Re: [HACKERS] PinBuffer() no longer makes use of strategy

On 2/4/17 2:47 PM, Alexander Korotkov wrote:
> On Sat, Feb 4, 2017 at 4:33 AM, Andres Freund  > 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.

This patch looks pretty straight forward and applies cleanly and
compiles at cccbdde.

It's not a straight revert, though, so still seems to need review.

Jim, do you know when you'll have a chance to look at that?

-- 
-David
david@pgmasters.net