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Editorial Team
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Asked: 2026-06-12T21:19:33+00:00

I’m working on an existing Rails 2 site with a large codebase that recently

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I’m working on an existing Rails 2 site with a large codebase that recently updated to Ruby 1.9.2 and the mysql2 gem. I’ve noticed that this setup allows for non-blocking database queries; you can do client.query(sql, :async => true) and then later call client.async_result, which blocks until the query completes.

It seems to me that we could get a performance boost by having all ActiveRecord queries that return a collection decline to block until a method is called on the collection. e.g.

@widgets = Widget.find(:all, :conditions=> conditions) #sends the query
do_some_stuff_that_doesn't_require_widgets
@widgets.each do #if the query hasn't completed yet, wait until it does, then populate @widgets with the result. Iterate through @widgets
...

This could be done by monkey-patching Base::find and its related methods to create a new database client, send the query asynchronously, and then immediately return a Delegator or other proxy object that will, when any method is called on it, call client.async_result, instantiate the result using ActiveRecord, and delegate the method to that. ActiveRecord association proxy objects already work similarly to implement ORM.

I can’t find anybody who’s done this, though, and it doesn’t seem to be an option in any version of Rails. I’ve tried implementing it myself and it works in console (as long as I append ; 1 to the line calling everything so that to_s doesn’t get called on the result). But it seems to be colliding with all sorts of other magic and creating various problems.

So, is this a bad idea for some reason I haven’t thought of? If not, why isn’t it the way ActiveRecord already works? Is there a clean way to make it happen?

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1 Answer

  1. Editorial Team

    I suspect that that .async_result method isn’t available for all database drivers; if not, it’s not something that could be merged into generic ActiveRecord calls.

    A more portable way to help performance when looping over a large recordset would be to use find_each or find_in_batches. I think they’ll work in rails 2.3 as well as rails 3.x. http://guides.rubyonrails.org/active_record_querying.html#retrieving-multiple-objects-in-batches

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