diff --git a/storage/rocksdb/rdb_index_merge.h b/storage/rocksdb/rdb_index_merge.h
index ce602c882ba760378551cde92f507218e586f632..9bdfc1d600f8f8ab8802fa9836dbaaaad3a61b84 100644
--- a/storage/rocksdb/rdb_index_merge.h
+++ b/storage/rocksdb/rdb_index_merge.h
@@ -45,4 +45,22 @@ class Rdb_tbl_def;
 
 class Rdb_index_merge {
   Rdb_index_merge(const Rdb_index_merge &p) = delete;
-  Rdb_index_merge &operator=(const Rdb_index_merge &p) = delete;
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+  Rdb_index_merge &operator=(const Rdb_index_merge &p) = delete;
+
+ public:
+  /* Information about temporary files used in external merge sort */
+  struct merge_file_info {
+    File m_fd = -1;               /* file descriptor */
+    ulong m_num_sort_buffers = 0; /* number of sort buffers in temp file */
+  };
+
+  /* Buffer for sorting in main memory. */
+  struct merge_buf_info {
+    /* heap memory allocated for main memory sort/merge  */
+    std::unique_ptr<uchar[]> m_block;
+    const ulonglong
+        m_block_len; /* amount of data bytes allocated for block above */
+    ulonglong m_curr_offset; /* offset of the record pointer for the block */
+    ulonglong m_disk_start_offset; /* where the chunk starts on disk */
+    ulonglong m_disk_curr_offset;  /* current offset on disk */
+    ulonglong m_total_size;        /* total # of data bytes in chunk */
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