Re: When deleting the plpgsql function, release the CachedPlan of the function

It seems not an easy task. And here is my new work of such task.
The main idea is register a sys cache callback in cached_function_compile
when not registered. So it will effect for all SPL.
And also introduce a new hash table to track the function for cache inval
callback. The procedure in callback to lookup for a function will be:
hashvalue
     |
     v
[lookup func_key_hashtable]
     |
     v
  func_key
     |
    v
[lookup func_hashtable]
    |
    v
 function

But still remain lots of work to consider. As we don't know what's the real
operation of this invalidation, that's may cause unnecessary deletion. e.g.

postgres=# create or replace function strtest() returns text as $$
postgres$# begin
postgres$#   raise notice 'foo\\bar\041baz';
postgres$#   return 'foo\\bar\041baz';
postgres$# end
postgres$# $$ language plpgsql;
WARNING:  nonstandard use of \\ in a string literal
LINE 3:   raise notice 'foo\\bar\041baz';
                       ^
HINT:  Use the escape string syntax for backslashes, e.g., E'\\'.
WARNING:  nonstandard use of \\ in a string literal
LINE 4:   return 'foo\\bar\041baz';
                 ^
HINT:  Use the escape string syntax for backslashes, e.g., E'\\'.
WARNING:  nonstandard use of \\ in a string literal
LINE 4:   return 'foo\\bar\041baz';
                 ^
HINT:  Use the escape string syntax for backslashes, e.g., E'\\'.
CREATE FUNCTION
postgres=# select strtest();
WARNING:  nonstandard use of \\ in a string literal           <--- redundant warning
HINT:  Use the escape string syntax for backslashes, e.g., E'\\'.
WARNING:  nonstandard use of \\ in a string literal
HINT:  Use the escape string syntax for backslashes, e.g., E'\\'.
NOTICE:  foo\bar!baz
WARNING:  nonstandard use of \\ in a string literal
LINE 1: 'foo\\bar\041baz'
        ^
HINT:  Use the escape string syntax for backslashes, e.g., E'\\'.
QUERY:  'foo\\bar\041baz'
   strtest   
-------------
 foo\bar!baz
(1 row)

the function works no error, but cause deplicate warning message. i'm still working on this...