Bitfinex is not a financial services business run by competent, experienced professionals.
Bitfinex is not built from the ground up on sound principles of engineering.
Bitfinex was copied from the leaked bitcoinica codebase, a Ruby-on-Rails app written by then 16 year old Ryan Zhou.
Saying "they reverse-engineered it" would be overly charitable.
Bitfinex was released within some weeks of the Bitcoinica source code leak.
The codebase was copied from a defunct, thrice robbed company.
That code is not capable of keeping the database consistent at peak loads.
That code is not scalable. That code was not, and is not correct.
Not correct according to specification. (Which doesn't exist.)
Not correct according to expectation. (The business logic of the exchange is broken.)
This becomes evident as the load on their server approaches capacity.
Everything goes to shit. Time and time again.
Their database stuff seems limited to concurrent reads, but single threaded writes.
It is a product of inspired design, not engineering.
It is very far from being remotely acceptable for a financial exchange.
But at least they have been making money since day one.
(Because they had essentially no development costs, starting out.)
There is a good story here, waiting to be written by some investigative journalist.
Perhaps we will have to wait for some catastrophe before that happens.

Bitfinex was copied from the leaked bitcoinica codebase, a Ruby-on-Rails app written by then 16 year old Ryan Zhou.
This alone is a reason not to use it, I still have domains stranded in that gobshites domain registrar (nameterrific) that was first to accept bitcoin
I hear he is now running coinjar in Australia, pitty the fools who use that now