diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index c11c775..2d98bc5 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -208,10 +208,6 @@
 
 * GITHUB#13156: Hunspell: don't proceed with other suggestions if we found good REP ones (Peter Gromov)
 
-* GITHUB#13124: MergeScheduler can now provide an executor for intra-merge parallelism. The first
-  implementation is the ConcurrentMergeScheduler and the Lucene99HnswVectorsFormat will use it if no other
-  executor is provided. (Ben Trent)
-
 Optimizations
 ---------------------
 
diff --git a/lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99HnswVectorsFormat.java b/lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99HnswVectorsFormat.java
index bcea401..582155d 100644
--- a/lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99HnswVectorsFormat.java
+++ b/lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99HnswVectorsFormat.java
@@ -24,8 +24,6 @@
 import org.apache.lucene.codecs.KnnVectorsReader;
 import org.apache.lucene.codecs.KnnVectorsWriter;
 import org.apache.lucene.codecs.lucene90.IndexedDISI;
-import org.apache.lucene.index.MergePolicy;
-import org.apache.lucene.index.MergeScheduler;
 import org.apache.lucene.index.SegmentReadState;
 import org.apache.lucene.index.SegmentWriteState;
 import org.apache.lucene.search.DocIdSetIterator;
@@ -165,8 +163,7 @@
    * @param numMergeWorkers number of workers (threads) that will be used when doing merge. If
    *     larger than 1, a non-null {@link ExecutorService} must be passed as mergeExec
    * @param mergeExec the {@link ExecutorService} that will be used by ALL vector writers that are
-   *     generated by this format to do the merge. If null, the configured {@link
-   *     MergeScheduler#getIntraMergeExecutor(MergePolicy.OneMerge)} is used.
+   *     generated by this format to do the merge
    */
   public Lucene99HnswVectorsFormat(
       int maxConn, int beamWidth, int numMergeWorkers, ExecutorService mergeExec) {
@@ -187,6 +184,10 @@
     }
     this.maxConn = maxConn;
     this.beamWidth = beamWidth;
+    if (numMergeWorkers > 1 && mergeExec == null) {
+      throw new IllegalArgumentException(
+          "No executor service passed in when " + numMergeWorkers + " merge workers are requested");
+    }
     if (numMergeWorkers == 1 && mergeExec != null) {
       throw new IllegalArgumentException(
           "No executor service is needed as we'll use single thread to merge");
diff --git a/lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99HnswVectorsWriter.java b/lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99HnswVectorsWriter.java
index 1bd2c53..a236dd7 100644
--- a/lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99HnswVectorsWriter.java
+++ b/lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99HnswVectorsWriter.java
@@ -352,14 +352,7 @@
       int[][] vectorIndexNodeOffsets = null;
       if (scorerSupplier.totalVectorCount() > 0) {
         // build graph
-        HnswGraphMerger merger =
-            createGraphMerger(
-                fieldInfo,
-                scorerSupplier,
-                mergeState.intraMergeTaskExecutor == null
-                    ? null
-                    : new TaskExecutor(mergeState.intraMergeTaskExecutor),
-                numMergeWorkers);
+        HnswGraphMerger merger = createGraphMerger(fieldInfo, scorerSupplier);
         for (int i = 0; i < mergeState.liveDocs.length; i++) {
           merger.addReader(
               mergeState.knnVectorsReaders[i], mergeState.docMaps[i], mergeState.liveDocs[i]);
@@ -496,23 +489,11 @@
   }
 
   private HnswGraphMerger createGraphMerger(
-      FieldInfo fieldInfo,
-      RandomVectorScorerSupplier scorerSupplier,
-      TaskExecutor parallelMergeTaskExecutor,
-      int numParallelMergeWorkers) {
+      FieldInfo fieldInfo, RandomVectorScorerSupplier scorerSupplier) {
     if (mergeExec != null) {
       return new ConcurrentHnswMerger(
           fieldInfo, scorerSupplier, M, beamWidth, mergeExec, numMergeWorkers);
     }
-    if (parallelMergeTaskExecutor != null) {
-      return new ConcurrentHnswMerger(
-          fieldInfo,
-          scorerSupplier,
-          M,
-          beamWidth,
-          parallelMergeTaskExecutor,
-          numParallelMergeWorkers);
-    }
     return new IncrementalHnswGraphMerger(fieldInfo, scorerSupplier, M, beamWidth);
   }
 
