diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index 41ee5343e090..3a88efece170 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -214,6 +214,8 @@ Other
 * GITHUB#12428: Replace consecutive close() calls and close() calls with null checks with IOUtils.close().
   (Shubham Chaudhary)
 
+* GITHUB#12512: Remove unused variable in BKDWriter. (Chao Zhang)
+
 ======================== Lucene 9.7.0 =======================
 
 API Changes
diff --git a/lucene/core/src/java/org/apache/lucene/util/bkd/BKDWriter.java b/lucene/core/src/java/org/apache/lucene/util/bkd/BKDWriter.java
index b4b8f1fe66d0..5bea2e4ac5ae 100644
--- a/lucene/core/src/java/org/apache/lucene/util/bkd/BKDWriter.java
+++ b/lucene/core/src/java/org/apache/lucene/util/bkd/BKDWriter.java
@@ -103,8 +103,7 @@ public class BKDWriter implements Closeable {
   final double maxMBSortInHeap;
 
   final byte[] scratchDiff;
-  final byte[] scratch1;
-  final byte[] scratch2;
+  final byte[] scratch;
   final BytesRef scratchBytesRef1 = new BytesRef();
   final BytesRef scratchBytesRef2 = new BytesRef();
   final int[] commonPrefixLengths;
@@ -156,8 +155,7 @@ public BKDWriter(
     docsSeen = new FixedBitSet(maxDoc);
 
     scratchDiff = new byte[config.bytesPerDim];
-    scratch1 = new byte[config.packedBytesLength];
-    scratch2 = new byte[config.packedBytesLength];
+    scratch = new byte[config.packedBytesLength];
     commonPrefixLengths = new int[config.numDims];
 
     minPackedValue = new byte[config.packedIndexBytesLength];
@@ -1323,21 +1321,21 @@ private void writeLowCardinalityLeafBlockPackedValues(
       writeActualBounds(out, commonPrefixLengths, count, packedValues);
     }
     BytesRef value = packedValues.apply(0);
-    System.arraycopy(value.bytes, value.offset, scratch1, 0, config.packedBytesLength);
+    System.arraycopy(value.bytes, value.offset, scratch, 0, config.packedBytesLength);
     int cardinality = 1;
     for (int i = 1; i < count; i++) {
       value = packedValues.apply(i);
       for (int dim = 0; dim < config.numDims; dim++) {
         final int start = dim * config.bytesPerDim;
-        if (equalsPredicate.test(value.bytes, value.offset + start, scratch1, start) == false) {
+        if (equalsPredicate.test(value.bytes, value.offset + start, scratch, start) == false) {
           out.writeVInt(cardinality);
           for (int j = 0; j < config.numDims; j++) {
             out.writeBytes(
-                scratch1,
+                scratch,
                 j * config.bytesPerDim + commonPrefixLengths[j],
                 config.bytesPerDim - commonPrefixLengths[j]);
           }
-          System.arraycopy(value.bytes, value.offset, scratch1, 0, config.packedBytesLength);
+          System.arraycopy(value.bytes, value.offset, scratch, 0, config.packedBytesLength);
           cardinality = 1;
           break;
         } else if (dim == config.numDims - 1) {
@@ -1348,7 +1346,7 @@ private void writeLowCardinalityLeafBlockPackedValues(
     out.writeVInt(cardinality);
     for (int i = 0; i < config.numDims; i++) {
       out.writeBytes(
-          scratch1,
+          scratch,
           i * config.bytesPerDim + commonPrefixLengths[i],
           config.bytesPerDim - commonPrefixLengths[i]);
     }
@@ -1545,8 +1543,8 @@ protected int split(byte[] minPackedValue, byte[] maxPackedValue, int[] parentSp
     int splitDim = -1;
     for (int dim = 0; dim < config.numIndexDims; dim++) {
       NumericUtils.subtract(config.bytesPerDim, dim, maxPackedValue, minPackedValue, scratchDiff);
-      if (splitDim == -1 || comparator.compare(scratchDiff, 0, scratch1, 0) > 0) {
-        System.arraycopy(scratchDiff, 0, scratch1, 0, config.bytesPerDim);
+      if (splitDim == -1 || comparator.compare(scratchDiff, 0, scratch, 0) > 0) {
+        System.arraycopy(scratchDiff, 0, scratch, 0, config.bytesPerDim);
         splitDim = dim;
       }
     }
@@ -1688,8 +1686,8 @@ private void build(
       // Write the common prefixes:
       reader.getValue(from, scratchBytesRef1);
       System.arraycopy(
-          scratchBytesRef1.bytes, scratchBytesRef1.offset, scratch1, 0, config.packedBytesLength);
-      writeCommonPrefixes(out, commonPrefixLengths, scratch1);
+          scratchBytesRef1.bytes, scratchBytesRef1.offset, scratch, 0, config.packedBytesLength);
+      writeCommonPrefixes(out, commonPrefixLengths, scratch);
 
       // Write the full values:
       IntFunction<BytesRef> packedValues =
@@ -1886,8 +1884,8 @@ private void build(
 
       int from = Math.toIntExact(points.start);
       int to = Math.toIntExact(points.start + points.count);
-      // we store common prefix on scratch1
-      computeCommonPrefixLength(heapSource, scratch1, from, to);
+      // we store common prefix on scratch
+      computeCommonPrefixLength(heapSource, scratch, from, to);
 
       int sortedDim = 0;
       int sortedDimCardinality = Integer.MAX_VALUE;
@@ -1942,7 +1940,7 @@ private void build(
       // from the index, much like how terms dict does so from the FST:
 
       // Write the common prefixes:
-      writeCommonPrefixes(out, commonPrefixLengths, scratch1);
+      writeCommonPrefixes(out, commonPrefixLengths, scratch);
 
       // Write the full values:
       IntFunction<BytesRef> packedValues =