Re: sync_seqscans in postgresql.conf

On Tue, Dec 20, 2011 at 14:47, ktm(at)rice(dot)edu <ktm(at)rice(dot)edu> wrote:
> On Tue, Dec 20, 2011 at 02:41:54PM +0100, Magnus Hagander wrote:
>> On Tue, Dec 20, 2011 at 14:38, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> > On Tue, Dec 20, 2011 at 8:35 AM, Magnus Hagander <magnus(at)hagander(dot)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.

Yes, but they may also come out in a different order if you run the
same query again 5 minutes later...

--
 Magnus Hagander
 Me: http://www.hagander.net/
 Work: http://www.redpill-linpro.com/