Redis provides an alternative caching backend for Drupal, taking that work off the database, which is vital for scaling to a larger number of logged-in users. It also provides a number of other nice features for develoeprs looking to use it to manage queues, or do custom caching of their own.

Particularly, it does a really great job of speeding up the content editing experience for logged in users quite a bit and makes Panopoly/the IPE much, much zippier with very little work.

See the docs here:

Configuration

request that Pantheon enable redis via a help ticket
install drupal redis module

In settings.php we drop in

/**
 * Perform web and drush operations on Pantheon
 * see http://helpdesk.getpantheon.com/customer/portal/articles/708588
 */
if (defined('PANTHEON_ENVIRONMENT')) {
 
  // Use Redis for caching on TEST and LIVE
  if (in_array(PANTHEON_ENVIRONMENT, array('test', 'live'))) {
    $conf['redis_client_interface'] = 'PhpRedis';
    $conf['cache_backends'][] = 'sites/all/modules/contrib/redis/redis.autoload.inc';
    $conf['cache_default_class'] = 'Redis_Cache';
    $conf['cache_prefix'] = array('default' => 'pantheon-redis');
    // Do not use Redis for cache_form (no performance difference).
    $conf['cache_class_cache_form'] = 'DrupalDatabaseCache';
    // Use Redis for Drupal locks (semaphore).
    $conf['lock_inc'] = 'sites/all/modules/contrib/redis/redis.lock.inc';
  }
 
}

to access Pantheon redis, you will need local command line tools.
this is easiest with homebrew on OS X:
```
$ brew install redis
```
or you can download at http://redis.io/download for all OSes.
To install with Docker:
docker pull shopigniter/redis-cli

Once install you will need to log in using the credentials from the pantheon dashboard
to flush the cache on DEV.
This is useful so that we have a baseline for testing speed gains and debugging.

$ redis-cli -h XXX.XXX.XXX.XXX -p XXXX -a xxxxxxxxxxxxxxxxxxxxxxxxxxx
> flushall

$ docker run -i -t --rm=true shopigniter/redis-cli -h XXX.XXX.XXX.XXX -p XXXX -a xxxxxxxxxxxxxxxxxxxxxxxxxxx
> flushall

External docs

Related articles

Page:

Conditional Caching - DEPRECATED
Page:

Redis cache configuration on Pantheon
Page:

Varnish Installation/Configuration

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