Change Variable name in openMergeDB (#228)

Change the name of the db variable to mergeDB to avoid confusion

---------

Co-authored-by: roseduan <[email protected]>

merge.go

@@ -25,7 +25,7 @@ const (
 // So it is recommended to perform this operation when the database is idle.
 func (db *DB) Merge() error {
 	db.mu.Lock()
-	// check if the daabase is closed
+	// check if the database is closed
 	if db.closed {
 		db.mu.Unlock()
 		return ErrDBClosed
@@ -129,13 +129,12 @@ func (db *DB) openMergeDB() (*DB, error) {
 	if err := os.RemoveAll(mergePath); err != nil {
 		return nil, err
 	}
-
 	options := db.options
 	// we don't need to use the original sync policy,
 	// because we can sync the data file manually after the merge operation is completed.
 	options.Sync, options.BytesPerSync = false, 0
 	options.DirPath = mergePath
-	db, err := Open(options)
+	mergeDB, err := Open(options)
 	if err != nil {
 		return nil, err
 	}
@@ -153,9 +152,8 @@ func (db *DB) openMergeDB() (*DB, error) {
 	if err != nil {
 		return nil, err
 	}
-
-	db.hintFile = hintFile
-	return db, nil
+	mergeDB.hintFile = hintFile
+	return mergeDB, nil
 }
 
 func mergeDirPath(dirPath string) string {
@@ -339,6 +337,7 @@ func (db *DB) loadIndexFromHintFile() error {
 			}
 			return err
 		}
+
 		key, position := decodeHintRecord(chunk)
 		// All the hint records are valid because it is generated by the merge operation.
 		// So just put them into the index without checking.