Re: index prefetching

Hi Tomas,

> I've decided to run a couple tests, trying to reproduce some of the
> behaviors described in your (Felipe's) messages.
> ...
> I'm attaching the full scripts, raw results, and PDFs with a nicer
> version of the results.

> The results are pretty positive. For random data (which is about the
> worst case for I/O), it's consistently faster than master. Yes, the
> gains with 8 workers is not as significant as with 1 worker. For
> example, it may look like this:
>
> master prefetch
> 1 worker: 2960 1898 64%
> 8 workers: 5585 5361 96%

branch: patched
data: random
io: buffered

patched master
iomethod io_uring worker io_uring worker
workers
1 1.52 1.29 2.79 2.75
2 1.77 1.63 3.03 3.04
4 2.36 4.24 3.44 3.40
8 3.60 8.53 4.30 4.30

They are about the same for 1 worker, but degrade as the number of
workers increase, to be honest I was expecting this behaviour IO not
with buffered. But as you pointed out using io_unring the issue goes
away.

Lock contention in pgaio_worker_submit_internal?
Or maybe nsync > 0 at the bottom of the function?
(in src/backend/storage/aio/method_worker.c)

Regards