Re: sync_seqscans in postgresql.conf

On Tue, Dec 20, 2011 at 02:41:54PM +0100, Magnus Hagander wrote:
> On Tue, Dec 20, 2011 at 14:38, Robert Haas <robertmhaas@gmail.com> wrote:
> > On Tue, Dec 20, 2011 at 8:35 AM, Magnus Hagander <magnus@hagander.net> wrote:
> >> Is there any reason why the setting synchronize_seqscans is in the
> >> section "version/platform compatibility" in postgresql.conf? Is it
> >> just because nobody could find a better place for it? ;) It seems a
> >> bit wrong to me...
> >
> > Presumably the thought was that you would turn it off to restore that
> > existed in older versions of PostgreSQL.  Doesn't seem much different
> > from default_with_oids or lo_compat_privileges.
>
> Seems very different to me - those change *what* happens when you do
> certain things. sync_seqscans is just a performance tuning option, no?
> It doesn't actually change the semantics of any operations...
>

In a query without enforced orders, the returned rows will come out in
a possibly different order each time the query runs. I know it is bad
coding to depend on things like that, but it is out there... So in those
cases it is not just semantics.

Regards,
Ken