diff --git a/lucene/core/src/java/org/apache/lucene/index/ConcurrentMergeScheduler.java b/lucene/core/src/java/org/apache/lucene/index/ConcurrentMergeScheduler.java
index 25b489a..8ffbbd7 100644
--- a/lucene/core/src/java/org/apache/lucene/index/ConcurrentMergeScheduler.java
+++ b/lucene/core/src/java/org/apache/lucene/index/ConcurrentMergeScheduler.java
@@ -21,12 +21,9 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Locale;
-import java.util.concurrent.Executor;
-import java.util.concurrent.SynchronousQueue;
-import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
-import java.util.concurrent.atomic.AtomicInteger;
 import org.apache.lucene.index.MergePolicy.OneMerge;
+import org.apache.lucene.internal.tests.ConcurrentMergeSchedulerAccess;
 import org.apache.lucene.internal.tests.TestSecrets;
 import org.apache.lucene.store.AlreadyClosedException;
 import org.apache.lucene.store.Directory;
@@ -112,9 +109,6 @@
 
   private double forceMergeMBPerSec = Double.POSITIVE_INFINITY;
 
-  /** The executor provided for intra-merge parallelization */
-  protected CachedExecutor intraMergeExecutor;
-
   /** Sole constructor, with all settings set to default values. */
   public ConcurrentMergeScheduler() {}
 
@@ -266,16 +260,6 @@
   }
 
   @Override
-  public Executor getIntraMergeExecutor(OneMerge merge) {
-    assert intraMergeExecutor != null : "scaledExecutor is not initialized";
-    // don't do multithreaded merges for small merges
-    if (merge.estimatedMergeBytes < MIN_BIG_MERGE_MB * 1024 * 1024) {
-      return super.getIntraMergeExecutor(merge);
-    }
-    return intraMergeExecutor;
-  }
-
-  @Override
   public Directory wrapForMerge(OneMerge merge, Directory in) {
     Thread mergeThread = Thread.currentThread();
     if (!MergeThread.class.isInstance(mergeThread)) {
@@ -462,13 +446,7 @@
 
   @Override
   public void close() {
-    try {
-      sync();
-    } finally {
-      if (intraMergeExecutor != null) {
-        intraMergeExecutor.shutdown();
-      }
-    }
+    sync();
   }
 
   /**
@@ -532,9 +510,6 @@
   void initialize(InfoStream infoStream, Directory directory) throws IOException {
     super.initialize(infoStream, directory);
     initDynamicDefaults(directory);
-    if (intraMergeExecutor == null) {
-      intraMergeExecutor = new CachedExecutor();
-    }
   }
 
   @Override
@@ -780,16 +755,11 @@
 
   @Override
   public String toString() {
-    return getClass().getSimpleName()
-        + ": "
-        + "maxThreadCount="
-        + maxThreadCount
-        + ", "
-        + "maxMergeCount="
-        + maxMergeCount
-        + ", "
-        + "ioThrottle="
-        + doAutoIOThrottle;
+    StringBuilder sb = new StringBuilder(getClass().getSimpleName() + ": ");
+    sb.append("maxThreadCount=").append(maxThreadCount).append(", ");
+    sb.append("maxMergeCount=").append(maxMergeCount).append(", ");
+    sb.append("ioThrottle=").append(doAutoIOThrottle);
+    return sb.toString();
   }
 
