Re: Postgres, fsync, and OSs (specifically linux)

Hi,

On 2018-05-22 17:37:28 +0200, Dmitry Dolgov wrote:
> Thanks for the patch. Out of curiosity I tried to play with it a bit.

Thanks.

> `pgbench -i -s 100` actually hang on my machine, because the
> copy process ended up with waiting after `pg_uds_send_with_fd`
> had

Hm, that had worked at some point...

> errno == EWOULDBLOCK || errno == EAGAIN
>
> as well as the checkpointer process.

What do you mean with that latest sentence?

> Looks like with the default
> configuration and `max_wal_size=1GB` it writes more than reads to a
> socket, and a buffer eventually becomes full.

That's intended to then wake up the checkpointer immediately, so it can
absorb the requests. So something isn't right yet.

> I've increased SO_RCVBUF/SO_SNDBUF and `max_wal_size` independently to
> check it, and in both cases the problem disappeared (but I assume only
> for this particular scale). Is it something that was already
> considered?

It's considered. Tuning up those might help with performance, but
shouldn't required from a correctness POV. Hm.

Greetings,

Andres Freund