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Re: MariaDB mutex contention


Hi, Roberto!

On Aug 19, Roberto Spadim wrote:
> hummm some doubts since i never used/write an audit plugin...
> the lock_plugin of query response time, is a audit plugin + a
> information schema plugin right?

query response time is a pair of plugins, yes. one information schema
plugin and one audit plugin.

> he audit plugin is 'called' at query start and query end? or there's
> more locks used?

An audit plugin may be called many times per query.  But it's locked
only once, at the query start, then it's cached in the THD.

> when used the locked is used in what case? to lock the UNINSTALL PLUGIN command?
> should be nice a flow about this plugin locks

LOCK_plugin is used to protect the list of loaded plugins and the hash
of plugin names. One takes it to make sure the plugin can not be
unloaded by another thread at this very moment.

Statically compiled plugins cannot be unloaded, and they don't take
LOCK_plugin or do any reference counting at all.