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

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От Pavan Deolasee
Тема Re: [RFC, POC] Don't require a NBuffer sized PrivateRefCount array of local buffer pins
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Msg-id CABOikdP2=0MXzy-jTo0s2tzZ_UKRhN7m1J=dtZQY=6T-wMNGng@mail.gmail.com
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Ответ на Re: [RFC, POC] Don't require a NBuffer sized PrivateRefCount array of local buffer pins  (Andres Freund <andres@2ndquadrant.com>)
Ответы Re: [RFC, POC] Don't require a NBuffer sized PrivateRefCount array of local buffer pins  (Andres Freund <andres@2ndquadrant.com>)
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On Wed, Apr 9, 2014 at 6:02 PM, Andres Freund <andres@2ndquadrant.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

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