The documentation says that a support function should have a signature "supportfn(internal) returns internal”, but doesn’t say which (if any) annotations should be provided. IMMUTABLE? PARALLEL SAFE? STRICT? None? All?
Variable SupportRequestCost is very exciting, but given that variable cost is usually driven by the complexity of arguments, what kind of argument is the SupportRequestCost call fed during the planning stage? Constant arguments are pretty straight forward, but what gets sent in when a column is one (or all) of the arguments?