Re: PinBuffer() no longer makes use of strategy

On Sat, Feb 4, 2017 at 4:33 AM, Andres Freund <andres(at)anarazel(dot)de> wrote:

> On 2017-02-03 19:13:45 -0600, Jim Nasby wrote:
> > No, I noticed it while reading code. Removing that does mean that if any
> > non-default strategy (in any backend) hits that buffer again then the
> buffer
> > will almost certainly migrate into the main buffer pool the next time
> one of
> > the rings hits that buffer
>
> Well, as long as the buffer is used from the ring, BufferAlloc() -
> BufferAlloc() will reset the usagecount when rechristening the
> buffer. So unless anything happens inbetween the buffer being remapped
> last and remapped next, it'll be reused. Right?
>
> The only case where I can see the old logic mattering positively is for
> synchronized seqscans. For pretty much else that logic seems worse,
> because it essentially prevents any buffers ever staying in s_b when
> only ringbuffer accesses are performed.
>
> I'm tempted to put the old logic back, but more because this likely was
> unintentional, not because I think it's clearly better.
>

+1
Yes, it was unintentional change. So we should put old logic back unless
we have proof that this change make it better.
Patch is attached. I tried to make some comments, but probably they are
not enough.

------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company