Problems with MySQL since upgrade

[Richard Morse]

On Aug 1, 2006, at 9:24 AM, Richard Morse wrote:

> Hi!  I recently updated MySQL to version 5.0.22 using the ports  
> system (portupgrade -r -R mysql-\*).  Previous to this, MySQL was  
> behaving perfectly normally.  Since the upgrade, I have found that  
> every so often -- sometimes two or three times a day, sometimes  
> every other day, but no more often than that -- one of the  
> databases MySQL is hosting starts misbehaving, MySQL starts  
> climbing in processor usage, and I have to restart MySQL to  
> recover.  By "misbehaving", I mean that some subset of queries to  
> this database start not returning -- they take forever.  By  
> climbing in processor usage, I mean that my load averages, which  
> normally sit around 0, start going up to 3, 5, even 7.
>
> - How can I determine what query it is that is causing this to  
> happen?  I have turned on the log files by adding the following  
> line to /etc/rc.conf:

Hi!  Since this time, I have, I think, found what query is causing  
the problem:

SELECT u.*, s.* FROM users u INNER JOIN sessions s ON u.uid = s.uid  
WHERE s.sid = "d9fe25949f79f2c767a0d237b4fdf841" AND u.status < 3  
LIMIT 0, 1

How can I determine _why_ this is causing MySQL to hang/enter some  
kind of infinite loop?

Thanks,
Ricky