Use direct IO in tests sometimes

Author: thecoop

server/src/main/java/org/elasticsearch/index/codec/vectors/GenericFlatVectorReaders.java

@@ -18,6 +18,9 @@
 import java.util.IdentityHashMap;
 import java.util.Map;
 
+/**
+ * Keeps track of field-specific raw vector readers for vector reads
+ */
 public class GenericFlatVectorReaders {
 
     public interface Field {
@@ -73,6 +76,7 @@ public Collection<FlatVectorsReader> allReaders() {
     public GenericFlatVectorReaders getMergeInstance() throws IOException {
         GenericFlatVectorReaders mergeReaders = new GenericFlatVectorReaders();
 
+        // link the original instance with the merge instance
         Map<FlatVectorsReader, FlatVectorsReader> mergeInstances = new IdentityHashMap<>();
         for (var reader : readers.entrySet()) {
             FlatVectorsReader mergeInstance = reader.getValue().getMergeInstance();

server/src/main/java/org/elasticsearch/index/codec/vectors/es93/ES93GenericFlatVectorsReader.java

@@ -104,7 +104,6 @@ public FlatVectorsScorer getFlatVectorScorer() {
 
     @Override
     public FlatVectorsReader getMergeInstance() throws IOException {
-        // we know what the reader is, so we can return it directly
         return new ES93GenericFlatVectorsReader(fieldInfos, genericReaders.getMergeInstance());
     }
 

server/src/test/java/org/elasticsearch/index/codec/vectors/es93/ES93BinaryQuantizedVectorsFormatTests.java

@@ -75,11 +75,17 @@ public class ES93BinaryQuantizedVectorsFormatTests extends BaseKnnVectorsFormatT
         LogConfigurator.configureESLogging(); // native access requires logging to be initialized
     }
 
-    static final Codec codec = TestUtil.alwaysKnnVectorsFormat(new ES93BinaryQuantizedVectorsFormat());
+    private KnnVectorsFormat format;
+
+    @Override
+    public void setUp() throws Exception {
+        format = new ES93BinaryQuantizedVectorsFormat(random().nextBoolean());
+        super.setUp();
+    }
 
     @Override
     protected Codec getCodec() {
-        return codec;
+        return TestUtil.alwaysKnnVectorsFormat(format);
     }
 
     @Override
@@ -118,7 +124,7 @@ public void testEmptyDiversifiedChildSearch() throws Exception {
         float[] vector = randomVector(dims);
         VectorSimilarityFunction similarityFunction = VectorSimilarityFunction.EUCLIDEAN;
         try (Directory d = newDirectory()) {
-            IndexWriterConfig iwc = newIndexWriterConfig().setCodec(codec);
+            IndexWriterConfig iwc = newIndexWriterConfig().setCodec(getCodec());
             iwc.setMergePolicy(new SoftDeletesRetentionMergePolicy("soft_delete", MatchAllDocsQuery::new, iwc.getMergePolicy()));
             try (IndexWriter w = new IndexWriter(d, iwc)) {
                 List<Document> toAdd = new ArrayList<>();