WordPress Performance with HHVM

With Heroku-WP I hoped to lower the bar in getting WordPress up and running on a more modern tech stack. But what are the performance implications of running WordPress on such a modern set of technologies? Surely it’s faster but by how much and is the performance gains worth the trouble?

PHP vs HHVM

To answer that I’ve conducted a quick and dirty stress test of a sample WordPress site running under PHP and HipHop VM (HHVM) and found that the HHVM version loaded almost twice as fast and was able to serve over twice as many requests.

  Response Time Ok Responses Errors / Timeouts
Anon PHP 4.091 8,939 0.94%
Anon HHVM 2.122 18,308 0.00%
Change 48.1% 2.05X  
Auth PHP 20.688 457 74.17%
Auth HHVM 14.359 1,242 43.45%
Change 30.6% 2.72X  

In the numbers above anonymous requests represents hits to various pages without a WordPress logged in cookie which are eligible for Batcache caching whereas authorized requests are hits to the same pages with a login cookie thus bypassing page caching.

Test Methodology

To conduct this test I created a brand new Heroku instance based on the Heroku-WP template with the memcached addon installed. To populate the content I imported the WordPress Theme Unit Test after performing the initial setup. I then ran each permutation of the load test 5 times, flushing caches in between and averaged the results. When switching between PHP and HHVM I simply pushed a config change to composer.json and the boot script to toggle between the two interpreters.

To conduct the actual load test I used loader.io, (shameless referal link) a cloud based load generator with an insane 10,000 concurrent connection limit on the free account. (Quite generous when compared to the limit of 250 concurrent users on the free blitz.io account which I’ve used previously.) The free account of loader.io will only accept 2 URLs to test however with WordPress we can access most front-end pages via GET parameters passed to /index.php. Using this method and the following payload file I was able to have loader.io cycle through all posts, pages, categories, time based index pages, and the home page on the sample site for a more comprehensive sampling.

Finally, I ran all the tests for 60 seconds ramping up from 0 to 1,000 concurrent connections. I purposely excluded loading of static assets to place as much pressure as possible on PHP / HHVM for this synthetic stress test.

Conclusions

As expected, under high load MySQL is the real bottleneck, slowing down requests and causing errors due to hanging or killed queries. Caching was able to mitigate poor DB performance and bring page load times down by an order of magnitude for both PHP and HHVM.

Beyond that through simply turning on HHVM cut load times in half and appears to have allowed the server to better cope with multiple simultaneous slow requests piling up during times of high load. So if you have already installed a caching plugin and optimized your WordPress site running it on HHVM could potentially be an easy way to squeeze some more performance out of your setup.

05. September 2014 by Xiao
Categories: Uncategorized | Tags: , ,

Elasticsearch StatsD Plugin

If you’re running a multi-node Elasticsearch cluster checkout Automattic’s fork of the Elasticsearch StatsD Plugin for pushing cluster and node metrics to StatsD.

Elasticsearch, StatsD, and Grafana

At Automattic we’ve been using a set of Munin scripts to collect and aggregate Elasticsearch metrics via its native node & stats REST APIs. This method works relatively well giving us enough longitudinal information about the cluster and nodes to diagnose issues or test optimizations. That said, cluster monitoring with Munin at a 5 minute resolution leaves a lot to be desired.

First and foremost, our Elasticsearch cluster is spread across 3 data centers each with it’s own Munin instance. This makes collecting and aggregating even simple metrics like cluster wide load quite difficult. In addition, due to the polling nature of metrics collection with Munin we are limited to a somewhat corse resolution of 5 minutes. While this is good enough for looking at time series data over the course of a day or week it’s quite time-consuming to wait 5 or 10 minutes for graphs to update when deploying changes or testing performance optimizations.

We’ve already had some good experience instrumenting our PHP stack with StatsD and building dashboards with Grafana so reusing that infrastructure for Elasticsearch metrics seems like a good fit. Our fearless leader Barry suggested we tryout the Elasticsearch StatsD Plugin from Swoop Inc. however upon closer inspection we found that it does not deal with clustered Elasticsearch environments well and have yet to be updated to work with ES 1.x. So over the past week we’ve forked and rewritten much of it to suit our needs.

The Automattic Elasticsearch StatsD Plugin is designed to run on all nodes of a cluster and push metrics to StatsD on a configurable interval. Once installed and configured each node will send system metrics (e.g. CPU / JVM / network / etc.) about itself. Data nodes can also be configured to send metrics about the portion of the index stored on itself. Finally, the elected master of the cluster is responsible for sending aggregate cluster metrics about the index (documents / indexing operations / cache sizes / etc.). By default the plugin will send the total cluster aggregate as well as per index metrics for indices however granularity can be configured to report down to the individual shard level if so desired.

Check it out on GitHub: Elasticsearch StatsD Plugin.

11. August 2014 by Xiao
Categories: Uncategorized | Tags: ,

WordPress on NGINX + HHVM with Heroku Buildpacks

WordPress on NGINX + HHVM

It’s been a year since I last made any major changes to my WordPress on Heroku build and in tech years that’s a lifetime. Since then Heroku has released a new PHP buildpack with nginx and HHVM built in. Much progress have also been made both HHVM and WordPress to make both compatible with each other. So it seems like now is as good a time as any to update the stack this site is running on.

So without further ado I like to introduce:
Heroku WP — A template for HHVM powered WordPress served by nginx.

The Goal

There are numerous other templates out there for running WordPress on Heroku and my main goals for this templates are:

  1. It should be simple — use the default buildpack provided by Heroku so there’s no other 3rd party dependency to implicitly trust or to maintain.
  2. It should be fast — use the latest technologies available to squeeze every last ounce of performance out of each Heroku Dyno.
  3. It should be secure — security is not an add-on, admin pages should be secure by default and database connections needs to be encrypted.
  4. It should scale — just because we can serve millions of page hits a day off a single Heroku Dyno does not mean we’ll stop there. The template should be made with cloud architecture in mind so that the number of Dynos can scale up and down without breaking.

The Stack

Standing on the shoulder of giants I was able to use the latest Heroku buildpack and get WordPress running on:

  • NGINX — An event driven web server that was engineered for the modern day to replace Apache. This high performance web server is preferred by more top 1,000 sites then any other and it’s what’s used by the largest WordPress install out there, WordPress.com.
  • HHVM — HipHop Virtual Machine, a JIT (just in time) compiler developed by Facebook to run PHP scripts which when tested with WordPress showed up to a 2x improvement.

I have yet to run any statical analysis on performance however antidotally it feels a lot faster navigating WP admin and page generation times looks much better. I’m looking forward to running more tests and performance tuning this build in the coming weeks.


Update:
While still not a head-to-head test looking at the response times as reported by StatusCake for this site running on Heroku-WP and a mirror of this site that is running on the old Heroku LAMP stack with no load other then StatusCake pings shows a dramatic improvement:

Stack Max Min
LAMP 3,514 1,166
Heroku-WP 1,351 68

30. June 2014 by Xiao
Categories: DevOps | Tags: , , , ,

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