Re: pgbench rate limiting changes transaction latency computation

On 12/06/2019 02:24, Andres Freund wrote:
> But anyway, to go forward, I think we should replace 'lat' with a
> 'txtime' (or similar) column that is not affected by -R. And then, under
> -R only, add a new 'txlat' column, that shows the 'current' meaning of
> lat under -R. Not convinced the names are right, but you get the gist.

I'm OK with that.

>> For testing the server under full load, like during that catch up period,
>> testing without -R seems better.
>
> One area in which postgres is pretty weak, although less bad than we
> used to be, is in is predicatable latency. Most production servers
> aren't run under the highest possible throughput, therefore optimizing
> jitter under loaded but not breakneck speeds is important.
>
> And to be able to localize where such latency is introduced, it's
> important to see the precise moment things got slower / where
> performance recovered.

I agree with all that. I'm still not convinced the changes you're
proposing will help much, but if you would find it useful, I can't argue
with that.

- Heikki