Re: partitioning query planner almost always scans all tables

>
>
> > EXPLAIN ANALYZE SELECT * FROM measurement_events WHERE
> > measurement_source_id='df86917e-8df0-11e1-8f8f-525400e76ceb' ORDER BY
> > measurement_time DESC LIMIT 1;
> >
> > This seems to fail, scanning all tables. Do you think this can be
> improved
> > at all ? The query plan of the above query is as follows:
>
> The combination of sorting by measurement_source_id and limit
> hinders constraint exclusion because the order of the column
> across whole the inheritance is not known to planner. And the
> below plan also dosn't show whether constraint exclusion worked
> or not, by the same reason. But I suppose it worked.
>

It is ORDER BY measurement_time, not measurement_id, and measurement_time
is used to create the partition. So the planner should know the correct
order, but instead it seems to query tables in the wrong order.