Re: Partitioning

Hello,

Thanks for the reply. I can write queries which get index scans, but they
are still slow.

Each index is about 2.5GB, I suspect I am trying to read a these into
memory in entirety.

Perhaps there is no way to tune this?

Cheers, james

On Monday, 19 January 2015, Kyotaro HORIGUCHI <
horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> wrote:

> Hello,
>
> an 2015 14:13:37 +1100, James Sewell <james(dot)sewell(at)lisasoft(dot)com
> <javascript:;>> wrote in <
> CANkGpBs8GypQ3TQGKdjTD+n-w1rkq5uO97h3tuhg5eWaKR6RbA(at)mail(dot)gmail(dot)com
> <javascript:;>>
> > Sadly not ... I still hit all the tables.
>
> | 5.9.4. Partitioning and Constraint Exclusion
>
> http://www.postgresql.org/docs/9.4/static/ddl-partitioning.html
>
> Constraint exclusion is a mechanism to omit tables that are known
> to have no hit by the query *beforehand* execution. So the
> criteria cannot rely on out of the query itself (and CHECK
> constraints, of course).
>
> Your query uses the result of the WITH-clause-query in the WHERE
> clause which is unknown to the planner so constraint exclusion
> does not work. JOINs don't change the situation.
>
>
> > On Mon, Jan 19, 2015 at 1:54 PM, John R Pierce <pierce(at)hogranch(dot)com
> <javascript:;>> wrote:
> >
> > > On 1/18/2015 5:58 PM, James Sewell wrote:
> > >
> > > WITH idlist as (SELECT id from othertable)
> > > SELECT id from mastertable WHERE id = idlist.id);
> > >
> > >
> > >
> > > select mt.id, ... from mastertable mt join othertable ot on
> mt.id=
> > > ot.id;
> > >
> > > might optimize better.
>
> As the result, the query inevitably scans all the tables, but not
> necessariry in sequqntial scans or simple index scans. The
> suggestion above seeems showing the notation which the planner
> can find the better plans on that premise.
>
> For example, if you have an index on id of one of the two tables,
> (and some other conditions match, of course) index only scan will
> be selected for it and the suggested query will give you a
> seemingly better plan than your query.
>
> regards,
>
> --
> Kyotaro Horiguchi
> NTT Open Source Software Center
>
>

--

James Sewell,
PostgreSQL Team Lead / Solutions Architect
______________________________________

Level 2, 50 Queen St, Melbourne VIC 3000

*P *(+61) 3 8370 8000 *W* www.lisasoft.com *F *(+61) 3 8370 8099

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