Re: pgbench: option delaying queries till connections establishment?

Hi,

On 2020-11-14 20:07:38 +0300, Alexander Korotkov wrote:
> Hmm... Let's see the big picture. You've recently committed a
> patchset, which greatly improved the performance of GetSnapshotData().
> And you're making further improvements in this direction. But you're
> getting trouble in measuring the effect, because Postgres is still
> stuck on ProcArrayLock.

No, the problem was that I couldn't measure the before/after behaviour
reliably, because not all connections actually ever get established
*before* the GetSnapshotData() scability patchset. Which made the
numbers pointless, because we'd often end up with e.g. 80 connections
doing work pre-patch, and 800 post-patch; which obviously measures very
different things.

I think the issue really is that, independent of PG lock contention,
it'll take a while to establish all connections, and that starting to
benchmark with only some connections established will create pretty
pointless numbers.

> And in this thread you propose a workaround
> for that implemented on the pgbench side. My very dumb idea is
> following: should we finally give a chance to more fair lwlocks rather
> than inventing workarounds?

Perhaps - I just don't think it's related to this thread. And how you're
going to address the overhead.

Greetings,

Andres Freund