We're running Simple Login Log on a WordPress Multisite, network activated - and only started seeing this problem in the last 2 months or so...
We've been debugging a significant performance issue on our server for a while... and after a lot of digging, we isolated it to a full table retrieval query coming from Simple Login Log.
It seems this query below is hitting the database for every page-view of wp-login.php - not for attempted login, but litearlly just going to wp-login.php triggers it:
SELECT * FROM wp_simple_login_log
I'm not sure off hand what other wordpress pages generate might also trigger query... but I was able to verify it happens with wp-login.php
I would thing this query should only run when one clicks on the WP admin -> Users -> Login Log menu, right?
But for some reason it's being triggered in other areas as well and basically bringing down our MySQL and the server along with it.
As soon as I disabled the Simple Login Log plugin, our MySQL became almost dormant lol, the performance issues disappeared completely.
But before that, I could do "mysql> show processlist;" repeatedly over and over and always see a couple of these queries - in spite of how quickly MySQL processes and completes the queries.
But we'd really like to re-enable it! :-)
Could you please check this out and see what the fix may be...
This is a high traffic site and we don't prune the login log table, as we keep those records. This might not have been noticed on a low traffic site or a site where the records are purged regularly. :-)
We only started seeing these performance issues some weeks ago, maybe 2 months. So maybe a bug snuck into the latest update or two?