<p>In db/migrate/20140519141742_add_join_table_between_users_and_changesets.rb:</p>
<pre style='color:#555'>> @@ -0,0 +1,11 @@
> +require 'migrate'
> +class AddJoinTableBetweenUsersAndChangesets < ActiveRecord::Migration
> +  def change
> +    create_table :changesets_subscribers, id: false do |t|
> +      t.column :subscriber_id, :bigint, null: false
> +      t.column :changeset_id, :bigint, null: false
> +    end
</pre>
<p>My understanding is you want the more selective first in composite indexes, which probably means a unique index on <code>[:changeset_id, :subscriber_id]</code> and <code>[:subscriber_id]</code> for the other.</p>

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