Bug #71479 sort_buffer_size is limited to 4GB-1 on 64-bit Windows

Description:
Manual (http://dev.mysql.com/doc/refman/5.6/en/server-system-variables.html#sysvar_sort_buffer_siz...) says:

"The maximum permissible setting for sort_buffer_size is 4GB. Values larger than 4GB are permitted for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB with a warning)."

But in fact (on 5.6.15 running on 64-bit Windows 7 at least) the limit is 4*1024*1024*1024-1 (4GB-1):

mysql> set session sort_buffer_size=4*1024*1024*1024-1;
Query OK, 0 rows affected (0.06 sec)

mysql> set session sort_buffer_size=4*1024*1024*1024;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> show warnings\G
*************************** 1. row ***************************
  Level: Warning
   Code: 1292
Message: Truncated incorrect sort_buffer_size value: '4294967296'
1 row in set (0.00 sec)

mysql> show variables like 'version%';
+-------------------------+------------------------------+
| Variable_name           | Value                        |
+-------------------------+------------------------------+
| version                 | 5.6.15-log                   |
| version_comment         | MySQL Community Server (GPL) |
| version_compile_machine | x86_64                       |
| version_compile_os      | Win64                        |
+-------------------------+------------------------------+
4 rows in set (0.00 sec)

mysql> show variables like 'sort_buffer_size';
+------------------+------------+
| Variable_name    | Value      |
+------------------+------------+
| sort_buffer_size | 4294967295 |
+------------------+------------+
1 row in set (0.00 sec)

How to repeat:
On 64-bit Windows try these:

set session sort_buffer_size=4*1024*1024*1024-1;
show variables like 'sort_buffer_size';
set session sort_buffer_size=4*1024*1024*1024;
show warnings\G
show variables like 'sort_buffer_size';

show variables like 'version%';

Suggested fix:
Document the limit properly in the manual.

Hello Valeriy,

Thank you for the bug report.
Verified as described.

Thanks,
Umesh

but why does this limit apply to windows and not linux?  shouldn't the limit rather be removed instead of document it?

Good question, Shane... I suspect some (wrong?) data type is used for the related variable on Windows for some historical reason (like "nobody cared to ask"). 

I don't mind to see this re-classified as a server bug.

Perhaps there are two issues here:

1) The off-by-one error in the description in the docs (4GB rather than 4GB-1). I can deal with this.

2) The capping of the value for Windows 64-bit, as opposed to other 64-bit systems.

Similar capping applies to join_buffer_size, key_buffer_size, myisam_sort_buffer_size, where the limit was lifted for non-Windows 64-bit systems in 5.1.23. The limit on Windows was lifted for key_buffer_size in 5.1.31; not sure why it wouldn't have been lifted for the others. Maybe it could be, in which case this might better be considered a server bug, or feature request.

Off-by-one aspect of the docs description has been fixed.

Unassigning from myself; no longer a docs bug.