Also align temp file used during merge

Author: Kaival Parikh

lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99FlatVectorsWriter.java

@@ -257,13 +257,13 @@ public void mergeOneField(FieldInfo fieldInfo, MergeState mergeState) throws IOE
   @Override
   public CloseableRandomVectorScorerSupplier mergeOneFieldToIndex(
       FieldInfo fieldInfo, MergeState mergeState) throws IOException {
-    long vectorDataOffset = alignOutput(vectorData, fieldInfo.getVectorEncoding());
     IndexOutput tempVectorData =
         segmentWriteState.directory.createTempOutput(
             vectorData.getName(), "temp", segmentWriteState.context);
     IndexInput vectorDataInput = null;
     try {
       // write the vector data to a temporary file
+      long tempVectorDataOffset = alignOutput(tempVectorData, fieldInfo.getVectorEncoding());
       DocsWithFieldSet docsWithField =
           switch (fieldInfo.getVectorEncoding()) {
             case BYTE ->
@@ -277,6 +277,8 @@ public CloseableRandomVectorScorerSupplier mergeOneFieldToIndex(
                     KnnVectorsWriter.MergedVectorValues.mergeFloatVectorValues(
                         fieldInfo, mergeState));
           };
+      long vectorDataLength = tempVectorData.getFilePointer() - tempVectorDataOffset;
+
       CodecUtil.writeFooter(tempVectorData);
       IOUtils.close(tempVectorData);
 
@@ -288,10 +290,13 @@ public CloseableRandomVectorScorerSupplier mergeOneFieldToIndex(
               tempVectorData.getName(),
               IOContext.DEFAULT.withHints(
                   FileTypeHint.DATA, FileDataHint.KNN_VECTORS, DataAccessHint.RANDOM));
+      vectorDataInput.seek(tempVectorDataOffset);
+
       // copy the temporary file vectors to the actual data file
-      vectorData.copyBytes(vectorDataInput, vectorDataInput.length() - CodecUtil.footerLength());
+      long vectorDataOffset = alignOutput(vectorData, fieldInfo.getVectorEncoding());
+      vectorData.copyBytes(vectorDataInput, vectorDataLength);
+
       CodecUtil.retrieveChecksum(vectorDataInput);
-      long vectorDataLength = vectorData.getFilePointer() - vectorDataOffset;
       writeMeta(
           fieldInfo,
           segmentWriteState.segmentInfo.maxDoc(),
@@ -310,7 +315,8 @@ public CloseableRandomVectorScorerSupplier mergeOneFieldToIndex(
                     new OffHeapByteVectorValues.DenseOffHeapVectorValues(
                         fieldInfo.getVectorDimension(),
                         docsWithField.cardinality(),
-                        finalVectorDataInput,
+                        finalVectorDataInput.slice(
+                            "temp-vector-data", tempVectorDataOffset, vectorDataLength),
                         fieldInfo.getVectorDimension() * Byte.BYTES,
                         vectorsScorer,
                         fieldInfo.getVectorSimilarityFunction()));
@@ -320,7 +326,8 @@ public CloseableRandomVectorScorerSupplier mergeOneFieldToIndex(
                     new OffHeapFloatVectorValues.DenseOffHeapVectorValues(
                         fieldInfo.getVectorDimension(),
                         docsWithField.cardinality(),
-                        finalVectorDataInput,
+                        finalVectorDataInput.slice(
+                            "temp-vector-data", tempVectorDataOffset, vectorDataLength),
                         fieldInfo.getVectorDimension() * Float.BYTES,
                         vectorsScorer,
                         fieldInfo.getVectorSimilarityFunction()));