On Mon, Apr 23, 2018 at 3:14 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> In other words, transparent connection pooling is going to require
> some new mechanism, which third-party code will have to know about,
> for tracking every last bit of session state that might need to be
> preserved or cleared. That's going to be a big project. Maybe some
> of that can piggyback on existing infrastructure like
> InvalidateSystemCaches(), but there's probably still a ton of ad-hoc
> state to deal with. And no out-of-core pooler has a chance of
> handling all that stuff correctly; an in-core pooler will be able to
> do so only with a lot of work.
Why does it have to be completely transparent? As long as the feature
is optional (say, a .conf setting) the tradeoffs can be managed. It's
a reasonable to expect to exchange some functionality for pooling;
pgbouncer provides a 'release' query (say, DISCARD ALL) to be called
upon release back to the pool. Having session state objects (not all
of which we are talking about; advisory locks and notifications
deserve consideration) 'just work' would be wonderful but ought not to
hold up other usages of the feature.
merlin