Firebird 3 SuperServer performance limitation over Classic

[Fabiano SCI]

Hello.

Six months ago we migrated all our customers from Firebird 2.5.7 Classic to Firebird 3.0.6 SuperServer all on Windows.

All was great until one customer experience intermittent slow downs. This customer have 190 users running, 286Gb database (just one) on a Windows Server 2012 with 128Gb of RAM, 32 2,4Gb processors and a SSD drive (on a DELL Perc H730 controller). During the slow down time, NEVER the Server became 100% full. Maximum CPU usage was ~40%, disk use <10% and memory usage < 40%. The server is dedicated to this database. The Super Server was optimized with lock_hash_slots of 65521 and 50000 database page caches. 

After 3 months of problem solving we discovered that the Super Server architecture experiente a gradual slow down when there is more than a 11000 SQL executed per second. Then, we switch the Super Server to Classic again and the performance problem was solved!

So I ask: There really a limit on how much concurrent SQL the Super Server can handle? If this limit exists it was raised on Firebird 4?