Bug #46957 Innodb on windows doesn't do concurrent IO per file

• Submitted: 27 Aug 2009 15:15
• Modified: 9 Sep 2009 15:53
• Reporter: Mark Callaghan
• Status: Not a Bug
• Category: MySQL Server: InnoDB storage engine
• Severity: S5 (Performance)
• Version: 5.0,5.1,plugin
• OS: Windows
• CPU Architecture: Any
• Tags: innodb, performance, windows

[27 Aug 2009 15:15] Mark Callaghan

Description:
Innodb uses os_file_read and os_file_write to read and write from files. Both of these hold a mutex while calling SetFilePointer/WriteFile or SetFilePointer/ReadFile. This is done because WriteFile and ReadFile apparently do not support positioned reads (pread) and positioned writes (pwrite) so the mutex is held while the offset to the file is set.

Because of this there can be at most one file IO request pending per file. You really need to use innodb_file_per_table in this case.

How to repeat:
Read os_file_read and os_file_write. Look for '#ifdef __WIN__'.

Suggested fix:
I don't know.

[27 Aug 2009 20:26] Peter Laursen

@Mark .. your synopsis reads "Innodb on windows .." but the OS field reads 'any'. Please clarify!

[27 Aug 2009 20:36] Mark Callaghan

set OS to Windows

[1 Sep 2009 2:10] Mark Callaghan

Mikael Ronstrom might have more background on this. After reading more of the code, I think Win XP and more recent windows are OK:
>>>
On reading the code again, when os_aio_use_native_aio is set, then async IO is used for all (most?) IO requests from InnoDB. And it is set on windows as long as os_get_os_version() != OS_WIN95, OS_WIN31, OS_WINNT. 

So, InnoDB IO performance on Win XP and more recent systems might be better than it is on Linux.
>>>

[9 Sep 2009 15:44] Calvin Sun

Async IO is default on Windows.

[9 Sep 2009 15:53] Mark Callaghan

Yes, I updated my blog but not the bug after figuring out how that is done. To be pedantic, this is supported for modern windows (XP or greater) not Windows. The code which serializes IO is used for older Windows releases.

[9 Sep 2009 15:59] Peter Laursen

@Mark .. it was not pedantic.  It was very pedantic!

All Windows versions before XP are *totally dead*. Not supported by Microsoft for several years. 'Windows' and 'Windows XP and later' are synonyms.