I’m experiencing slow performance issues on my app using the kaminari paginate command, and wondering if there might be a way to avoid it.

Here’s the relevant trace:

/kaminari-0.15.1/lib/kaminari/models/active_record_relation_methods.rb:24:in `total_count'
/kaminari-0.15.1/lib/kaminari/models/page_scope_methods.rb:22:in `total_pages'
/kaminari-0.15.1/lib/kaminari/helpers/action_view_extension.rb:18:in `paginate'

And here’s the SQL query, which in my case is related to a Spree backend view:

(209.9ms)  SELECT DISTINCT COUNT(DISTINCT `spree_orders`.`id`) FROM `spree_orders` WHERE (`spree_orders`.`completed_at` IS NOT NULL)

It seems that kaminari needs to know the full count from this table (which in my case is circa 250,000) in order to generate the “LAST” link.

What I’m thinking is, perhaps there’s a way to pass ?page=last into kaminari and have the last page’s number computed only then. If that were the case, we would only need to know whether the count exceeded the number of items per page * the number of pages. Presumably that would be a much faster SQL query than getting the total number each time we run the query.

I’d be interested to know what the community thinks. This would be a huge performance boost for my application, and likely for anyone else working with large data sets.