Apache (and mod_perl) was thread safe by being multi-process, single threaded. You were always limited by how many perl interpreters could fit in RAM simultaneously. Then came the era of the Java app server (Weblogic and WebSphere).

Everyone has mostly forgotten AOLserver (and TCL!). Almost everyone of that generation was influenced to use a RDBMS as a backend by Philip and Alex's Guide to Web Publishing which came out in 1998.[0] Although I never actually met anyone who used AOLserver itself! Everyone took the idea and implemented it in ASP or perl, until the world succumbed to EJBs.

[0] https://philip.greenspun.com/panda/

That was also the era when DBMS locking was iffy, so competing inserts/updates would happen once sites got too busy, and everyone was encouraged to turn off transactions (or, on MySQL, just use MyISAM instead of InnoDB) and put it on XFS or even tempfs for speed.

So many websites I remember came back up with "the last two weeks of posts are gone, sorry" or just shut down for good because it was all too corrupted to fix, and so were the backups, if they had any.

I used AOLserver with OpenACS, https://openacs.org/ . AOLserver was apparently more optimized than Apache (at the time, at least).

My manager even had us (early 2000s) take a one-week(?) bootcamp at Ars Digita HQ in Boston. Though about the only thing I remember from it was the fancy aeron chairs.

AOLserver was a joy. I was able to speak about it at the O'Reilly OSCON in 2000 or so.