Re: [RFC, POC] Don't require a NBuffer sized PrivateRefCount array of local buffer pins

On Wed, Apr 9, 2014 at 6:02 PM, Andres Freund <andres(at)2ndquadrant(dot)com>wrote:

>
>
> I've tried to reproduce problems around this (when I wrote this), but
> it's really hard to construct cases that need more than 8 pins. I've
> tested performance for those cases by simply not using the array, and
> while the performance suffers a bit, it's not that bad.
>
>
AFAIR this was suggested before and got rejected because constructing that
worst case and proving that the approach does not perform too badly was a
challenge. Having said that, I agree its time to avoid that memory
allocation, especially with large number of backends running with large
shared buffers.

An orthogonal issue I noted is that we never check for overflow in the ref
count itself. While I understand overflowing int32 counter will take a
large number of pins on the same buffer, it can still happen in the worst
case, no ? Or is there a theoretical limit on the number of pins on the
same buffer by a single backend ?

Thanks,
Pavan

--
Pavan Deolasee
http://www.linkedin.com/in/pavandeolasee