gistfile1.md

FriendlyId uses Rails's extending method to avoid overwriting your model's find method. Internally this is implemented similar to this:

def self.friendly
  all.extending(friendly_id_config.finder_methods)
end

This however comes with a performance impact, because extending invokes Ruby's extend, which blows away MRI's method cache. To work around this, FriendlyId lets you include a :finders module which overrides your model's find to increase performance.

As of Ruby 2.1 though, extend only blows away the current classes' method cache. Behold the difference:

Using ruby 2.0.0 AR 4.0.2 with sqlite3 (in-memory)
                                                   user     system      total        real
find (in-table slug)                           0.820000   0.000000   0.820000 (  0.837980)
find (in-table slug; using finders module)     0.390000   0.000000   0.390000 (  0.408671)

------------------------------------------------------------------------

Using ruby 2.1.0 AR 4.0.2 with sqlite3 (in-memory)

                                                   user     system      total        real
find (in-table slug)                           0.480000   0.000000   0.480000 (  0.491496)
find (in-table slug; using finders module)     0.400000   0.010000   0.410000 (  0.398222)

While you still incur some cost for invoking extend, it's much, much cheaper in 2.1 than in previous versions.