Thread

Re: Subtransactions + a long-running transaction leading to performance degradation on standbys

Nikolay Samokhvalov <nik@postgres.ai> — 2021-08-20T05:09:45Z

On Thu, Aug 19, 2021 at 10:04 PM Andrey Borodin <x4mmm@yandex-team.ru>
wrote:

> I just want to note, that on your screenshot unpatched version runs 400K
> tps, while patched runs 280K tps. I see the dates are different and this
> effect is not observed in  [0]. Probably, you run tests on different
> machines.


Indeed, patched Postgres I was testing on 2x smaller EC2 instances, it is
documented in the GitLab issue. But I added an additional note here:
https://gitlab.com/postgres-ai/postgresql-consulting/tests-and-benchmarks/-/issues/21#note_655731979


> While your experiments clearly shows that patch can save DB from
> degradation under pathological workload it would be great to ensure patch
> does not incur penalty on normal workload.
>

Makes sense. I'll try to find time to make a direct comparison.

I documented all the steps in detail in the GitLab issue, so anyone
interested can reproduce it and explore the problem at different angles.