Re: [HACKERS] [POC] Faster processing at Gather node

Hi,

On 2018-02-27 16:03:17 -0500, Robert Haas wrote:
> On Wed, Feb 7, 2018 at 1:41 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> > Well, it's more than just systems like that - for 64bit atomics we
> > sometimes do fall back to spinlock based atomics on 32bit systems, even
> > if they support 32 bit atomics.
>
> I built with -m32 on my laptop and tried "select aid, count(*) from
> pgbench_accounts group by 1 having count(*) > 1" on pgbench at scale
> factor 100 with pgbench_accounts_pkey dropped and
> max_parallel_workers_per_gather set to 10 on (a) commit
> 0b5e33f667a2042d7022da8bef31a8be5937aad1 (I know this is a little old,
> but I think it doesn't matter), (b) same plus
> shm-mq-less-spinlocks-v3, and (c) same plus shm-mq-less-spinlocks-v3
> and shm-mq-reduce-receiver-latch-set-v2.
>
> (a) 16563.790 ms, 16625.257 ms, 16496.062 ms
> (b) 17217.051 ms, 17157.745 ms, 17225.755 ms [median to median +3.9% vs. (a)]
> (c) 15491.947 ms, 15455.840 ms, 15452.649 ms [median to median -7.0%
> vs. (a), -10.2% vs (b)]
>
> Do you think that's a problem? If it is, what do you think we should
> do about it? It seems to me that it's probably OK because (1) with
> both patches we still come out ahead and (2) 32-bit systems will
> presumably continue to become rarer as time goes on, but you might
> disagree.

No, I think this is fairly reasonable. A fairly extreme usecase on a 32
bit machine regressing a bit, while gaining peformance in other case?
That works for me.

> OK, I'll try to check how feasible that would be.

cool.

Greetings,

Andres Freund