   private boolean isBacklog(long now, OneMerge merge) {
@@ -932,58 +902,12 @@
   }
 
   static {
-    TestSecrets.setConcurrentMergeSchedulerAccess(ConcurrentMergeScheduler::setSuppressExceptions);
-  }
-
-  /**
-   * This executor provides intra-merge threads for parallel execution of merge tasks. It provides a
-   * limited number of threads to execute merge tasks. In particular, if the number of
-   * `mergeThreads` is equal to `maxThreadCount`, then the executor will execute the merge task in
-   * the calling thread.
-   */
-  private class CachedExecutor implements Executor {
-
-    private final AtomicInteger activeCount = new AtomicInteger(0);
-    private final ThreadPoolExecutor executor;
-
-    public CachedExecutor() {
-      this.executor =
-          new ThreadPoolExecutor(0, 1024, 1L, TimeUnit.MINUTES, new SynchronousQueue<>());
-    }
-
-    void shutdown() {
-      executor.shutdown();
-    }
-
-    @Override
-    public void execute(Runnable command) {
-      final boolean isThreadAvailable;
-      // we need to check if a thread is available before submitting the task to the executor
-      // synchronize on CMS to get an accurate count of current threads
-      synchronized (ConcurrentMergeScheduler.this) {
-        int max = maxThreadCount - mergeThreads.size() - 1;
-        int value = activeCount.get();
-        if (value < max) {
-          activeCount.incrementAndGet();
-          assert activeCount.get() > 0 : "active count must be greater than 0 after increment";
-          isThreadAvailable = true;
-        } else {
-          isThreadAvailable = false;
-        }
-      }
-      if (isThreadAvailable) {
-        executor.execute(
-            () -> {
-              try {
-                command.run();
-              } finally {
-                activeCount.decrementAndGet();
-                assert activeCount.get() >= 0 : "unexpected negative active count";
-              }
-            });
-      } else {
-        command.run();
-      }
-    }
+    TestSecrets.setConcurrentMergeSchedulerAccess(
+        new ConcurrentMergeSchedulerAccess() {
+          @Override
+          public void setSuppressExceptions(ConcurrentMergeScheduler cms) {
+            cms.setSuppressExceptions();
+          }
+        });
   }
 }
diff --git a/lucene/core/src/java/org/apache/lucene/index/IndexWriter.java b/lucene/core/src/java/org/apache/lucene/index/IndexWriter.java
index 6797a74..c81abc3 100644
--- a/lucene/core/src/java/org/apache/lucene/index/IndexWriter.java
+++ b/lucene/core/src/java/org/apache/lucene/index/IndexWriter.java
@@ -3430,14 +3430,7 @@
     }
 
     SegmentMerger merger =
-        new SegmentMerger(
-            readers,
-            segInfo,
-            infoStream,
-            trackingDir,
-            globalFieldNumberMap,
-            context,
-            mergeScheduler.getIntraMergeExecutor(merge));
+        new SegmentMerger(readers, segInfo, infoStream, trackingDir, globalFieldNumberMap, context);
 
     if (!merger.shouldMerge()) {
       return;
@@ -5226,13 +5219,7 @@
 
       final SegmentMerger merger =
           new SegmentMerger(
-              mergeReaders,
-              merge.info.info,
-              infoStream,
-              dirWrapper,
-              globalFieldNumberMap,
-              context,
-              mergeScheduler.getIntraMergeExecutor(merge));
+              mergeReaders, merge.info.info, infoStream, dirWrapper, globalFieldNumberMap, context);
       merge.info.setSoftDelCount(Math.toIntExact(softDeleteCount.get()));
       merge.checkAborted();
 
diff --git a/lucene/core/src/java/org/apache/lucene/index/MergeScheduler.java b/lucene/core/src/java/org/apache/lucene/index/MergeScheduler.java
index b6cfe73..1017204 100644
--- a/lucene/core/src/java/org/apache/lucene/index/MergeScheduler.java
+++ b/lucene/core/src/java/org/apache/lucene/index/MergeScheduler.java
@@ -18,12 +18,10 @@
 
 import java.io.Closeable;
 import java.io.IOException;
-import java.util.concurrent.Executor;
 import org.apache.lucene.index.MergePolicy.OneMerge;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.store.RateLimitedIndexOutput;
 import org.apache.lucene.util.InfoStream;
-import org.apache.lucene.util.SameThreadExecutorService;
 
 /**
  * Expert: {@link IndexWriter} uses an instance implementing this interface to execute the merges
@@ -34,8 +32,6 @@
  */
 public abstract class MergeScheduler implements Closeable {
 
