Code review comment for lp:~ebergen/maria/mysqld_safe_fix

On Mon, Feb 25, 2013 at 5:40 AM, Michael Widenius <email address hidden> wrote:
>
> Hi!
>
>>>>>> "Eric" == Eric Bergen <email address hidden> writes:
>
> Eric> Eric Bergen has proposed merging lp:~ebergen/maria/mysqld_safe_fix into lp:maria.
> Eric> Requested reviews:
> Eric> Maria-captains (maria-captains)
>
> Eric> For more details, see:
> Eric> https://code.launchpad.net/~ebergen/maria/mysqld_safe_fix/+merge/150210
>
> Eric> This contains two changes to mysqld_safe.sh
>
> Eric> The first adds an option --crash-script for a script to call when mysqld crashes. This can be useful for gathering extra information, notifying operators, or triggering a failover when using HA.
>
> This part is ok.
>
> Eric> The second removes a rm command that deleted the sock file. This could delete the sock file for another instance when MYSQL_UNIX_PORT environment variable is set.
>
> What you removed was:
>
> - rm -f $safe_mysql_unix_port "$pid_file" # Some extra safety
>
> You can't remove the delation of "$pid_file";
>
> Without that mysqld_safe.sh will not properly.

mysqld_safe does a proper pid file check earlier and fails with an
error message if the stale pid file can't be cleaned up. The server
also opens the pid file with O_TRUNC so it will also get cleaned up.

>
> There is one problem with not removing the socket port:
> - If you don't do that, mysqld will not restart from a crash as the
> old socket file will stop the server from starting.

The server does a blind unlink call on the socket file prior to
creating a new one so it won't fail on a stale socket file.

>
> Eric> This caused problems for me because I use a non-standard installation. Upgrading the MariaDB-Server rpm would delete the sock file from my relocated mysqld leaving it orphaned.
>
> If you specify "socket" in your my.cnf, this should never go wrong.
>
> If you don't specify "socket" and you have another MySQL server
> running, your new server should not start as the socket file would be
> conflicting.
>
> Can you please describe in litte more detail how your installation
> looked like where you got conflicting socket names?

This happens when relocating a mysql instance from the default paths
provided in rpms. It is fairly common to relocate mysql for developers
to use a server with their own instances.

The problem showed up for me when a user was setting
MYSQL_UNIX_PORT=/home/user/path/to/relocated/mysql.sock and then
upgraded the MariaDB-Server package. The mysqld_safe executed during
the rpm installation deleted the relocated mysql_unix_port while
running the installation.

The real fix from my end is to manage MYSQL_UNIX_PORT better or to get
rid of it in favor of ~/.my.cnf. I found it odd that there was a line
with the comment "Some extra safety" implying that it didn't fix any
known issue. It was also doing cleanup that was harmful in my case and
not necessary.

>
> I will wait with applying your crash-script option until we find a
> solution for the above.
>
> Regards,
> Monty
>
> --
> https://code.launchpad.net/~ebergen/maria/mysqld_safe_fix/+merge/150210
> You are the owner of lp:~ebergen/maria/mysqld_safe_fix.

--
Eric Bergen
<email address hidden>
http://www.ebergen.net