Bug #28186 SHOW ENGINE INNODB MUTEX documentation is incomplete
Submitted: 1 May 2007 20:50 Modified: 13 Sep 2007 19:17
Reporter: Baron Schwartz (Basic Quality Contributor) Email Updates:
Status: Closed Impact on me:
Category:MySQL Server: Documentation Severity:S3 (Non-critical)
Version:5.1.17-beta OS:Any
Assigned to: Paul DuBois CPU Architecture:Any
Tags: Docs, innodb, mutex, show

[1 May 2007 20:50] Baron Schwartz
The documentation for SHOW ENGINE INNODB MUTEX and SHOW MUTEX STATUS has a few minor issues.  (SHOW MUTEX STATUS is the older form of the command).

There appear to be duplicate rows in the results of both commands.  For instance, in SHOW MUTEX STATUS, the same mutex is printed out, but with different counts.  I have a feeling this is because these numbers are from different threads or something like that, but I don't know.

Also, there is a typo in http://dev.mysql.com/doc/refman/5.0/en/show-mutex-status.html.  It says

"OS_waits_time  os_wait_times indicates the amount of time..."

I think the 's' at the end of 'os_wait_times' needs to be removed and placed after 'wait'.  There is no 'os_wait_times' column in the result.

How to repeat:
Documentation bug

Suggested fix:
Could you please explain the duplicate rows in the results?
[1 May 2007 21:15] MySQL Verification Team
Thank you for the bug report.
[2 May 2007 0:55] Baron Schwartz
I just looked at a server we recently upgraded to 5.0.38 and it looks to me like the behavior of SHOW MUTEX STATUS is not what is documented.  It looks like the same results you get from SHOW ENGINE INNODB MUTEXES in 5.1.
[2 May 2007 1:01] Baron Schwartz
Whoops!  I am wrong about the last comment.  The columns in 5.0.38 are not the same as in 5.1.  They are titled  file, line, os_waits.

(I got so many rows in the result that I could not see the headers).
[6 Jul 2007 0:15] Baron Schwartz
It's not one of my clearest bug reports is it.  My apologies.

I think the documentation should explain the (three?  more?) different formats, note when they changed, and give a sample of output for each.  An explanation of why there are duplicate rows and what they mean would be especially helpful for me (I would like to aggregate the rows with a client-side script but am unsure if the result will be meaningful).  There is also a slight typo with the column names (os_wait_times).
[13 Sep 2007 19:17] Paul DuBois
Thank you for your bug report. This issue has been addressed in the documentation. The updated documentation will appear on our website shortly, and will be included in the next release of the relevant products.

The variant output formats now are documented here:


The variants differ by version number, and according to whether the
UNIV_DEBUG symbol was defined when MySQL was compiled. If this
symbol is not compiled, fewer output columns are displayed, and
this is what causes the apparently duplicated rows in output: With
fewer output columns, there is less information to distinguish one
mutex from another.