Semiologic Cache Plugin For WordPress

The Semiologic Cache plugin for WordPress is a high performance cache for sites built using WP.

It requires PHP 5.0 to work; some features (the query cache) require as much as PHP 5.1. The niftier functionality is only available on servers with memcached installed. This is not available on shared hosts; but if you're on a VPS host, such as, you can take full advantage of it.

Activate the Semiologic Cache plugin, and browse Settings / Cache to use it. It implements the following:

  • A filesystem-based static cache of key pages, for ultimate caching when you experience massive amounts of requests on individual pages.
  • The semi-static cache, which can optionally be handled by memcache (allowing sites who live on multiple servers to avoid lags related to the filesystem).
  • A query-level cache for sites that use memcache; this significantly speeds things up for logged in users, provided they haven't authored private posts.
  • A persistent object-level cache, again using memcache. This speeds things up for much about everyone, by avoiding round trips to the database when none are needed.
  • An asset-level cache. This reduces the number of server requests per page by concatenating javascript and css files.
  • A gzip-level cache at the apache level, for servers that support mod_deflate. This significantly reduces the size of the files sent to end-users whose browser support it.


This package is part of Semiologic Pro, and is access-restricted.

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Frequently Asked Questions


The Semiologic forum is the best place to report issues.

Change Log

Version 2.8.2

  • Further optimization of css compression code.

Version 2.8.1

  • Css script could be moved to footer area impacting site presentation.

Version 2.8

  • Revamp of css and javascript file concatenating. Now working correctly especially footer scripts
  • Fix bug in handling of external css files only starting with url of / (no http: or https:)
  • Initial support for css compression. Seeing 10-25% file size improvements.
  • Caches flushed on WP upgrade

Version 2.7

  • Code refactoring
  • Silence 'Directory not empty' warning message in the cache-fs.php file
  • Further tweaking to fix invalid operation warning message in the cache-fs.php file
  • WP 3.9 compat

Version 2.6

  • Added ability to manually disable caching for a page.
  • Pages that include the Semiologic Contact Form widget are no longer cached. Caching conflicted with spam prevention techniques and was resulting in occasional false positives.
  • Fix invalid operation warning message in the cache-fs.php file
  • Updated htaccess caching rules

Version 2.5

  • Some Static Cache rules written to htaccess even if cached was turn off.
  • Fixed undefined variable in query_cache module
  • WP 3.8 compat

Version 2.4.1

  • Fix Undefined variable: wpdb in /wp-content/plugins/sem-cache/query-cache.php on line 526 warning

Version 2.4

  • Updated htaccess caching rules
  • www -> non-www or non-www -> www redirect rules added to htaccess is caching is turned on.
  • WP 3.6 compat
  • PHP 5.4 compat Important: Turn the cache off (Settings->Cache) then back on to force new server rules to be written

Version 2.3.6

  • Add Blackberry 10 User Agent detection

Version 2.3.5

  • Turn off auto enabling of cache

Version 2.3.4

  • Resolved unknown index warnings

Version 2.3.3

  • Fix: 3rd time the charm? wpdb::escape_by_ref() expected to be a reference message in query-cache.php

Version 2.3.2

  • Fix: wpdb::escape_by_ref() expected to be a reference message in query-cache.php
  • Silence warning message attempting to delete non-existant file
  • Fix misc. coding errors spotted by phpstorm

Version 2.3.1

  • Fix: Detection of mobile user agents that used mixed case failed

Version 2.3

  • Updated mobile agent detection Opera and Android Tablets
  • Asset cache is now cleared when Scripts & Meta is updated, theme is switched or plugins are activated/deactivated
  • Flush cache on Profile update due to Google+ Authorship
  • Fix warning message deleting non-existent file. Seems to be PHP 5.3 issue

Version 2.2

  • Fix static caching as WP_CACHE was not being written to wp-config.php
  • Add mod_expires and mod_mime sections.
  • Added more mod_deflate filters
  • Add cache control headers
  • Added auto-enable logic and source code switch to enable
  • Updated mobile User Agents

Version 2.1.1

  • WP 3.0.1 compat

Version 2.1

  • WP 3.0 compat

Version 2.0.1

  • Fix Apache 1.3 quirks
  • Improve safe_mode and open_basedir handling

Version 2.0

  • Complete rewrite
  • Add query cache, object cache, asset cache and gzip cache

Version 1.2.1

  • Improve handling of custom wp-content and plugin folders

Version 1.2

  • Don't super cache requests with a cookie or GET parameter