Bug#16212207 - LOAD XML INFILE PERFORMANCE WITH INDENTED

               XML

DESCRIPTION
===========
LOAD XML INFILE performance becomes painfully slow if the
tags' value has any space(s) in between them. They're
usually kept intentionally for indentation purpose.

ANALYSIS
========
The extra spaces are calling clear_level() many a times
which is having overhead of clearing taglist etc. This can
be avoided altogether by skipping all such spaces.

FIX
===
Trim all the starting whitespaces from the value before
passing it to read_value()

sql/sql_load.cc

 /*
-   Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.
+   Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -1989,6 +1989,13 @@ int READ_INFO::read_xml()
       
     case '>': /* end tag - read tag value */
       in_tag= false;
+      /* Skip all whitespaces */
+      while (' ' == (chr= my_tospace(GET)));
+      /*
+        Push the first non-whitespace char back to Stack. This char would be
+        read in the upcoming call to read_value()
+       */
+      PUSH(chr);
       chr= read_value('<', &value);
       if(chr == my_b_EOF)
         goto found_eof;