Re: patch to allow disable of WAL recycling

Alvaro,

I have previously posted ZFS numbers for SmartOS and FreeBSD to this
thread, although not with the exact same benchmark runs that Tomas did.

I think the main purpose of running the benchmarks is to demonstrate that
there is no significant performance regression with wal recycling disabled
on a COW filesystem such as ZFS (which might just be intuitive for a COW
filesystem). I've tried to be sure it is clear in the doc change with this
patch that this tunable is only applicable to COW filesystems. I do not
think the benchmarks will be able to recreate the problematic performance
state that was originally described in Dave's email thread here:

https://www.postgresql.org/message-id/flat/CACukRjO7DJvub8e2AijOayj8BfKK3XXBTwu3KKARiTr67M3E3w%40mail(dot)gmail(dot)com#CACukRjO7DJvub8e2AijOayj8BfKK3XXBTwu3KKARiTr67M3E3w(at)mail(dot)gmail(dot)com

Thanks,
Jerry

On Wed, Aug 22, 2018 at 8:41 AM, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
wrote:

> On 2018-Aug-22, Andres Freund wrote:
>
> > On 2018-08-22 11:06:17 -0300, Alvaro Herrera wrote:
>
> > > I suppose that the use case that was initially proposed (ZFS) has not
> > > yet been tested so we shouldn't reject this patch immediately, but
> > > perhaps what Joyent people should be doing now is running Tomas' test
> > > script on ZFS and see what the results look like.
> >
> > IDK, I would see it less negatively. Yes, we should put a BIG FAT
> > warning to never use this on non COW filesystems. And IMO ZFS (and also
> > btrfs) sucks badly here, even though they really shouldn't. But given
> > the positive impact for zfs & btrfs, and the low code complexity, I
> > think it's not insane to provide this tunable.
>
> Yeah, but let's see some ZFS numbers first :-)
>
> --
> Álvaro Herrera https://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
>