MySQL Bugs: #70848: Reduce the work inside critical section in my_fopen() and my_register

Bug #70848	Reduce the work inside critical section in my_fopen() and my_register_filename()
Submitted:	7 Nov 2013 3:22	Modified:	18 Nov 2013 15:51
Reporter:	Po-Chun Chang (OCA)	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server: Optimizer	Severity:	S5 (Performance)
Version:	5.7	OS:	Any
Assigned to:		CPU Architecture:	Any
Tags:	patch, performance

Description:
Hi,

The optimization chance appears in the latest revision 6313 in version 5.7.
I have attached two simple patches that enables it.

The function my_strdup() in mysys/my_fopen.c:my_fopen() will not use and
change the shared variables. Therefore it could be executed before the 
critical section defined by THR_LOCK_open, which reduces the work in the
critical section.

Similar optimization also appears in mysys/my_open.c:my_register_filename(),
in which the function my_strdup() could be executed before critical section
defined by THR_LOCK_open.

How to repeat:
Once my_fopen() or my_register_filename() executes.

Suggested fix:
Move the my_strdup() calls outside the critical section.

Suggested patch for my_fopen()

(*) I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it.

Contribution: patch1.diff (text/plain), 680 bytes.

Suggested patch for my_register_filename()

(*) I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it.

Contribution: patch2.diff (text/plain), 621 bytes.

Thank you for the bug report and contribution.

The following contributions were processed by development:

* Contribution 20732 in bug 17757953 (Oracle) / 70848 (MySQL)
* Contribution 20733 in bug 17757953 (Oracle) / 70848 (MySQL)

Noted in 5.7.4 changelog.

Overhead was reduced within critical sections of the my_fopen() and 
my_register_filename() mysys functions. Thanks to Po-Chun Chang for
the patch.