1. A method comprising: receiving, by a database system, a query statement; forming a runtime plan tree in accordance with the query statement; and traversing the runtime plan tree, comprising: determining whether a function node of the runtime plan tree is qualified for just-in-time (JIT) compilation, and upon determining that the function node is a qualified for JIT compilation: producing a string key in accordance with a function of the function node, and determining whether a compiled object corresponding to the string key is stored in a compiled object cache.