-  private final Executor executor = new SameThreadExecutorService();
-
   /** Sole constructor. (For invocation by subclass constructors, typically implicit.) */
   protected MergeScheduler() {}
 
@@ -56,15 +52,6 @@
     return in;
   }
 
-  /**
-   * Provides an executor for parallelism during a single merge operation. By default, the method
-   * returns a {@link SameThreadExecutorService} where all intra-merge actions occur in their
-   * calling thread.
-   */
-  public Executor getIntraMergeExecutor(OneMerge merge) {
-    return executor;
-  }
-
   /** Close this MergeScheduler. */
   @Override
   public abstract void close() throws IOException;
diff --git a/lucene/core/src/java/org/apache/lucene/index/MergeState.java b/lucene/core/src/java/org/apache/lucene/index/MergeState.java
index de3c8d8..6153a57 100644
--- a/lucene/core/src/java/org/apache/lucene/index/MergeState.java
+++ b/lucene/core/src/java/org/apache/lucene/index/MergeState.java
@@ -21,7 +21,6 @@
 import java.io.IOException;
 import java.util.List;
 import java.util.Locale;
-import java.util.concurrent.Executor;
 import java.util.concurrent.TimeUnit;
 import org.apache.lucene.codecs.DocValuesProducer;
 import org.apache.lucene.codecs.FieldsProducer;
@@ -85,23 +84,15 @@
   /** InfoStream for debugging messages. */
   public final InfoStream infoStream;
 
-  /** Executor for intra merge activity */
-  public final Executor intraMergeTaskExecutor;
-
   /** Indicates if the index needs to be sorted * */
   public boolean needsIndexSort;
 
   /** Sole constructor. */
-  MergeState(
-      List<CodecReader> readers,
-      SegmentInfo segmentInfo,
-      InfoStream infoStream,
-      Executor intraMergeTaskExecutor)
+  MergeState(List<CodecReader> readers, SegmentInfo segmentInfo, InfoStream infoStream)
       throws IOException {
     verifyIndexSort(readers, segmentInfo);
     this.infoStream = infoStream;
     int numReaders = readers.size();
-    this.intraMergeTaskExecutor = intraMergeTaskExecutor;
 
     maxDocs = new int[numReaders];
     fieldsProducers = new FieldsProducer[numReaders];
diff --git a/lucene/core/src/java/org/apache/lucene/index/NoMergeScheduler.java b/lucene/core/src/java/org/apache/lucene/index/NoMergeScheduler.java
index fd6d2a8..0142288 100644
--- a/lucene/core/src/java/org/apache/lucene/index/NoMergeScheduler.java
+++ b/lucene/core/src/java/org/apache/lucene/index/NoMergeScheduler.java
@@ -16,7 +16,6 @@
  */
 package org.apache.lucene.index;
 
-import java.util.concurrent.Executor;
 import org.apache.lucene.index.MergePolicy.OneMerge;
 import org.apache.lucene.store.Directory;
 
@@ -53,9 +52,4 @@
   public MergeScheduler clone() {
     return this;
   }
-
-  @Override
-  public Executor getIntraMergeExecutor(OneMerge merge) {
-    throw new UnsupportedOperationException("NoMergeScheduler does not support merges");
-  }
 }
diff --git a/lucene/core/src/java/org/apache/lucene/index/SegmentMerger.java b/lucene/core/src/java/org/apache/lucene/index/SegmentMerger.java
index 4589f7e..7fc2f04 100644
--- a/lucene/core/src/java/org/apache/lucene/index/SegmentMerger.java
+++ b/lucene/core/src/java/org/apache/lucene/index/SegmentMerger.java
@@ -17,10 +17,7 @@
 package org.apache.lucene.index;
 
