Re: Remove fsync ON/OFF as a visible option?

On Wed, Mar 25, 2015 at 12:45 PM, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>
wrote:

>
> I see 3 settings that allow people to accidentally shoot themselves in the
> foot; fsync, wal_sync_method and full_page_writes.
>
> How about just grouping those 3 together with a bulk disclaimer along the
> lines of "The following 3 settings are dangerous. Use at your own risk, and
> read the docs first."? That would also allow us to just remove the comments
> about what the settings do; if you don't already know you certainly
> shouldn't be touching them! :)
>
>
But one of these things is not like the other. Any supported (i.e. non
fatal erroring) setting of wal_sync_method *should* always be safe
(although may be inefficient) if the underlying kernel, RAID controller,
hard drives, and fs fulfill their pledges. It is hard to document every
known liar in this regard. About the best you can do, short of
pull-the-plug test on a massive scale, is to run pg_fsync_test and assuming
that any result inconsistent with the RPM of the spinning rust is obviously
unsafe. Unfortunately that doesn't rule out the possibility that something
is both unsafe and gratuitously slow.

Cheers,

Jeff