In part 3 of my Ruby on Rails Performance Series we’ll look at how to improve the parsing speed of XML content.
Rails will automatically parse XML in two key places:
1. When XML content is sent to a controller/action pair via POST or PUT. (Your app is an API server.)
2. When XML content is received from an ActiveResource request. (Your app is an API client.)
The default XML parser is REXML. It’s written in pure Ruby which makes it very portable. And slow. Very slow.
So, we need to replace REXML with something faster. The key is the 1libxml-ruby gem which is just a binding to the very fast libxml2 C library.
libxml-ruby has a different set of methods from REXML and is not drop in compatible. If you’re planning on moving your own REXML parsing code to libxml-ruby, it will take some work. However, it’s worth it. In one particular project, I had about a 100x speed improvement!
Rails, as it often does, makes the switch to libxml-ruby super easy. First, install the gem (requires a functioning compiler, the libxml2 library, and headers for libxml2):
1gem install libxml-ruby
Then, just add a new file to 1config/initializers/. Let’s call it 1config/initializers/xml_config.rb. In that file, put this:
1ActiveSupport::XmlMini.backend = 'LibXML'
This was only added in recent versions of Rails, I believe in 2.3.
Lately I’ve been doing a lot of API type work in Rails — both client and server. It mostly uses Rails’ default XML generation and consumption.
Along the way I’ve discovered that the default performance of XML and related things on Ruby and Rails is, shall we say, less than amazing. On the bright side, there are a number of ways to improve matters.
So, I’m going to do a series on improving the performance of Rails’ API-related stack.
I’ll start off with serialized columns in ActiveRecord.
I bought something on ebay this morning (a 60-year old book). That’s not particularly exciting. But in the process of trying to pay for it, I had several observations.
1. Finding and buying the item on ebay was fairly straight-forward. I’m not sure why the item didn’t show up in the main search results, but several acceptable options did show up in the “Here’s what people have in their stores” section. Good enough.
2. ebay continues to try to force everything through Paypal. I was going to do that this time anyway, but the lack of choice is below average.
3. ebay and Paypal are still run as separate sites. So when I click on checkout from ebay, it sends me over to Paypal. That’s the theory anyway. Instead I get a giant error message telling me that Paypal has experienced an error and that I should wait and try again.
So I wait. And try again. And it fails again.
I wait some more. Same error. “Odd,” I think.
Months ago (years maybe) I started configuring my web browsers to only allow cookies back to the source domain. This is mostly a privacy protection attempt as it keeps volumes of advertising cookies from being accepted.
On occasion some site exhibits bad behavior by relying on these cross-domain cookies. Wondering if ebay/Paypal is one of these errant sites, I dig into my browser’s cookies.
Sure enough, cookies that are shared between ebay.com and paypal.com have been refused. I enable just the select cookie and try the checkout again. Now it works.
While reviewing all the cookies, there were more than a dozen various advertising cookies that ebay also tried to set. This merely justifies my general decision to block such things.
The failure here is really two-fold. One is not having a better way to hand off the session data between domains — something in the url would seem appropriate enough.
The second is having an unhelpful, misleading error message.
4. Lastly, Paypal still, after all these years, refuses to let me set a credit card as my default payment method, instead forcing me to go through several clicks and multiple pages to override it for each purchase.
I’m reminding yet again why I buy from ebay and use Paypal so infrequently. It’s just a hassle.
One of the common questions in Rails land is how to disable the funny numbers at the end of images and CSS stylesheets. Let’s explore what exactly those numbers are, why they’re sometimes helpful, and how to turn them off when they’re not.