndexWriterConfig;
 import org.apache.lucene.index.MergePolicy;
@@ -94,14 +92,6 @@ class KnnIndexer {
         this.mergePolicy = mergePolicy;
     }
 
-    void numSegments(KnnIndexTester.Results result) {
-        try (FSDirectory dir = FSDirectory.open(indexPath); IndexReader reader = DirectoryReader.open(dir)) {
-            result.numSegments = reader.leaves().size();
-        } catch (IOException e) {
-            throw new UncheckedIOException("Failed to get segment count for index at " + indexPath, e);
-        }
-    }
-
     void createIndex(KnnIndexTester.Results result) throws IOException, InterruptedException, ExecutionException {
         IndexWriterConfig iwc = new IndexWriterConfig().setOpenMode(IndexWriterConfig.OpenMode.CREATE);
         iwc.setCodec(codec);