Zend_Cache backend using Redis with full support for tags

This Zend_Cache backend allows you to use a Redis server as a central cache storage. Tags are fully supported without the use of TwoLevels cache so this backend is great for use on a single machine or in a cluster. Works with any Zend Framework project including all versions of Magento!

FEATURES

• Uses the phpredis PECL extension for best performance (requires master branch or tagged version newer than Aug 19 2011).
• Falls back to standalone PHP if phpredis isn't available using the Credis library.
• Tagging is fully supported, implemented using the Redis "set" and "hash" datatypes for efficient tag management.
• Key expiration is handled automatically by Redis.
• Supports unix socket connection for even better performance on a single machine.
• Supports configurable compression for memory savings. Can choose between gzip, lzf and snappy and can change configuration without flushing cache.
• Uses transactions to prevent race conditions between saves, cleans or removes causing unexpected results.
• Unit tested!

INSTALLATION (Magento)

1. Install redis (2.4+ required)
2. Install phpredis (optional)

• For 2.4 support you must use the "master" branch or a tagged version newer than Aug 19, 2011.
• phpredis is optional, but it is much faster than standalone mode
• phpredis does not support setting read timeouts at the moment (see pull request #260). If you receive read errors (“read error on connection”), this might be the reason.

3. Install this module using modman:

   • modman clone git://github.com/colinmollenhour/Cm_Cache_Backend_Redis.git

4. Edit app/etc/local.xml to configure:

   <!-- This is a child node of config/global -->
   <cache>
     <backend>Cm_Cache_Backend_Redis</backend>
     <backend_options>
       <server>127.0.0.1</server> <!-- or absolute path to unix socket -->
       <port>6379</port>
       <persistent></persistent> <!-- Specify unique string to enable persistent connections. E.g.: sess-db0; bugs with phpredis and php-fpm are known: https://github.com/nicolasff/phpredis/issues/70 -->
       <database>0</database> <!-- Redis database number; protection against accidental data loss is improved by not sharing databases -->
       <password></password> <!-- Specify if your Redis server requires authentication -->
       <force_standalone>0</force_standalone>  <!-- 0 for phpredis, 1 for standalone PHP -->
       <connect_retries>1</connect_retries>    <!-- Reduces errors due to random connection failures; a value of 1 will not retry after the first failure -->
       <read_timeout>10</read_timeout>         <!-- Set read timeout duration; phpredis does not currently support setting read timeouts -->
       <automatic_cleaning_factor>0</automatic_cleaning_factor> <!-- Disabled by default -->
       <compress_data>1</compress_data>  <!-- 0-9 for compression level, recommended: 0 or 1 -->
       <compress_tags>1</compress_tags>  <!-- 0-9 for compression level, recommended: 0 or 1 -->
       <compress_threshold>20480</compress_threshold>  <!-- Strings below this size will not be compressed -->
       <compression_lib>gzip</compression_lib> <!-- Supports gzip, lzf and snappy -->
     </backend_options>
   </cache>
   
   <!-- This is a child node of config/global for Magento Enterprise FPC -->
   <full_page_cache>
     <backend>Cm_Cache_Backend_Redis</backend>
     <backend_options>
       <server>127.0.0.1</server> <!-- or absolute path to unix socket -->
       <port>6379</port>
       <persistent></persistent> <!-- Specify unique string to enable persistent connections. E.g.: sess-db0; bugs with phpredis and php-fpm are known: https://github.com/nicolasff/phpredis/issues/70 -->
       <database>1</database> <!-- Redis database number; protection against accidental data loss is improved by not sharing databases -->
       <password></password> <!-- Specify if your Redis server requires authentication -->
       <force_standalone>0</force_standalone>  <!-- 0 for phpredis, 1 for standalone PHP -->
       <connect_retries>1</connect_retries>    <!-- Reduces errors due to random connection failures -->
       <lifetimelimit>57600</lifetimelimit>    <!-- 16 hours of lifetime for cache record -->
       <compress_data>0</compress_data>        <!-- DISABLE compression for EE FPC since it already uses compression -->
     </backend_options>
   </full_page_cache>
   

RELATED / TUNING

• The recommended "maxmemory-policy" is "volatile-lru". All tag metadata is non-volatile so it is recommended to use key expirations unless non-volatile keys are absolutely necessary so that tag data cannot get evicted. So, be sure that the "maxmemory" is high enough to accommodate all of the tag data and non-volatile data with enough room left for the volatile key data as well.
• Automatic cleaning is optional and not recommended since it is slow and uses lots of memory.
• Occasional (e.g. once a day) garbage collection is recommended if the entire cache is infrequently cleared and automatic cleaning is not enabled. The best solution is to run a cron job which does the garbage collection. (See "Example Garbage Collection Script" below.)
• Compression will have additional CPU overhead but may be worth it for memory savings and reduced traffic. For high-latency networks it may even improve performance. Use the Magento Cache Benchmark to analyze your real-world compression performance and test your system's performance with different compression libraries.
  • gzip — Slowest but highest compression. Most likely you will not want to use above level 1 compression.
  • lzf — Fastest compress, fast decompress. Install: sudo pecl install lzf
  • snappy — Fastest decompress, fast compress. Download and install: snappy and php-snappy
• Monitor your redis cache statistics with my modified munin plugin.
• Enable persistent connections. Make sure that if you have multiple configurations connecting the persistent string is unique for each configuration so that "select" commands don't cause conflicts.
• Use the stats.php script to inspect your cache to find oversized or wasteful cache tags.

Example Garbage Collection Script (Magento)

<?php PHP_SAPI == 'cli' or die('<h1>:P</h1>');
ini_set('memory_limit','1024M');
set_time_limit(0);
error_reporting(E_ALL | E_STRICT);
require_once 'app/Mage.php';
Mage::app()->getCache()->getBackend()->clean('old');
// uncomment this for Magento Enterprise Edition
// Enterprise_PageCache_Model_Cache::getCacheInstance()->getFrontend()->getBackend()->clean('old');

Release Notes

• November 19, 2012: Added read_timeout option. (Feature only supported in standalone mode, will be supported by phpredis when pull request #260 is merged)
• October 29, 2012: Added support for persistent connections. (Thanks samm-git!)
• October 12, 2012: Improved memory usage and efficiency of garbage collection and updated recommendation.
• September 17, 2012: Added connect_retries option (default: 1) to prevent errors from random connection failures.
• July 10, 2012: Added password authentication support.
• Mar 1, 2012: Using latest Credis_Client which adds auto-reconnect for standalone mode.
• Feb 15, 2012: Changed from using separate keys for data, tags and mtime to a single hash per key.
• Nov 10, 2011: Changed from using phpredis and redisent to Credis (which wraps phpredis). Implemented pipelining.

@copyright  Copyright (c) 2012 Colin Mollenhour (http://colin.mollenhour.com)
This project is licensed under the "New BSD" license (see source).