maria-developers team mailing list archive

[Jeremy Cole <jeremycole@xxxxxxxxxx>]

It would seemingly be a reasonable idea to have an option to lock certain
plugins in a "permanent" loaded state, so that they cannot be unloaded at
runtime, but all of that per-entry locking can be avoided with e.g. if
(!plugin->permanent) checks for the lock/unlock. Then, a server restart
would be required to unload the plugin.

Regards,

Jeremy


On Mon, Aug 19, 2013 at 10:44 AM, Pavel Ivanov <pivanof@xxxxxxxxxx> wrote:

> No, it's not reasonable for semi-sync to lock/unlock LOCK_plugin. It's
> plugin infrastructure that does that.
>
> I've actually was terrified to learn that each call into semi-sync
> plugin is surrounded with pthread_rwlock_rdlock/pthread_rwlock_unlock
> (which is not cheap I believe). And also for each such call it
> "locks"/"unlocks" the semi-sync plugin. And although "locking" plugin
> avoids locking LOCK_plugin when plugin is linked statically,
> "unlocking" doesn't do that. And with all that calls into semi-sync
> plugin happen I believe twice for each COMMIT and twice for each
> binlog event sent to each slave.
> I'd say that's a big performance hog...
>
> On Mon, Aug 19, 2013 at 8:27 AM, MARK CALLAGHAN <mdcallag@xxxxxxxxx>
> wrote:
> > Is it reasonable for semi-sync to need to lock/unlock LOCK_plugin that
> > frequently? The plugin architecture, like most of the rest of MySQL,
> wasn't
> > described to people on the outside (like me).
> >
> >
> > On Mon, Aug 19, 2013 at 6:32 AM, Pavel Ivanov <pivanof@xxxxxxxxxx>
> wrote:
> >>
> >> On Mon, Aug 19, 2013 at 5:17 AM, Roberto Spadim <roberto@xxxxxxxxxxxxx>
> >> wrote:
> >> > hi!
> >> >
> >> >> Another plugin that should be disabled is QUERY_RESPONSE_TIME. It has
> >> >> quite
> >> >> some impact on LOCK_plugin:
> >> >>
> >> >> -DWITH_QUERY_RESPONSE_TIME=1
> >> >>
> >> >>
> >> >>
> +-----------------------------------------+------------+-----------------+
> >> >> | event_name                              | count_star |
> sum_timer_wait
> >> >> |
> >> >>
> >> >>
> +-----------------------------------------+------------+-----------------+
> >> >> | wait/synch/mutex/sql/LOCK_open          |    2743723 |
> >> >> 160451183703111 |
> >> >> | wait/synch/mutex/mysys/THR_LOCK::mutex  |    2743651 |
> >> >> 19122327109683 |
> >> >> | wait/synch/mutex/sql/LOCK_plugin        |    3135747 |
> >> >> 18611700478728 |
> >> >> | wait/synch/rwlock/sql/LOCK_tdc          |    1356784 |
> >> >> 1360918935810 |
> >> >>
> >> >> -DWITHOUT_QUERY_RESPONSE_TIME=1
> >> >>
> >> >> completely removes LOCK_plugin from the top 20 list. This is also
> >> >> considered
> >> >> a bug as the plugin API should be lightweight.
> >> >>
> >> >
> >> > Should the
> >> > "SET GLOBAL query_response_time_stats=0"
> >> > solve this contention problem? or the LOCK_plugin is called always,
> >> > doesn't matter if it's "disabled" or not?
> >>
> >> If it's implemented the same way as semisync plugins (and it should be
> >> implemented like that) then LOCK_plugin is locked even when plugin's
> >> functionality disabled, because it gets disabled using plugin-specific
> >> variable which can be checked only inside the plugin code.
> >>
> >>
> >> Pavel
> >>
> >> _______________________________________________
> >> Mailing list: https://launchpad.net/~maria-developers
> >> Post to     : maria-developers@xxxxxxxxxxxxxxxxxxx
> >> Unsubscribe : https://launchpad.net/~maria-developers
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> >
> >
> >
> >
> > --
> > Mark Callaghan
> > mdcallag@xxxxxxxxx
>
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