Bug #35661 legacy and incorrect memory formula and message written to error log after crash
Submitted: 28 Mar 2008 22:19 Modified: 10 Oct 2018 12:09
Reporter: Shane Bester (Platinum Quality Contributor) Email Updates:
Status: Duplicate Impact on me:
None 
Category:MySQL Server: Errors Severity:S3 (Non-critical)
Version:4.1, 5.0, 5.1, 5.5 OS:Any
Assigned to: CPU Architecture:Any

[28 Mar 2008 22:19] Shane Bester 
Description:
When the mysqld server crashes, it writes this to the error log:

---
It is possible that mysqld could use up to
key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 59968 K
bytes of memory
Hope that's ok; if not, decrease some variables in the equation.
---

This formula is misleading and wrong.  It doesn't take into account many variables.

Furthermore, if mysqld runs low on memory, OOM killer can kill the process and this error will not be shown anyway.  These days, memory allocation failures are handled better, by printing out of memory errors, not by crashing.

How to repeat:
Read the code or an error log.

Suggested fix:
Remove it or correct it.  How about stating what the *actual* memory usage was according to the OS, at the time of the crash?
[31 Mar 2008 17:51] Sveta Smirnova 
Thank you for the reasonable feature request.
[8 Sep 2008 11:09] MySQL Verification Team 
In addition, i would like to see the number of malloc's that failed during the server's uptime.   Can we print this is to the crash log?
[18 Feb 2009 12:34] MySQL Verification Team 
http://www.mysqlperformanceblog.com/2009/02/12/how-much-memory-can-mysql-use-in-the-worst-...
[18 May 2010 7:39] MySQL Verification Team 
impacts all users who are conned into believing wrong.
just remove the incorrect formula and be done with it.
[28 Jul 2010 9:58] Roel Van de Paar 
Bug #55594 (referring to InnoDB variables) was marked as a duplicate of this one.
[29 Jul 2010 2:09] Roel Van de Paar 
Note that part of the InnoDB information is already available: it is shown in SHOW ENGINE INNODB STATUS:

----------------------
BUFFER POOL AND MEMORY
----------------------
Total memory allocated 138412032; in additional pool allocated 0
Dictionary memory allocated 39020
Buffer pool size   8192
Free buffers       1684

Maybe the code for this can be re-used/referenced.
[29 Nov 2010 17:20] Sasha Pachev 
Yes, the formula is from back before the InnoDB days when those variables were often the primary cause of large allocations. Nowadays it is rather irrelevant. mysqld could still use up to that much memory, but it is likely to be using more.
[21 Aug 2013 20:05] MySQL Verification Team 
probably a duplicate of
http://bugs.mysql.com/bug.php?id=1694
[22 Jan 2015 2:57] Roel Van de Paar 
http://bugs.mysql.com/?id=75536
[10 Oct 2018 12:10] Steinar Gunderson 
Was filed and fixed as #92731 / #28773322.