From: | "ktm(at)rice(dot)edu" <ktm(at)rice(dot)edu> |
---|---|
To: | Magnus Hagander <magnus(at)hagander(dot)net> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: sync_seqscans in postgresql.conf |
Date: | 2011-12-20 13:47:05 |
Message-ID: | 20111220134705.GT28286@staff-mud-56-27.rice.edu |
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Lists: | pgsql-hackers |
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.
Regards,
Ken
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