 import java.io.IOException;
-import java.util.ArrayList;
 import java.util.List;
-import java.util.concurrent.Callable;
-import java.util.concurrent.Executor;
 import java.util.concurrent.TimeUnit;
 import org.apache.lucene.codecs.Codec;
 import org.apache.lucene.codecs.DocValuesConsumer;
@@ -31,7 +28,6 @@
 import org.apache.lucene.codecs.PointsWriter;
 import org.apache.lucene.codecs.StoredFieldsWriter;
 import org.apache.lucene.codecs.TermVectorsWriter;
-import org.apache.lucene.search.TaskExecutor;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.store.IOContext;
 import org.apache.lucene.util.InfoStream;
@@ -60,14 +56,13 @@
       InfoStream infoStream,
       Directory dir,
       FieldInfos.FieldNumbers fieldNumbers,
-      IOContext context,
-      Executor intraMergeTaskExecutor)
+      IOContext context)
       throws IOException {
     if (context.context != IOContext.Context.MERGE) {
       throw new IllegalArgumentException(
           "IOContext.context should be MERGE; got: " + context.context);
     }
-    mergeState = new MergeState(readers, segmentInfo, infoStream, intraMergeTaskExecutor);
+    mergeState = new MergeState(readers, segmentInfo, infoStream);
     directory = dir;
     this.codec = segmentInfo.getCodec();
     this.context = context;
@@ -135,36 +130,19 @@
             IOContext.READ,
             segmentWriteState.segmentSuffix);
 
-    TaskExecutor taskExecutor = new TaskExecutor(mergeState.intraMergeTaskExecutor);
-    List<Callable<Void>> mergingTasks = new ArrayList<>();
-    mergingTasks.add(
-        () -> {
-          if (mergeState.mergeFieldInfos.hasNorms()) {
-            mergeWithLogging(
-                this::mergeNorms, segmentWriteState, segmentReadState, "norms", numMerged);
-          }
+    if (mergeState.mergeFieldInfos.hasNorms()) {
+      mergeWithLogging(this::mergeNorms, segmentWriteState, segmentReadState, "norms", numMerged);
+    }
 
-          mergeWithLogging(
-              this::mergeTerms, segmentWriteState, segmentReadState, "postings", numMerged);
-          return null;
-        });
+    mergeWithLogging(this::mergeTerms, segmentWriteState, segmentReadState, "postings", numMerged);
 
     if (mergeState.mergeFieldInfos.hasDocValues()) {
-      mergingTasks.add(
-          () -> {
-            mergeWithLogging(
-                this::mergeDocValues, segmentWriteState, segmentReadState, "doc values", numMerged);
-            return null;
-          });
+      mergeWithLogging(
+          this::mergeDocValues, segmentWriteState, segmentReadState, "doc values", numMerged);
     }
 
     if (mergeState.mergeFieldInfos.hasPointValues()) {
-      mergingTasks.add(
-          () -> {
-            mergeWithLogging(
-                this::mergePoints, segmentWriteState, segmentReadState, "points", numMerged);
-            return null;
-          });
+      mergeWithLogging(this::mergePoints, segmentWriteState, segmentReadState, "points", numMerged);
     }
 
     if (mergeState.mergeFieldInfos.hasVectorValues()) {
@@ -177,14 +155,9 @@
     }
 
     if (mergeState.mergeFieldInfos.hasVectors()) {
-      mergingTasks.add(
-          () -> {
-            mergeWithLogging(this::mergeTermVectors, "term vectors");
-            return null;
-          });
+      mergeWithLogging(this::mergeTermVectors, "term vectors");
     }
 
