Problem indexing add Simple Table Inherance

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

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

Matt Jones wrote:

add_index will accept an array of columns:

add_index :general_elements, [:type, :id]

--Matt Jones