On the page Optimize and Scale Piwik - Analytics Platform - Piwik
Under the heading “Meet other Piwik Power users & Share your experience” there are two broken links to the forum
Seems to be fixed in the meantime.
Looks like they’ve removed links to the forum and have put links to paid support in their place.
I just checked and those links don’t seem to work for me either. Looks like they might be outdated or moved hopefully the team can update them soon.
I’ve noticed those broken links too - it’s a bit frustrating when you’re trying to tune the database and the trail goes cold. I found that searching the Matomo FAQ for ‘performance’ usually brings up the most recent advice that used to be in those forum threads.