-    taskExecutor.invokeAll(mergingTasks);
     // write the merged infos
     mergeWithLogging(
         this::mergeFieldInfos, segmentWriteState, segmentReadState, "field infos", numMerged);
diff --git a/lucene/core/src/test/org/apache/lucene/codecs/lucene99/TestLucene99HnswQuantizedVectorsFormat.java b/lucene/core/src/test/org/apache/lucene/codecs/lucene99/TestLucene99HnswQuantizedVectorsFormat.java
index 66ae7bc..382389b 100644
--- a/lucene/core/src/test/org/apache/lucene/codecs/lucene99/TestLucene99HnswQuantizedVectorsFormat.java
+++ b/lucene/core/src/test/org/apache/lucene/codecs/lucene99/TestLucene99HnswQuantizedVectorsFormat.java
@@ -180,6 +180,9 @@
         () -> new Lucene99HnswScalarQuantizedVectorsFormat(20, 100, 0, 0.8f, null));
     expectThrows(
         IllegalArgumentException.class,
+        () -> new Lucene99HnswScalarQuantizedVectorsFormat(20, 100, 100, null, null));
+    expectThrows(
+        IllegalArgumentException.class,
         () ->
             new Lucene99HnswScalarQuantizedVectorsFormat(
                 20, 100, 1, null, new SameThreadExecutorService()));
diff --git a/lucene/core/src/test/org/apache/lucene/codecs/lucene99/TestLucene99HnswVectorsFormat.java b/lucene/core/src/test/org/apache/lucene/codecs/lucene99/TestLucene99HnswVectorsFormat.java
index 493b2cd..c444802 100644
--- a/lucene/core/src/test/org/apache/lucene/codecs/lucene99/TestLucene99HnswVectorsFormat.java
+++ b/lucene/core/src/test/org/apache/lucene/codecs/lucene99/TestLucene99HnswVectorsFormat.java
@@ -50,6 +50,8 @@
     expectThrows(IllegalArgumentException.class, () -> new Lucene99HnswVectorsFormat(512 + 1, 20));
     expectThrows(IllegalArgumentException.class, () -> new Lucene99HnswVectorsFormat(20, 3201));
     expectThrows(
+        IllegalArgumentException.class, () -> new Lucene99HnswVectorsFormat(20, 100, 100, null));
+    expectThrows(
         IllegalArgumentException.class,
         () -> new Lucene99HnswVectorsFormat(20, 100, 1, new SameThreadExecutorService()));
   }
diff --git a/lucene/core/src/test/org/apache/lucene/index/TestConcurrentMergeScheduler.java b/lucene/core/src/test/org/apache/lucene/index/TestConcurrentMergeScheduler.java
index 08b9bf9..17ea6e8 100644
--- a/lucene/core/src/test/org/apache/lucene/index/TestConcurrentMergeScheduler.java
+++ b/lucene/core/src/test/org/apache/lucene/index/TestConcurrentMergeScheduler.java
@@ -20,20 +20,16 @@
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Collections;
-import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.CountDownLatch;
-import java.util.concurrent.Executor;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
-import org.apache.lucene.codecs.Codec;
 import org.apache.lucene.document.Document;
 import org.apache.lucene.document.Field;
-import org.apache.lucene.document.KnnFloatVectorField;
 import org.apache.lucene.document.StringField;
 import org.apache.lucene.document.TextField;
 import org.apache.lucene.index.IndexWriterConfig.OpenMode;
@@ -46,10 +42,7 @@
 import org.apache.lucene.tests.util.LuceneTestCase;
 import org.apache.lucene.tests.util.TestUtil;
 import org.apache.lucene.util.InfoStream;
-import org.apache.lucene.util.SameThreadExecutorService;
-import org.apache.lucene.util.StringHelper;
 import org.apache.lucene.util.SuppressForbidden;
-import org.apache.lucene.util.Version;
 
 public class TestConcurrentMergeScheduler extends LuceneTestCase {
 
@@ -97,22 +90,12 @@
                   || (th instanceof IllegalStateException
                       && th.getMessage().contains("this writer hit an unrecoverable error"));
             }
-
-            @Override
-            // override here to ensure even tiny merges get the parallel executor
-            public Executor getIntraMergeExecutor(MergePolicy.OneMerge merge) {
-              assert intraMergeExecutor != null : "intraMergeExecutor is not initialized";
-              return intraMergeExecutor;
-            }
           });
     }
     IndexWriter writer = new IndexWriter(directory, iwc);
     Document doc = new Document();
     Field idField = newStringField("id", "", Field.Store.YES);
-    KnnFloatVectorField knnField = new KnnFloatVectorField("knn", new float[] {0.0f, 0.0f});
     doc.add(idField);
-    // Add knn float vectors to test parallel merge
-    doc.add(knnField);
 
     outer:
     for (int i = 0; i < 10; i++) {
@@ -122,7 +105,6 @@
 
       for (int j = 0; j < 20; j++) {
         idField.setStringValue(Integer.toString(i * 20 + j));
-        knnField.setVectorValue(new float[] {random().nextFloat(), random().nextFloat()});
         writer.addDocument(doc);
       }
 
