---
title: Are rails partials actually slow?

date: 2018-03-04T21:38:04Z
status: published
layout: ../layouts/Post.astro
---

At my previous job, we were told not to use partials to clean up our view code, because each rendering of a partial would add around 10ms to the overall response time. After I was told this I did a quick test in my dev environment, but I'd never actually tested the claim on production ... until today!

<!--more-->

## The setup

I created a new rails project and generated a scaffold I called `things`. On the index page, underneath the auto-generated table, I put the following:

```erb
<% if params[:manypartials].present? %>
  <p>Many partials:</p>
  <% 1000.times do %>
    <%= render "simplepartial", iterations: 1 %>
  <% end %>
<% else %>
  <p>One big partial:</p>
  <%= render "simplepartial", iterations: 1000 %>
<% end %>
```

I then created the partial `simplepartial` and added this code:

```erb
<% iterations.times do %>
  <p>This is a simple partial. Hello from the partial!</p>
<% end %>
```

## Results

I launched the dev server with `rails s` and the production server with `rails s -e production`. I ran

`time curl "http://0.0.0.0:3000/things?manypartials=true" > /dev/null`

and

`time curl "http://0.0.0.0:3000/things" > /dev/null`

to make the requests. (The pipe to `/dev/null` is to reduce the time spent printing stuff to the terminal.)

|            | Many partials | One big partial |
| ---------- | ------------: | --------------: |
| Dev        |       44.365s |          0.852s |
| Production |        0.273s |          0.152s |

So it seems that rendering 1000 partials will cause around 100–200ms of extra rendering time. That's certainly not great, but it may not be too high a price to pay for HTML templates not growing to thousands of lines.