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Improving your site speed with Redis

Adding Redis to your application stack is a fantastic way to gain speed with existing applications. Many of our customers aren't running the latest and greatest new hotness NoSQL-using cloud thing. A lot of them port over a full stack of an existing applications that once only existed on bare metal servers, or use a hybrid environment with a big MySQL configuration on bare metal with web/app servers in the cloud.

In any case, we advise that customers use caching... EVERYWHERE. Adding Redis to your application stack can greatly improve site speeds when used as a cache.<!-- more -->

What's Redis?

From the "Introduction to Redis" page at

Redis is an open source, BSD licensed, advanced key-value store. It is often referred to as a data structure server since keys can contain strings, hashes, lists, sets and sorted sets. You can run atomic operations on these types, like appending to a string; incrementing the value in a hash; pushing to a list; computing set intersection, union and difference; or getting the member with highest ranking in a sorted set.

Want to try Redis? Check out

Why Redis?

There is a ton of debate out there on whether to use Redis or Memcached as a cache. Both are great, but Redis provides a few features over Memcached:

  • Persistence: if you restart the memcached service, you have to warm up your cache again.
  • Key/Value vs. Objects: Redis is more advanced in what it can store
  • Selective deletion of cached items

How do I set this up?

You can install Redis on a Cloud Server if you like, but I recommend setting up a Redis instance at RedisToGo. The instances are configured with Redis already, and RedisToGo makes Redis easy to scale. Other features of RedisToGo:

  • Graphs of connections and memory use
  • Monitoring notifications on memory use and connection limits
  • 1-click upgrades to scale
  • 1-click multi-zone redundancy.
  • Hourly backups
  • Paid plans persist data to disk on a RAM flush

Once Redis is installed and online, you need to configure your application to use it. The example below uses Predis, a PHP client library. There are plenty of clients to use with Redis, so you can pick and choose based on your preferred language.

The example below is from on a fantastic tutorial by Jim Westgren and is specific to WordPress-based sites, but WordPress specific code can be stripped out for use with just about any website. Enjoy!


    Author: Jim Westergren & Jeedo Aquino
    File: index-with-redis.php
    Updated: 2012-10-25

    This is a redis caching system for wordpress.
    see more here:

    Originally written by Jim Westergren but improved by Jeedo Aquino.

    some caching mechanics are different from jim's script which is summarized below:

    - cached pages do not expire not unless explicitly deleted or reset
    - appending a ?c=y to a url deletes the entire cache of the domain, only works when you are logged in
    - appending a ?r=y to a url deletes the cache of that url
    - submitting a comment deletes the cache of that page
    - refreshing (f5) a page deletes the cache of that page
    - includes a debug mode, stats are displayed at the bottom most part after </html>

    for setup and configuration see more here:

    use this script at your own risk. i currently use this albeit a slightly modified version
    to display a redis badge whenever a cache is displayed.


// change vars here
$cf = 1;            // set to 1 if you are using cloudflare
$debug = 0;         // set to 1 if you wish to see execution time and cache actions
$display_powered_by_redis = 1;  // set to 1 if you want to display a powered by redis message with execution time, see below

$start = microtime();   // start timing page exec

// if cloudflare is enabled
if ($cf) {
    if (isset($_SERVER['HTTP_CF_CONNECTING_IP'])) {

// from wp
define('WP_USE_THEMES', true);

// init predis
$redis = new Predis\Client('');

// init vars
$domain = $_SERVER['HTTP_HOST'];
$url = "http://".$_SERVER['HTTP_HOST'].$_SERVER['REQUEST_URI'];
$url = str_replace('?r=y', '', $url);
$url = str_replace('?c=y', '', $url);
$dkey = md5($domain);
$ukey = md5($url);

// check if page isn't a comment submission
(isset($_SERVER['HTTP_CACHE_CONTROL']) && $_SERVER['HTTP_CACHE_CONTROL'] == 'max-age=0') ? $submit = 1 : $submit = 0;

// check if logged in to wp
$cookie = var_export($_COOKIE, true);
$loggedin = preg_match("/wordpress_logged_in/", $cookie);

// check if a cache of the page exists
if ($redis->hexists($dkey, $ukey) && !$loggedin && !$submit && !strpos($url, '/feed/')) {

    echo $redis->hget($dkey, $ukey);
    $cached = 1;
    $msg = 'this is a cache';

// if a comment was submitted or clear page cache request was made delete cache of page
} else if ($submit || substr($_SERVER['REQUEST_URI'], -4) == '?r=y') {

    $redis->hdel($dkey, $ukey);
    $msg = 'cache of page deleted';

// delete entire cache, works only if logged in
} else if ($loggedin && substr($_SERVER['REQUEST_URI'], -4) == '?c=y') {

    if ($redis->exists($dkey)) {
        $msg = 'domain cache flushed';
    } else {
        $msg = 'no cache to flush';

// if logged in don't cache anything
} else if ($loggedin) {

    $msg = 'not cached';

// cache the page
} else {

    // turn on output buffering


    // get contents of output buffer
    $html = ob_get_contents();

    // clean output buffer
    echo $html;

    // Store to cache only if the page exist and is not a search result.
    if (!is_404() && !is_search()) {
        // store html contents to redis cache
        $redis->hset($dkey, $ukey, $html);
        $msg = 'cache is set';

$end = microtime(); // get end execution time

// show messages if debug is enabled
if ($debug) {
    echo $msg.': ';
    echo t_exec($start, $end);

if ($cached && $display_powered_by_redis) {
    // You should move this CSS to your CSS file and change the: float:right;margin:20px 0;
    echo "<style>#redis_powered{float:right;margin:20px 0;background:url( 10px no-repeat #fff;border:1px solid #D7D8DF;padding:10px;width:190px;}
    #redis_powered div{width:190px;text-align:right;font:10px/11px arial,sans-serif;color:#000;}</style>";
    echo "<a href=\"\" style=\"text-decoration:none;\"><div id=\"redis_powered\"><div>Page generated in<br/> ".t_exec($start, $end)." sec</div></div></a>";

// time diff
function t_exec($start, $end) {
    $t = (getmicrotime($end) - getmicrotime($start));
    return round($t,5);

// get time
function getmicrotime($t) {
    list($usec, $sec) = explode(" ",$t);
    return ((float)$usec + (float)$sec);



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