Re: Warning about mysqld's behaviour

[Charlie Brady <charlieb@budge.apana.org.au>]

On Thu, 14 Apr 2005, Alex Efros wrote:

> I use this ./run with MySQL 4.0.x. It allow me control mysql using runsvctrl:
> ---cut---
> #!/bin/bash
> exec </dev/null >/dev/null 2>/dev/null
> SHUTPASS="HERE_IS_ME_PASSWORD"
> trap "mysqladmin -u shutdown -p$SHUTPASS shutdown" 0
> trap 'exit 2' 1 2 3 15
> mysqld_safe --default-character-set=koi8_ru & wait

The reason that I use runsvctrl is that I believe that (with runit) I can 
provide a better "mysqld_safe" than the mysql packagers can. Or, to put it 
another way, mysqld_safe (called safe_mysqld in mysql-3) is just an 
attempt to do in a shell script (most of) what runit already does more 
simply and reliably.

One thing that safe_mysqld does which a runit run script won't do is 
attempt to detect hung processes and then send them a -9 signal - but I 
think that's a very suspect thing to do.

Since safe_mysqld depends on pid files and parsing the oputput of the ps 
command, I'm sure that it's full of potential race conditions.

> ---cut---
> (I've special user "shutdown" with only permission to shutdown server
> because I dislike use "root" user and put it password in this script.)
>
> I've switched from sending TERM to mysqld to using "mysqladmin shutdown"
> some time ago because on very busy server sending TERM sometimes result
> in damaging database. There was number of cases when after reboot with
> "init 6" I found database crashed. :(

safe_mysqld starts mysqld with --skip-locking - perhaps that contributed 
to your database corruption.

I prefer to follow Einstein's directive - make it as simple as possible - 
but no simpler.

---
Charlie