There used to be lots of problems handling more than 400 simultaneous users, but after a DB upgrade to Firebird v2.5 Alpha 1 things really look different.
Previously the DB machine (Dualcore) had one of the CPU’s running at 100% and the other not doing much (FB was Superserver) but after the switch the TOTAL CPU now ranges between 10% and 50% on the DB machine. At the same time the WebServer CPU load also decreased and is constantly under 60% where it used to be over 95% all the time!
So by just switching to the new DB engine a tremendous performance gain was achieved! Also a lot less errors are reported to the PHP error logs. The ones still coming are a deadlocks, but around 30 / 24h which is a lot less than it used to be!
To the Firebird team I want to say “THANK YOU for making a great database engine” !