[rspec-users] NullDb makes rake spec take (much) longer

Ben Mabey ben at benmabey.com
Mon Jan 12 12:36:16 EST 2009

On 1/12/09 7:09 AM, Matt Wynne wrote:
> Hi all,
> We did a spike last week to de-couple our view and controller tests 
> from the database, using NullDb. It didn't go too well. I realise that 
> this plugin isn't part of RSpec, but I thought others on this list 
> might have experiences to share.
> Here's a summary of my colleague's investigations:
>> I installed the plugin from http://github.com/jakehow/nulldb/tree/master
>> Changed spec/spec_helper to set
>> "ActiveRecord::Base.establish_connection(:adapter => :nulldb)" by
>> default.
>> The specs that complained of the lack of db, I included a before(all)
>> that changed the connection to the test database (include
>> NeedsDatabase - copied from Ben Mabey's Functional module)
>> By default, I also included the db for all models (config.include
>> NeedsDatabase, :type => :model)
>> Running spec spec/views with or without nulldb takes about the same
>> time (a couple of seconds less with nulldb). However, running "rake
>> spec" with nulldb takes 10 times longer!!
>> Another weird thing was that three tests failed in the controllers
>> (venues and concerts) in a very strange way, even when I included the
>> NeedsDatabase in the tests that needed it. The weird bit is, when I
>> run: "spec spec/controllers/venues_controller_spec.rb" it doesn't
>> fail. But when I run: "spec spec/controllers/users_controller_spec.rb
>> spec/controllers/venues_controller_spec.rb" It does fail... That is,
>> the user_controller test is influencing the results of the
>> venue_controller test!
>> The same weird behaviour happens in lib/sk/find
>> This made me had to include NeedsDatabase for all lib and controllers
>> tests as well.
> The barrier for us was the shockingly poor performance of 'rake spec' 
> on the view specs - it really means we just can't use it, and actually 
> only barely improved the performance of the specs at all.
> I was disappointed that the view specs didn't get any faster. My guess 
> is that stub_model is the problem - as it has to do quite a bit of 
> work to set up the attributes on the models.
> So, can anyone tell us what we might have been doing wrong? Or did I 
> just have unrealistic expectations of how this might help?
> Matt Wynne
> http://blog.mattwynne.net
> http://www.songkick.com
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Hey Matt,
I had similar experiences when I started using NullDB.  I think that the 
reason why the overall spec suite runs slow is AR is switching from one 
adapter to another, and in the case of the mysql one it probably is 
relatively expensive to set up a new connection.  Switching over to 
using NullDB on an existing project of any sizable size is going to be 
large task IMO.  On my last project we started using NullDB by default 
and the result has been very worthwhile and noticeable.  In this project 
DB connectivity was the exception, not the norm (even on our model 
specs) and so that is why I created a module that would turn on the DB 
temporarily.  In your case the opposite approach may be needed.

Going back to the problem at hand... Based on the email you are using a 
module like this:
   unless Object.const_defined?(:NeedsDatabase)
     share_as :NeedsDatabase do

       before :all do

       after :all do
         ActiveRecord::Base.establish_connection(:adapter => :nulldb)

Since you are including this on all of your model specs (and more) you 
are incurring the setup and teardown cost of the DB connection 
repeatedly.  Like I said, you may want to adopt the opposite policy of 
turning it off temporarily... You could also make the the changing 
smarter by only changing it when you need to.. something like:

share_as :NeedsDatabase do
     before :all do
         ActiveRecord::Base.establish_connection(:test) if 
ActiveRecord::Base.connection.class.to_s =~ /NullDB/
share_as :DontNeedDatabase do
     before :all do
         ActiveRecord::Base.establish_connection(:adapter => :nulldb) 
unless ActiveRecord::Base.connection.class.to_s =~ /NullDB/

With this approach you would need to specify whether or not to use the 
DB for each example group... just a thought.  Of course, an even better 
solution would be to somehow modify AR to maintain an active connection 
to the real DB even when it isn't the active adapter.

re: the view specs
I wouldn't expect to see too much gain here.   The big win for nullDB is 
in models IMO.  Of course, having it on the view and controller specs 
helps prevent accidental DB calls.

re: the random controller spec failures
I only guess is that you are somehow relying on the DB in your 
controller specs.  I did this too in my controllers when I called class 
methods on models that would get a list from the DB... I can't really 
help without seeing any specs though.

I hope this helps and you can find a suitable policy on how to manage 
the connections/adapters.  Just ask if you have any other questions.


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