question about the _SPI_save_plan() and plan cache

Hi,
 It seems postgres cache the plan under CacheMemoryContext during the 
plpgsql executing.
If there is a function with lots of variables and every one of them got a 
default value,
postgres will allocate lots of memory for caching the default value plan(we 
have to run
the function at least once). Once we DROP the function, the memory consumed 
by the plan
will be leak. The same thing for the compiled function 
structure(PLpgSQL_function).
 Is this an oldest known question?


Thanks,
Tao Ma