From: | Geoff Winkless <pgsqladmin(at)geoff(dot)dj> |
---|---|
To: | Victor Yegorov <vyegorov(at)gmail(dot)com> |
Cc: | Postgres General <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: index problems (again) |
Date: | 2016-03-07 14:47:13 |
Message-ID: | CAEzk6fd6=nEzabNOL+ANH=pp+=9TERZ_yUi7ijb8N_4-esTrOA@mail.gmail.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-general |
On 7 March 2016 at 14:27, I wrote:
> So it seems that it should in fact be usable after all. So I'm still
> stumped as to why the (scdate,sc_id) index isn't used :(
Also, while the index on sc_id will be sorted there's no guarantee
that sc_id values will be in order in the table itself, so you're
still left with (30,000) potentially random accesses to the table,
even assuming fully random distribution of scdate (with a worst-case
of 970000 random accesses). That average case is no better than the
(30,000) random accesses that were required from using an scdate
index, even ignoring the scdate/sc_id index.
So I'm afraid I'm fully back in the "I still don't get it" column.
Geoff
From | Date | Subject | |
---|---|---|---|
Next Message | Tom Lane | 2016-03-07 14:51:45 | Re: index problems (again) |
Previous Message | Geoff Winkless | 2016-03-07 14:27:17 | Re: index problems (again) |