Performance issues

Hi,

We are experiencing inconsistent performance issues on our large Multisite installation. We have database connection spikes every week or so. The database spike typically last several hours then return to normal. We are having trouble finding the exact cause. We've tried installing Query Monitor as well as WP Cron but the results are inconclusive.

Does anyone know a good tool to help identify the exact cause of issues like this?

Thank you,

Ben