Re: [Maria-developers] MariaDB mutex contention

Hi, Pavel! On Aug 20, Pavel Ivanov wrote:

On Tue, Aug 20, 2013 at 1:09 AM, Sergei Golubchik wrote:

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On Aug 19, Pavel Ivanov wrote:

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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. Regards, Sergei