Re: Pooling in Core WAS: Need help in performance tuning.

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Thu, Jul 22, 2010 at 5:29 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>>> The problem is harder for us because a backend can't switch identities
>>> once it's been assigned to a database. I haven't heard an adequate
>>> explanation of why that couldn't be changed, though.

>> Possibly it might decrease the performance significantly enough by
>> reducing the cache locality (syscache, prepared plans)?

> Those things are backend-local. The worst case scenario is you've got
> to flush them all when you reinitialize, in which case you still save
> the overhead of creating a new process.

"Flushing them all" is not zero-cost; it's not too hard to believe that
it could actually be slower than forking a clean new backend.

What's much worse, it's not zero-bug. We've got little bitty caches
all over the backend, including (no doubt) some caching behavior in
third-party code that wouldn't get the word about whatever API you
invented to deal with this.

regards, tom lane