Re: libpq lo_open errors when first action in connection

"Greg Sabino Mullane" <greg@turnstep.com> writes:
> I'm having some problems with lo_open inside of DBD::Pg (which
> uses libpq) and need help in debugging the problem.

lo_open doesn't work unless inside a transaction block (and even
if it did work, the result would be useless to you).

I believe the reason for the -1 result is this code inside libpq's
lo_open:
       /* have to do this to reset offset in shared fd cache */       /* but only if fd is valid */       if (fd >= 0
&&lo_lseek(conn, fd, 0L, SEEK_SET) < 0)           return -1;
 

Since you forgot to start a transaction block, the results of the
backend lo_open call are already dead and the lo_lseek fails withERROR:  invalid large-object descriptor: 0

This looks rather considerably like a hack to compensate for a very
long-gone bug ... can anyone see a reason not to take it out?
Of course taking it out wouldn't improve Greg's results much, since
he'd still get a failure at the next LO operation, but this sure
looks like it's incurring a useless network round trip...
        regards, tom lane