Re: [EXTERNAL] Re: Support load balancing in libpq

As far as I can tell this is ready for committer feedback now btw. I'd
really like to get this into PG16.

> It hadn't been my intention to block the patch on it, sorry. Just
> registering a preference.

No problem. I hadn't looked into the shared PRNG solution closely
enough to determine if I thought it was better or not. Now that I
implemented an initial version I personally don't think it brings
enough advantages to warrant the added complexity. I definitely
don't think it's required for this patch, if needed this change can
always be done later without negative user impact afaict. And the
connection local PRNG works well enough to bring advantages.

> my
> assumption was that you could use the existing pglock_thread() to
> handle it, since it didn't seem like the additional contention would
> hurt too much.

That definitely would have been the easier approach and I considered
it. But the purpose of pglock_thread seemed so different from this lock
that it felt weird to combine the two. Another reason I refactored the lock
code is that it would be probably be necessary for a future round-robin
load balancing, which would require sharing state between different
connections.

> > And my thought was that the one-time
> > initialization could be moved to a place that doesn't need to know the
> > connection options at all, to make it easier to reason about the
> > architecture. Say, next to the WSAStartup machinery.

That's an interesting thought, but I don't think it would really simplify
the initialization code. Mostly it would change its location.

> (And after marinating on this over the weekend, it occurred to me that
> keeping the per-connection option while making the PRNG global
> introduces an additional hazard, because two concurrent connections
> can now fight over the seed value.)

I think since setting the initial seed value is really only meant for testing
it's not a big deal if it doesn't work with concurrent connections.