Description:
In the bug report mysqlbug14637(http://bugs.mysql.com/bug.php?id=14637), reporter finds that two functions, my_hash_sort_simple() and my_lengthsp_8bit(), trim blank spaces from the end of a string. These two functions parse the string byte wise and are quite slow for longer strings.
The patch for this bug has a string length threshold. If the string length is shorter than the threshold, it will perform byte wise comparison. And if the string length is longer than the threshold, it will perform word wise comparison. After employing this patch, we will not get a worse performance, and in some situation, we will get better performance.
In the bug report http://bugs.mysql.com/bug.php?id=60348, I report some trim trailing blank spaces code places, which can use the patch directly. After that, I check the code again, and find some trim beginning blank spaces code places. I think they should be patched in a similar way.
I list the places I found as follows:
1 /mysql-5.1.55/mysys/my_handler.c:68
if (piks &&
for (end= a + a_length-length; a < end ; a++)
{
if (*a != ' ')
return (*a < ' ') ? -swap : swap;
}
===============================================================================
2 /mysql-5.1.55/mysys/mf_format.c:139
while (*++pos == ' ') {}; /* Use old extension */
===============================================================================
3 /mysql-5.1.55/mysys/mf_wfile.c:42
while (*str == ' ')
str++;
===============================================================================
4 /mysql-5.1.55/mysys/mf_wfile.c:47
while (*++str == ' ') {};
===============================================================================
5 /mysql-5.1.55/mysys/typelib.c:94
while (*i == ' ')
while (*i == ' ')
i++; /* skip_end_space */
===============================================================================
6 mysql-5.1.55/mysys/my_handler.c:383
for ( ; alength && *a == ' ' ; a++, alength--) ;
===============================================================================
7 /mysql-5.1.55/mysys/my_handler.c:384
for ( ; blength && *b == ' ' ; b++, blength--) ;
===============================================================================
8 /mysql-5.1.55/client/mysqladmin.cc:710
while (*status == ' ') status++; /* to next info */
===============================================================================
9 /mysql-5.1.55/client/mysql.cc:4460
while (*status_str == ' ')
while (*status_str == ' ')
status_str++; /* to next info */
===============================================================================
10 /mysql-5.1.55/client/mysqltest.cc:4594
while (*p && *p == ' ')
while (*p && *p == ' ')
p++;
===============================================================================
11 /mysql-5.1.55/client/mysqltest.cc:1017
while (*ptr && *ptr == ' ')
ptr++;
===============================================================================
12 /mysql-5.1.55/storage/innobase/rem/rem0cmp.c:177
for (; a_length && *a == ' '; a++, a_length--);
===============================================================================
13 /mysql-5.1.55/storage/innodb_plugin/rem/rem0cmp.c:187
for (; a_length && *a == ' '; a++, a_length--);
===============================================================================
14 /mysql-5.1.55/storage/myisam/mi_search.c:475
for ( ; k < k_end && *k == ' '; k++) ;
===============================================================================
15 /mysql-5.1.55/storage/myisam/mi_key.c:259
while (pos < end && pos[0] == ' ')
pos++;
===============================================================================
16 /mysql-5.1.55/storage/myisam/mi_dynrec.c:1158
while (pos < end && *pos == ' ')
pos++;
===============================================================================
17 /mysql-5.1.55/storage/myisam/mi_dynrec.c:1038
while (pos < end && *pos == ' ')
pos++;
===============================================================================
18 /mysql-5.1.55/storage/myisam/myisampack.c:2586
for (pos=start_pos ; pos < end_pos && pos[0] == ' ' ; pos++) ;
===============================================================================
19 /mysql-5.1.55/sql/item_xmlfunc.cc:1359
for ( ; beg < end && *beg == ' ' ; beg++) ; // skip leading spaces
==============================================================================
20 /mysql-5.1.55/sql/field.cc:2363
for (str=ptr ; *str == ' ' ; str++) ;
==============================================================================
21 /mysql-5.1.55/sql/mysqld.cc:9075
while (*pos == ' ') pos++;
==============================================================================
22 /mysql-5.1.55/sql/sql_cache.cc:587
while (sql[i] == ' ')
++i;
How to repeat:
code review
Suggested fix:
static inline const uchar *skip_beginning_space(const uchar *ptr,size_t len)
{
const uchar *end= ptr + len;
if (len > 20)
{
const uchar *end_words= (const uchar *)(intptr)
(((ulonglong)(intptr)end) / SIZEOF_INT * SIZEOF_INT);
const uchar *start_words= (const uchar *)(intptr)
((((ulonglong)(intptr)ptr) + SIZEOF_INT - 1) / SIZEOF_INT * SIZEOF_INT);
DBUG_ASSERT(((ulonglong)(intptr)ptr) >= SIZEOF_INT);
if (end > start_words)
{
while (ptr < start_words && ptr[0] == 0x20)
ptr++;
if (ptr[0] == 0x20 && start_words < end_words)
while (ptr < end_words && ((unsigned *)ptr)[0] == SPACE_INT)
ptr += SIZEOF_INT;
}
}
while (ptr < end && ptr[0] == 0x20)
ptr++;
return (ptr);
}