@@ -244,35 +226,23 @@
     Directory directory = newDirectory();
     Document doc = new Document();
     Field idField = newStringField("id", "", Field.Store.YES);
-    KnnFloatVectorField knnField = new KnnFloatVectorField("knn", new float[] {0.0f, 0.0f});
     doc.add(idField);
-    doc.add(knnField);
-    IndexWriterConfig iwc =
-        newIndexWriterConfig(new MockAnalyzer(random()))
-            // Force excessive merging:
-            .setMaxBufferedDocs(2)
-            .setMergePolicy(newLogMergePolicy(100))
-            .setCommitOnClose(false);
-    if (iwc.getMergeScheduler() instanceof ConcurrentMergeScheduler) {
-      iwc.setMergeScheduler(
-          new ConcurrentMergeScheduler() {
-            @Override
-            // override here to ensure even tiny merges get the parallel executor
-            public Executor getIntraMergeExecutor(MergePolicy.OneMerge merge) {
-              assert intraMergeExecutor != null : "scaledExecutor is not initialized";
-              return intraMergeExecutor;
-            }
-          });
-    }
 
-    IndexWriter writer = new IndexWriter(directory, iwc);
+    IndexWriter writer =
+        new IndexWriter(
+            directory,
+            newIndexWriterConfig(new MockAnalyzer(random()))
+                .
+                // Force excessive merging:
+                setMaxBufferedDocs(2)
+                .setMergePolicy(newLogMergePolicy(100))
+                .setCommitOnClose(false));
 
     int numIters = TEST_NIGHTLY ? 10 : 3;
     for (int iter = 0; iter < numIters; iter++) {
 
       for (int j = 0; j < 201; j++) {
         idField.setStringValue(Integer.toString(iter * 201 + j));
-        knnField.setVectorValue(new float[] {random().nextFloat(), random().nextFloat()});
         writer.addDocument(doc);
       }
 
