Delete crash safe index file if index file exists

Summary:
Crash safe index file is created when any change is made to the index
file. The index file is first copied over to the crash safe one and then stuff
is added/removed from the crash safe index file. Finally, the old index file is
deleted and crash safe index file is renamed to the index file. There might be a
scenario where mysql crashes after stuff is changed in the crash safe file
but before the old index file is deleted. In this case we should delete the
crash safe index file at restart. If we don't delete it subsequent changes to
the index file can corrupt it because it can be copied to the old crash safe
file which already has some data in it.
Closes #433

Reviewed By: santoshbanda

Differential Revision: D4198274

Pulled By: abhinav04sharma

fbshipit-source-id: a6f8993

sql/binlog.cc

@@ -2750,18 +2750,35 @@ bool MYSQL_BIN_LOG::open_index_file(const char *index_file_name_arg,
     return TRUE;
   }
 
-  /*
-    We need move crash_safe_index_file to index_file if the index_file
-    does not exist and crash_safe_index_file exists when mysqld server
-    restarts.
-  */
-  if (my_access(index_file_name, F_OK) &&
-      !my_access(crash_safe_index_file_name, F_OK) &&
-      my_rename(crash_safe_index_file_name, index_file_name, MYF(MY_WME)))
+  // case: crash_safe_index_file exists
+  if (!my_access(crash_safe_index_file_name, F_OK))
   {
-    sql_print_error("MYSQL_BIN_LOG::open_index_file failed to "
-                    "move crash_safe_index_file to index file.");
-    return TRUE;
+    /*
+      We need move crash_safe_index_file to index_file if the index_file
+      does not exist or delete it if the index_file exists when mysqld server
+      restarts.
+    */
+
+    // case: index_file does not exist
+    if (my_access(index_file_name, F_OK))
+    {
+      if (my_rename(crash_safe_index_file_name, index_file_name, MYF(MY_WME)))
+      {
+        sql_print_error("MYSQL_BIN_LOG::open_index_file failed to "
+            "move crash_safe_index_file to index_file.");
+        return TRUE;
+      }
+
+    }
+    else
+    {
+      if (my_delete(crash_safe_index_file_name, MYF(MY_WME)))
+      {
+        sql_print_error("MYSQL_BIN_LOG::open_index_file failed to "
+            "delete crash_safe_index_file.");
+        return TRUE;
+      }
+    }
   }
 
   if ((index_file_nr= mysql_file_open(m_key_file_log_index,