Re: Calling Java from psql (was Re: requesting help)

Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
> A James Lewis writes:
>> Before I go investigating this, is it possible to trigger an arbitrary
>> program from the SQL, say a shell script?

> At the lowest level, you can generally do anything a C program can do.
> Writing the equivalent of system() in SQL should be rather trivial.

I'm generally pretty suspicious of any system design that requires
calling outside programs from an SQL function. The problem is that
this fundamentally breaks transactional semantics: if the transaction
is rolled back after the function call, its effects inside the database
disappear ... but there's no way to roll back whatever the outside
program did. Now you have a consistency problem.

I'd suggest thinking hard about how to restructure your system design
so that you do not need this capability. Yes, it'd be easy to implement,
but that doesn't make it a good idea.

regards, tom lane