@@ -394,118 +364,6 @@
     dir.close();
   }
 
-  public void testSmallMergesDonNotGetThreads() throws IOException {
-    Directory dir = newDirectory();
-    IndexWriterConfig iwc = new IndexWriterConfig(new MockAnalyzer(random()));
-    iwc.setMaxBufferedDocs(2);
-    iwc.setMergeScheduler(
-        new ConcurrentMergeScheduler() {
-          @Override
-          protected void doMerge(MergeSource mergeSource, MergePolicy.OneMerge merge)
-              throws IOException {
-            assertTrue(this.getIntraMergeExecutor(merge) instanceof SameThreadExecutorService);
-            super.doMerge(mergeSource, merge);
-          }
-        });
-    IndexWriter w = new IndexWriter(dir, iwc);
-    for (int i = 0; i < 10; i++) {
-      Document doc = new Document();
-      doc.add(new StringField("id", "" + i, Field.Store.NO));
-      w.addDocument(doc);
-    }
-    w.forceMerge(1);
-    w.close();
-    dir.close();
-  }
-
-  @SuppressForbidden(reason = "Thread sleep")
-  public void testIntraMergeThreadPoolIsLimitedByMaxThreads() throws IOException {
-    ConcurrentMergeScheduler mergeScheduler = new ConcurrentMergeScheduler();
-    MergeScheduler.MergeSource mergeSource =
-        new MergeScheduler.MergeSource() {
-          @Override
-          public MergePolicy.OneMerge getNextMerge() {
-            fail("should not be called");
-            return null;
-          }
-
-          @Override
-          public void onMergeFinished(MergePolicy.OneMerge merge) {
-            fail("should not be called");
-          }
-
-          @Override
-          public boolean hasPendingMerges() {
-            fail("should not be called");
-            return false;
-          }
-
-          @Override
-          public void merge(MergePolicy.OneMerge merge) throws IOException {
-            fail("should not be called");
-          }
-        };
-    try (Directory dir = newDirectory();
-        mergeScheduler) {
-      MergePolicy.OneMerge merge =
-          new MergePolicy.OneMerge(
-              List.of(
-                  new SegmentCommitInfo(
-                      new SegmentInfo(
-                          dir,
-                          Version.LATEST,
-                          null,
-                          "test",
-                          0,
-                          false,
-                          false,
-                          Codec.getDefault(),
-                          Collections.emptyMap(),
-                          StringHelper.randomId(),
-                          new HashMap<>(),
-                          null),
-                      0,
-                      0,
-                      0,
-                      0,
-                      0,
-                      new byte[16])));
-      mergeScheduler.initialize(InfoStream.NO_OUTPUT, dir);
-      mergeScheduler.setMaxMergesAndThreads(6, 6);
-      Executor executor = mergeScheduler.intraMergeExecutor;
-      AtomicInteger threadsExecutedOnPool = new AtomicInteger();
-      AtomicInteger threadsExecutedOnSelf = new AtomicInteger();
-      for (int i = 0; i < 4; i++) {
-        mergeScheduler.mergeThreads.add(
-            mergeScheduler.new MergeThread(mergeSource, merge) {
-              @Override
-              @SuppressForbidden(reason = "Thread sleep")
-              public void run() {
-                executor.execute(
-                    () -> {
-                      if (Thread.currentThread() == this) {
-                        threadsExecutedOnSelf.incrementAndGet();
-                      } else {
-                        threadsExecutedOnPool.incrementAndGet();
-                      }
-                      try {
-                        Thread.sleep(100);
-                      } catch (InterruptedException e) {
-                        throw new RuntimeException(e);
-                      }
-                    });
-              }
-            });
-      }
-      for (ConcurrentMergeScheduler.MergeThread thread : mergeScheduler.mergeThreads) {
-        thread.start();
-      }
-      mergeScheduler.sync();
-      assertEquals(3, threadsExecutedOnSelf.get());
-      assertEquals(1, threadsExecutedOnPool.get());
-    }
-  }
-
   private static class TrackingCMS extends ConcurrentMergeScheduler {
     long totMergedBytes;
     CountDownLatch atLeastOneMerge;
diff --git a/lucene/core/src/test/org/apache/lucene/index/TestDoc.java b/lucene/core/src/test/org/apache/lucene/index/TestDoc.java
index 0cdd645..3b245dd 100644
--- a/lucene/core/src/test/org/apache/lucene/index/TestDoc.java
+++ b/lucene/core/src/test/org/apache/lucene/index/TestDoc.java
@@ -45,7 +45,6 @@
 import org.apache.lucene.tests.util.LuceneTestCase;
 import org.apache.lucene.util.Bits;
 import org.apache.lucene.util.InfoStream;
-import org.apache.lucene.util.SameThreadExecutorService;
 import org.apache.lucene.util.StringHelper;
 import org.apache.lucene.util.Version;
 
@@ -238,8 +237,7 @@
             InfoStream.getDefault(),
             trackingDir,
             new FieldInfos.FieldNumbers(null, null),
-            context,
-            new SameThreadExecutorService());
+            context);
 
     merger.merge();
     r1.close();
diff --git a/lucene/core/src/test/org/apache/lucene/index/TestSegmentMerger.java b/lucene/core/src/test/org/apache/lucene/index/TestSegmentMerger.java
index 94a1849..615accb 100644
--- a/lucene/core/src/test/org/apache/lucene/index/TestSegmentMerger.java
+++ b/lucene/core/src/test/org/apache/lucene/index/TestSegmentMerger.java
@@ -32,7 +32,6 @@
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.FixedBitSet;
 import org.apache.lucene.util.InfoStream;
-import org.apache.lucene.util.SameThreadExecutorService;
 import org.apache.lucene.util.StringHelper;
 import org.apache.lucene.util.Version;
 import org.apache.lucene.util.packed.PackedLongValues;
@@ -106,8 +105,7 @@
             InfoStream.getDefault(),
             mergedDir,
             new FieldInfos.FieldNumbers(null, null),
-            newIOContext(random(), new IOContext(new MergeInfo(-1, -1, false, -1))),
-            new SameThreadExecutorService());
+            newIOContext(random(), new IOContext(new MergeInfo(-1, -1, false, -1))));
     MergeState mergeState = merger.merge();
     int docsMerged = mergeState.segmentInfo.maxDoc();
     assertTrue(docsMerged == 2);