Bug #56791 Remove ios_mutex from InnoDB code
Submitted: 15 Sep 2010 10:32 Modified: 9 Dec 2010 22:44
Reporter: Jimmy Yang Email Updates:
Status: Closed Impact on me:
Category:MySQL Server: InnoDB storage engine Severity:S3 (Non-critical)
Version:5.5 OS:Any
Assigned to: Jimmy Yang CPU Architecture:Any

[15 Sep 2010 10:32] Jimmy Yang
We have a ios_mutex to protect counter "ios" in io_handler_thread():

/** Count of I/O operations in io_handler_thread() */
static ulint            ios;

        for (i = 0;; i++) {



This mutex is not necessary. We can make the counter increment atomic, or even if it is not atomic, no need to dedicate a mutex for this counter.

How to repeat:
See the code
[15 Sep 2010 15:30] MySQL Verification Team
Thank you for the bug report.
[21 Sep 2010 16:58] Omer Barnir
triage: setting to SRMRTBD (code cleanup)
[21 Oct 2010 12:34] Marko Mäkelä
The variable "ios" that is protected by "ios_mutex" is completely unused. It a static variable in srv0start.c that is only initialized or incremented, never read or copied. We should remove it as well. Because there is some contention on the useless ios_mutex, I think that this bug should be fixed already in 5.5, if not 5.1.
[21 Oct 2010 12:38] Jimmy Yang
Updated a few counters in the similar situation:

1) Removed ios_mutex
2) Added generic counter operation to increment/decrement following counters atomically if HAVE_ATOMIC_BUILTINS is defined:
 a) ios
 b) dict_table_t::n_foreign_key_checks_running
 c) trx_sys->rseg_history_len

We will fall back to mutex protection for "n_foreign_key_checks_running" and "rseg_history_len" if  HAVE_ATOMIC_BUILTINS not defined.
[21 Oct 2010 12:44] Calvin Sun
Fine with the fix in 5.1.
[21 Oct 2010 12:59] Jimmy Yang
We will use this patch just to remove ios_mutex and ios which is a static counter not being used.
[22 Oct 2010 6:39] Jimmy Yang
Checked in mysql-5.5-innodb.
[13 Nov 2010 16:26] Bugs System
Pushed into mysql-trunk 5.6.99-m5 (revid:alexander.nozdrin@oracle.com-20101113155825-czmva9kg4n31anmu) (version source revid:alexander.nozdrin@oracle.com-20101113152450-2zzcm50e7i4j35v7) (merge vers: 5.6.1-m4) (pib:21)
[13 Nov 2010 16:41] Bugs System
Pushed into mysql-next-mr (revid:alexander.nozdrin@oracle.com-20101113160336-atmtmfb3mzm4pz4i) (version source revid:alexander.nozdrin@oracle.com-20101113152540-gxro4g0v29l27f5x) (pib:21)
[16 Dec 2010 22:34] Bugs System
Pushed into mysql-5.5 5.5.9 (revid:jonathan.perkin@oracle.com-20101216101358-fyzr1epq95a3yett) (version source revid:jonathan.perkin@oracle.com-20101216101358-fyzr1epq95a3yett) (merge vers: 5.5.9) (pib:24)