kmf

Tried it all before, but the best combo for me is what I'm using at this moment too. Sessions being MEMORY STILL causes tablelocks, even though the table is fast, it takes time for the script to finish using it and releasing it. (i've tried memory-tables on version 1.3 of IPB. That's years ago. And I merely had 500 people online at the same time. Now with 10 times that amount, I doubt memory tables scales correctly) Apache2 with modPHP works fine for the webservers, as long as eaccelerator is there. I use lighttpd for the static files on another server. And sphinx for searches. ATM there is just no need for me to experiment further and lose capabilities of apache in exchange for speed from lighttpd. The usage of various options is all a matter of balance.

eaccelerator on itself is mainly used for pre-compiled php. But if you install it with the "shared-memory" option, you can let it work like memcache too. Only downside is, as far as I know, it only works on the local server. Whereas memcache allows you to offload all cache to another server. Upside is, faster PHP-interpreting and auto file/memory caching rotation. IPB is using partial caching. Meaning it won't cache direct results, but parsed, sorted and prepared data. Something I prefer and make use off myself too. So it doesn't really matter much what caching you use, if you know the advantage of the one over the other. I'm pretty sure IPB does not support MULTIPLE caches though... otherwise you could use a combo of eaccelerator and memcache.

I'm using eaccelerator for caching. It's a form of memcache and filecache. That's because I'm at a budget and can't afford a server with a lot of memory for memcache. And eaccelerator works great too.

It's running on 3 dedicated servers. 2 webservers loadbalanced and 1 database server. The webservers are using eaccelerator. Gzip was disabled and I used mod_deflate to zip all non-img static files. We just upgraded to ipb3 from ipb2, so we're still testing things out. As it seems that ipb3 is causing twice as much load. Also, for search we used xapian and sphinx. The database is using innodb for the large and fast-update tables like posts, members and session.

I guess you need to prepare a server for memcache or other caching too. This forum has 6000 users at the same time and it's pretty snappy. http://asianfanatics.net/forum/