Re: Move PinBuffer and UnpinBuffer to atomics

On 2016-02-01 13:06:57 +0300, Alexander Korotkov wrote:
> On Mon, Feb 1, 2016 at 11:34 AM, Alexander Korotkov <
> a.korotkov@postgrespro.ru> wrote:
> >> Client    Base    Patch
> >> 1    19744    19382
> >> 8    125923    126395
> >> 32    313931    333351
> >> 64    387339    496830
> >> 128    306412    350610
> >>
> >> Shared Buffer= 512MB
> >> max_connections=150
> >> Scale Factor=300
> >>
> >> ./pgbench  -j$ -c$ -T300 -M prepared -S postgres
> >>
> >> Client    Base    Patch
> >> 1    17169    16454
> >> 8    108547    105559
> >> 32    241619    262818
> >> 64    206868    233606
> >> 128    137084    217013

So, there's a small regression on low client counts. That's worth
addressing.

> Attached patch is rebased and have better comments.
> Also, there is one comment which survive since original version by Andres.
> 
> /* Add exponential backoff? Should seldomly be contended tho. */
> 
> 
> Andres, did you mean we should twice the delay with each unsuccessful try
> to lock?

Spinning on a lock as fast as possible leads to rapid cacheline bouncing
without anybody making progress. See s_lock() in s_lock.c.

Greetings,

Andres Freund