Languages descended from APL are very popular among the financial engineering set.
Nowadays it's in a window, but it looks the same. I don't know if they still use J, or K, but anyway not in real-time. That happens on FPGAs in a rack where traders once roamed.
But while APL cannot be said to be very popular, the most popular "time-series database" used in finance is published by APL fananics.
The specialized time-series database lost much of its reason to exist when disk seek times went to zero. Nowadays you stage onto an SSD, and spool to rotating storage later, if at all.
First Derivatives’ revenue last FY was ~200m and their pre-tax profit is ~17m. To say that they are unaccountably popular on the Street is quite an overstatement.