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

On 3/25/15 8:35 PM, Jeff Janes wrote:
> On Wed, Mar 25, 2015 at 12:45 PM, Jim Nasby <Jim.Nasby@bluetreble.com
> <mailto:Jim.Nasby@bluetreble.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.

I agree, but the reason I include this setting as dangerous is you 
really don't know what you're getting into once you move past fsync 
unless you actually study it and/or do testing. To me, that makes that 
setting dangerous.
-- 
Jim Nasby, Data Architect, Blue Treble Consulting
Data in Trouble? Get it in Treble! http://BlueTreble.com