On Thu, Jul 15, 2010 at 12:04:21PM +0200, Hans-Jürgen Schönig wrote:
> hello ...
>
> a view is already nice but i think it is still too narrow.
One sure way to fail is to take on a problem in chunks too large. If
we get even one of the cross-column issues solved by statistics, we'll
be ahead of
On Thu, Jul 15, 2010 at 12:04:21PM +0200, Hans-Jürgen Schönig wrote:
> hello ...
>
> a view is already nice but i think it is still too narrow.
> the problem is: you don't want a view for every potential join.
> in addition to that - ideally there is not much left of a view when it comes
> to ch
hello ...
a view is already nice but i think it is still too narrow.
the problem is: you don't want a view for every potential join.
in addition to that - ideally there is not much left of a view when it comes to
checking for costs.
so, i think, this is not the kind of approach leading to total
Joshua Tolley writes:
>> >> ALTER TABLE x SET CORRELATION STATISTICS FOR (x.id =3D y.id AND x.id=
2 =3D y.id2)
>> >=20
>> it says X and Y ... the selectivity of joins are what i am most
>> interested in. cross correlation of columns within the same table are
>> just a byproduct. the core thing
On Wed, Jul 14, 2010 at 5:13 PM, Robert Haas wrote:
> 2010/7/14 Tom Lane :
>> If the combination of columns is actually interesting, there might well
>> be an index in place, or the DBA might be willing to create it.
>
> Indexes aren't free, though, nor even close to it.
>
> Still, I think we shou
2010/7/14 Tom Lane :
> If the combination of columns is actually interesting, there might well
> be an index in place, or the DBA might be willing to create it.
Indexes aren't free, though, nor even close to it.
Still, I think we should figure out the underlying mechanism first and
then design th
On Wed, Jul 14, 2010 at 04:41:01PM +0200, PostgreSQL - Hans-Jürgen Schönig
wrote:
> hello ...
>
> look at the syntax i posted in more detail:
>
> >>ALTER TABLE x SET CORRELATION STATISTICS FOR (x.id = y.id AND x.id2 =
> >> y.id2)
> >
> it says X and Y ...
> the selectivity of joins are wha
hello ...
look at the syntax i posted in more detail:
>> ALTER TABLE x SET CORRELATION STATISTICS FOR (x.id = y.id AND x.id2 =
>> y.id2)
>
it says X and Y ...
the selectivity of joins are what i am most interested in. cross correlation of
columns within the same table are just a byprod
Tom Lane wrote:
If the combination of columns is actually interesting, there might well
be an index in place, or the DBA might be willing to create it.
I'm having a hard time imagining an interesting case where that wouldn't
be so.
For
that matter, have you considered the idea of examin
=?iso-8859-1?Q?PostgreSQL_-_Hans-J=FCrgen_Sch=F6nig?=
writes:
> i think that having stats on an index is a problem by itself for 2 reasons -
> for cross column correlation at least:
> a.) joins cannot be covered by an index on two tables - we would fix
> "inside a table correlation probl
hello tom,
i think that having stats on an index is a problem by itself for 2 reasons -
for cross column correlation at least:
a.) joins cannot be covered by an index on two tables - we would fix
"inside a table correlation problems" but not joins.
b.) who says that there is act
On Wed, Jul 14, 2010 at 01:21:19PM +0200, Yeb Havinga wrote:
> Heikki Linnakangas wrote:
>> However, the problem is how to represent and store the
>> cross-correlation. For fields with low cardinality, like "gender" and
>> boolean "breast-cancer-or-not" you can count the prevalence of all the
Heikki Linnakangas writes:
> On 14/07/10 13:12, PostgreSQL - Hans-Jürgen Schönig wrote:
>> maybe somehow like this ...
>> ALTER TABLE x SET CORRELATION STATISTICS FOR (id = id2 AND id3=id4)
> +1 is my general feeling, it's good if you can tell the system to
> collect additional statistics where
Heikki Linnakangas wrote:
However, the problem is how to represent and store the
cross-correlation. For fields with low cardinality, like "gender" and
boolean "breast-cancer-or-not" you can count the prevalence of all the
different combinations, but that doesn't scale. Another often cited
exam
On Jul 14, 2010, at 12:40 PM, Heikki Linnakangas wrote:
> On 14/07/10 13:12, PostgreSQL - Hans-Jürgen Schönig wrote:
>> hello everybody,
>>
>> we are currently facing some serious issues with cross correlation issue.
>> consider: 10% of all people have breast cancer. we have 2 genders (50:50).
>
On 14/07/10 13:12, PostgreSQL - Hans-Jürgen Schönig wrote:
hello everybody,
we are currently facing some serious issues with cross correlation issue.
consider: 10% of all people have breast cancer. we have 2 genders (50:50).
if i select all the men with breast cancer, i will get basically nobody
hello everybody,
we are currently facing some serious issues with cross correlation issue.
consider: 10% of all people have breast cancer. we have 2 genders (50:50).
if i select all the men with breast cancer, i will get basically nobody - the
planner will overestimate the output.
this is the com
17 matches
Mail list logo
