Problem indexing add Simple Table Inherance

[John Smith]

I have a simple table inherance, with an upper class GeneralElement. A
class that inherits is Activity:
class Activity < GeneralElement
...
end

The GeneralElement table is very big (about 2.000.000 rows!). Other
classes that inherit from GeneralElement return queries very fast, but
Activity.last is very slow. I have added indexes to id and type, but it
has no effect. What can I do?

I'll appreciate any help
--
Posted via http://www.ruby-forum.com/.

[Matt Jones]

On Mar 11, 4:50 am, John Smith <li...@ruby-forum.com> wrote:
> I have a simple table inherance, with an upper class GeneralElement. A
> class that inherits is Activity:
> class Activity < GeneralElement
> ...
> end
>
> The GeneralElement table is very big (about 2.000.000 rows!). Other
> classes that inherit from GeneralElement return queries very fast, but
> Activity.last is very slow. I have added indexes to id and type, but it
> has no effect. What can I do?

You may want to grab the query that Activity.last is using, and try
running it through 'EXPLAIN' to see what it's looking for. Have you
defined an order (via default_scope, for instance) on Activity? You
might need to have an index on that field together with 'type' to get
right behavior.

--Matt Jones

[John Smith]

I have added an index to the type column; but maybe it's possible to add
a special index to both the id and type column at the same time. How
could I do this?

[Matt Jones]

add_index will accept an array of columns:

add_index :general_elements, [:type, :id]

--Matt Jones