Re: index prefetching

Wow, quick response.

OS eviction is only implemented in the python version. But the most
intriguing part is that the python version also shows a degradation by
simply evicting with pg_buffeercache_evict. I checked many times, first I
thought that my differences had a sign inversion. Then I thought it could
be something about the python speed, could it be? I am timing with explain
analyse, if I was fetching the rows this would be the obvious culprit.

How did you account for the OS filesystem cache? It looks like you
> didn't, based on this run_benchmarks.sh code:
>

Sorry I attached the wrong file. I didn't use this run_benchmark.sh.

> How should I go about recreating your result? This was my best guess
> at how to do so. But it doesn't feel like a good guess.

Could you try running the python script or should I provide it in a
different way?

> Are the numbers you showed comparing the patch to the master branch?
> Or is it just comparing enable_indexscan_prefetch=on to
> enable_indexscan_prefetch=off with the patch?

Just changing the parameter.

> Did you write all this test code yourself?
>

In the sense of typing it no, I used cursor, so I just edited what I could
see it didn't get right.

The results you've shown put the patch in a very negative light -- at
> least if taken at face value.

Please notice that I tried to be neutral in the narrative.

Maybe because I tested on a MacOS maybe it works differently from the type
of
"modern storage" mentioned at the start of the thread.

There's no point in speculating what might have happened here until I
> can reproduce your results
>

I totally agree, that is why my first step was to try to reproduce your
results independently.

I see another message, checking that.

--
Alexandre