Nikolay Samofatov wrote about his Large Iron production systems that he maintains :

We run Firebird to power larger systems (for 12 government agencies and 3 banks).

It has approximately 100000 end users multiplexed through 2500 (max) pooled connections.

Here is the snapshot of nearly idle system at night:

top - 03:20:39 up 10 days, 8:39, 7 users, load average: 2.08, 1.87, 2.15 Tasks: 1732 total, 1 running, 1730 sleeping, 1 stopped, 0 zombie Cpu(s): 11.9%us, 4.0%sy, 0.0%ni, 83.5%id, 0.0%wa, 0.0%hi, 0.6%si, 0.0%st Mem: 529177288k total, 378587600k used, 150589688k free, 761532k buffers Swap: 1073741816k total, 130612k used, 1073611204k free, 333281232k cached [root mvv bin]# ps aux | grep -c rdb_inet_server 719

Database is on a small FusionIO drive:

mount: /dev/fiob on /mnt/db type ext2 (rw,noatime) df -h: /dev/fiob 587G 423G 135G 76% /mnt/db

Also later he mentions that he uses 2TB of RAM machines