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Re: MariaDB mutex contention


Hi, Pavel!

On Aug 20, Pavel Ivanov wrote:
> On Tue, Aug 20, 2013 at 1:09 AM, Sergei Golubchik <serg@xxxxxxxxxxx> wrote:
> > On Aug 19, Pavel Ivanov 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.
> >
> Sure, but macro FOREACH_OBSERVER inside rpl_handler.cc doesn't use
> this function. It uses plugin_unlock_list() which always locks
> LOCK_plugin.
> BTW, MariaDB still supports compiling semi-sync plugins dynamically,
> but it seems that it doesn't do anything against unloading semi-sync
> plugins in the middle of transactions. Did anyone think about this?

Judging from the replication plugin API - I don't think so.

But if it adds that much overhead, I suppose we'll need to fix it.
Then we fix the unloading too.


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