rsdb/cua/buffersize is a SAP Parameter attribute which is used to control CUA Buffer Size information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
Specifies the size of the CUA puffer. The CUA buffer holds objects
from the GUI interface, such as menus, pushbuttons, and so on.
In the data base, these objects are held in tables D342L and D345T.
Small systems
1500 - 2500 KB
Medium-sized systems
2500 - 3000 KB
Large Systems
3000 - 6000 KB.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.