Possible Threading problem with -CURRENT / MySQL?

Julian Elischer julian at elischer.org
Mon Jun 14 18:15:40 GMT 2004

On Mon, 14 Jun 2004, Lasse Laursen wrote:

> MySQL 4.0.20 was compiled with --without-libwrap (libwrapper seems to be
> broken) and WITH_PROC_SCOPE_PTH set to yes.
> WE use the SCHED_ULE, and:
> # Memory options
> options         MAXDSIZ="(1536*1024*1024)"
> options         MAXSSIZ="(1024*1024*1024)"
> options         DFLDSIZ="(1536*1024*1024)"
> The server runs fine until a single thread/query suddenly locks up the
> entire MySQL daemon. After that all queries are just queued and a restart of
> the daemon is needed to unlock the system. The system itself is stable
> enough as far as I can see. 'top' reports a lot of locks (*Giant) so I
> assume that it's some weird problem with the threading? We used to use
> FreeBSD on non-SMP machines without any problems.
> I have tried with linux threads as well but the same problem occurs.

This does suggest a bug in MySQL, but let's investigate anyhow..

> Have anyone experienced any similar problems and found a solution to this
> rather weird problem?
> Feel free to request any further information about the system/setup and I
> will do my best to provide it to the list.

the output of "ps -alxH might be useful.

 do you have teh kernel debugger compiled into the kernel?
(option DDB)

if so..
note the PID of the process
sysctl debug.enter_debugger=ddb
[you are now in the debugger]
[note the Thread address of the threads that seem to be blocking things]
(I may ask for specific threads after seeing the 'ps' output)

show thread {address}

to get a stack backtrace of those threads.

if possible use a serial console to do all this.. That way you can log
it all.

to make a serial console, connect 2 machines com1 by a null-modem cable.

on the other machine do:
tip com1

on the SQL machine add
into /boot/loader.conf and reboot

all console out put from teh boot-loader-on will now go to teh serial
port and appear in teh 'tip' output. (which is being logged by the
'script' command).


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