External functions/languages and transactions

Dear All,

I've been working (a little) on external functions and laguages recently, and was wondering how PG handles updates to
librariesand/or stored procedures in the context of transactions. This is probably most relevant to Perl, but really
appliesto any external function.
 

If:

1. user A starts a TX, and calls a user defined function in userlib.so, 
2. user B changes, recompiles, and reloads the shared library
3. user A calls the same function within the same TX.

Does PG prevent the 'load' command by user B (via locking)?
Does user A get a different result?
Does user A's backend not load the new module until after a commit?

In the extreme case this is obvoiusly totally outside the control of PostgreSQL, but in the case of Perl, which
includesall sorts of external files, should the implementor of PL/Perl be careful to NOT update already loaded module?
Orto update them ASAP?
 

This is probably too unlikely to worry about, but I am (academically) interested...


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