The default dashboard "last used" field is very expensive and should be removed

[vincentwoo]

In dashboard.rb, RailsAdmin does the following for every table by default:

@most_recent_changes[t.model.name] =
  t.first(sort: "#{t.table_name}.updated_at").try(:updated_at)

This is an ENORMOUSLY expensive call for any table that is not indexed on updated_at. For example, on my app:

coderpad-rails=# EXPLAIN SELECT  "pads".* FROM "pads"  ORDER BY pads.updated_at desc LIMIT 1;
                                 QUERY PLAN
----------------------------------------------------------------------------
 Limit  (cost=25411.89..25411.89 rows=1 width=1203)
   ->  Sort  (cost=25411.89..25811.53 rows=159859 width=1203)
         Sort Key: updated_at
         ->  Seq Scan on pads  (cost=0.00..24612.59 rows=159859 width=1203)
(4 rows)

This is occasionally causing complete HTTP timeouts in my application. I don't want to add an index just to service this dashboard, either. I'm going to turn off statistics entirely because there doesn't seem to be a way to disable just this behavior, but I'd recommend either adding a flag or just showing something much easier, like the created_at time on the last row in the table.

[nynhex]

@vincentwoo I'm having the exact same problem in both old versions of rails_admin and new versions. It's super expensive to load the stats page and often my app will timeout for 2-4min at a same.

Is there any way to disable the stats to avoid these expensive calls?

[codealchemy]

@shakycode The stats bar can be disabled (more on that here):

RailsAdmin.config do |c|
  c.actions do
    dashboard do
      statistics false
    end
  end
end

You could also build your own custom dashboard in app/views/rails_admin/main/dashboard.html.erb (or .haml, depending on your project)

[vincentwoo]

I did that as well, but I think it is not a good default for rails_admin to have.

[bbenezech]

What should we do instead?
Is the sorting important?
If not, maybe you can provide a pull request sorting by id?

[vincentwoo]

I can. Are you open to that idea?

[bbenezech]

Sure!
We'll call it "last entries" instead of "last updates" I guess. 👯