Re: [HACKERS] Re: pgsql: Avoid extra locks in GetSnapshotData if old_snapshot_threshold <

On Tue, Apr 12, 2016 at 2:53 PM, Kevin Grittner <kgrittn(at)gmail(dot)com> wrote:
> Readonly with client and job counts matching scale.

Single-socket i7, BTW.

>> A lot of this will be different between
>> single-socket and multi-socket servers; as soon as you have the latter
>> the likelihood of contention being bad goes up dramatically.
>
> Yeah, I know, and 4 socket has been at least an order of magnitude
> more problematic in my experience than 2 socket. And the problems
> are far, far, far worse on kernels prior to 3.8, especially on 3.x
> before 3.8, so it's hard to know how to take any report of problems
> on a 4 node NUMA machine without knowing the kernel version.

Also, with 4 node NUMA I have seen far better scaling with
hyper-threading turned off. I know there are environments where it
helps, but high-concurrency on multi-node NUMA is not one of them.

So, anyway, mentioning the HT setting is important, too.

Kevin Grittner