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Re: Semaphore hangs


On 08/12/16 08:51, Jon Foster wrote:
> We are having trouble with MariaDB hanging due to a "semaphore wait". We
> then have to shut MariaDB down as it typically won't recover, unless it
> restarts itself, which happens if we wait long enough. But if its gone
> on long enough MariaDB won't even shutdown, it hangs indefinitely
> waiting for some other internal service. I don't remember the exact name
> and we've been fast enough I haven't seen it in a while.
> We've had the database on two completely different servers and still see
> the problem. Both servers were bought new for this project and are a
> year or less old. They are running all SSD drives, Debian 7 64bit with
> MariaDB 10.1 from the MariaDB APT repository.
> Since the XtraDB engine was usually mentioned in the logged messages we
> switched back to the Oracle InnoDB engine. Although this seems to have
> reduced the frequency it didn't fix it.
> Can anyone give some advice on fixing this. It really seams like a bug
> in MariaDB. I'll try to provide any needed info.
> TIA - Jon

Needed info:
* exact MariaDB version 10.1.X
* mariadb configuration
* what is the entire mysql log from the startup until the "semaphore wait"
* how are you determining "semaphore wait"
* is a SHOW FULL PROCESS LIST possible? if so contents?
* when in a stalled state run on a commmand line (with gdb installed)
gdb --batch --eval-command="thread apply all bt" program $(pidof mysqld)