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

On Sat, Mar 21, 2015 at 11:54:00AM -0400, Tom Lane wrote:
> Stephen Frost <sfrost@snowman.net> writes:
> > At the moment, one could look at our default postgresql.conf and the
> > "turns forced synchronization on or off" and think it's something akin
> > or somehow related to synchronous_commit (which is completely different,
> > but the options are right next to each other..).
> 
> > How about a big warning around fsync and make it more indepenent from
> > the options around it?
> 
> Yeah, the main SGML docs are reasonably clear about the risks of fsync,
> but postgresql.conf doesn't give you any hint that it's dangerous.  Now
> I'm not entirely sure that people who frob postgresql.conf without having
> read the docs can be saved from themselves, but we could do something
> like this:
> 
>  # - Settings -
>  
>  #wal_level = minimal            # minimal, archive, hot_standby, or logical
>                      # (change requires restart)
>  #fsync = on                # turns forced synchronization on or off
> +                                       # (fsync=off is dangerous, read the
> +                                       # (manual before using it)

I think this will help people who find themselves in that file with
few (or wrong) ideas of what this does.

>  #synchronous_commit = on        # synchronization level;
>                      # off, local, remote_write, or on
>  #wal_sync_method = fsync        # the default is the first option
>                      # supported by the operating system:
> 
> Also, I think the short description "turns forced synchronization on or
> off" could stand improvement; it really conveys zero information.  Maybe
> something like "force data to disk when committing"?
> 
> Also, whatever we do here should be reflected into the description strings
> in guc.c.

I don't suppose there's a way to have a single point of truth...

Cheers,
David.
-- 
David Fetter <david@fetter.org> http://fetter.org/
Phone: +1 415 235 3778  AIM: dfetter666  Yahoo!: dfetter
Skype: davidfetter      XMPP: david.fetter@gmail.com

Remember to vote!
Consider donating to Postgres: http://www.postgresql.org/about/donate