Development Blog: Viget Labs

Have you ever looked in your development log and seen something like the following?

Processing FoosController#show (for ...) [GET]
  Session ID: BAh7CDoOcmV0dXJuX3R...
  SQL (0.000869) SHOW TABLES
  SQL (0.000931) SHOW TABLES
  Image Load (0.000465) SELECT images.* FROM ...
  [...]
Rendered entries/_detail (0.00221)
Rendered entries/_detail (0.00103)
Rendered entries/_detail (0.00118)
Rendered entries/_detail (0.00092)
Rendered entries/_detail (0.00107)
Rendered entries/_detail (0.00069)
Rendered entries/_detail (0.00215)
Rendered entries/_detail (0.00113)
Rendered entries/_detail (0.00113)
Rendered entries/_detail (0.00098)
Rendered entries/_detail (0.00098)
Rendered entries/_detail (0.00087)
Rendered entries/_detail (0.00079)
Rendered entries/_detail (0.00086)
Rendered entries/_detail (0.00079)
Rendered entries/_detail (0.00087)
Rendered entries/_detail (0.00076)
Rendered entries/_detail (0.00081)
Rendered shared/_nav (0.00207)
Rendered shared/_analytics (0.00011)
Rendered shared/_footer (0.00188)
Completed in 1.63867 (0 reqs/sec) | Rendering: 0.40653 (24%) ...

These sorts of entries in the log have always felt like a code smell to me - even when some sort of markup reuse is obviously necessary (so you can't just do it inline), I can't help but think that there's some significant cost to rendering the same file over and over again. So after a long time of thinking about it, I finally got around to doing some benchmarks comparing generating markup in a helper method, rendering a partial repeatedly for a collection, and rendering a partial with the :collection key. For each method, I use apache benchmark to hit a page 1000 times (with 2 simultaneous requests); each request generated 1000 divs like this:

<div>
  <span>index</span>
  <a href="#">link</a>
</div>

Here's what I found:

So it looks like there is a cost to rendering a partial repeatedly, but that cost can be reduced by using the :collection key, and reduced even further by generating the markup in a helper method. Of course, the helper method can be a smell of its own, but if performance is an issue it may be worth a look.

Note: This is an unscientific test, so feel free to respond with your own benchmarks.