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Description

For sites concerned with high traffic, speed for logged-in users, or dynamic pageloads, a high-speed and persistent object cache is a must. You also need something that can scale across multiple instances of your application, so using local file caches or APC are out.

Redis is a great answer, and one we bundle on the Pantheon platform. This is our plugin for integrating with the cache, but you can use it on any self-hosted WordPress site if you have Redis. Install from WordPress.org or Github.

It’s important to note that a persistent object cache isn’t a panacea – a page load with 2,000 Redis calls can be 2 full seconds of object cache transactions. Make sure you use the object cache wisely: keep to a sensible number of keys, don’t store a huge amount of data on each key, and avoid stampeding frontend writes and deletes.

Go forth and make awesome! And, once you’ve built something great, send us feature requests (or bug reports). Take a look at the wiki for useful code snippets and other tips.

WP-CLI Commands

This plugin implements a variety of WP-CLI commands. All commands are grouped into the wp redis namespace.

$ wp help redis

NAME

  wp redis

SYNOPSIS

  wp redis <command>

SUBCOMMANDS

  cli         Launch redis-cli using Redis configuration for WordPress
  debug       Debug object cache hit / miss ratio for any page URL.
  enable      Enable WP Redis by creating the symlink for object-cache.php
  info        Provide details on the Redis connection.

Use wp help redis <command> to learn more about each command.

Contributing

See CONTRIBUTING.md for information on contributing.

Installation

This assumes you have a PHP environment with the required PhpRedis extension and a working Redis server (e.g. Pantheon). WP Redis also works with Predis via humanmade/wp-redis-predis-client.

Install object-cache.php to wp-content/object-cache.php with a symlink or by copying the file.

If you’re not running on Pantheon, edit wp-config.php to add your cache credentials, e.g.:

$redis_server = array(
    'host'     => '127.0.0.1',
    'port'     => 6379,
    'auth'     => '12345',
    'database' => 0, // Optionally use a specific numeric Redis database. Default is 0.
);

If your Redis server is listening through a sockt file instead, set its path on host parameter and change the port to null:

$redis_server = array(
    'host'     => '/path/of/redis/socket-file.sock',
    'port'     => null,
    'auth'     => '12345',
    'database' => 0, // Optionally use a specific numeric Redis database. Default is 0.
);

Engage thrusters: you are now backing WP’s Object Cache with Redis.
(Optional) To use the wp redis WP-CLI commands, activate the WP Redis plugin. No activation is necessary if you’re solely using the object cache drop-in.
(Optional) To use the same Redis server with multiple, discreet WordPress installs, you can use the WP_CACHE_KEY_SALT constant to define a unique salt for each install.
(Optional) To use true cache groups, with the ability to delete all keys for a given group, register groups with wp_cache_add_redis_hash_groups(), or define the WP_REDIS_USE_CACHE_GROUPS constant to true to enable with all groups. However, when enabled, the expiration value is not respected because expiration on group keys isn’t a feature supported by Redis.
(Optional) On an existing site previously using WordPress’ transient cache, use WP-CLI to delete all (%_transient_%) transients from the options table: wp transient delete-all. WP Redis assumes responsibility for the transient cache.
(Optional) To use Relay instead of PhpRedis as the client define the WP_REDIS_USE_RELAY constant to true. For support requests, please use Relay’s GitHub discussions.

FAQ

Why would I want to use this plugin?

If you are concerned with the speed of your site, backing it with a high-performance, persistent object cache can have a huge impact. It takes load off your database, and is faster for loading all the data objects WordPress needs to run.

How does this work with other caching plugins?

This plugin is for the internal application object cache. It doesn’t have anything to do with page caches. On Pantheon you do not need additional page caching, but if you are self-hosted you can use your favorite page cache plugins in conjunction with WP Redis.

How do I disable the persistent object cache for a bad actor?

A page load with 2,000 Redis calls can be 2 full seonds of object cache transactions. If a plugin you’re using is erroneously creating a huge number of cache keys, you might be able to mitigate the problem by disabling cache persistency for the plugin’s group:

wp_cache_add_non_persistent_groups( array( 'bad-actor' ) );

This declaration means use of wp_cache_set( 'foo', 'bar', 'bad-actor' ); and wp_cache_get( 'foo', 'bad-actor' ); will not use Redis, and instead fall back to WordPress’ default runtime object cache.

Why does the object cache sometimes get out of sync with the database?

There’s a known issue with WordPress alloptions cache design. Specifically, a race condition between two requests can cause the object cache to have stale values. If you think you might be impacted by this, review this GitHub issue for links to more context, including a workaround.

Where do I report security bugs found in this plugin?

Please report security bugs found in the source code of the WP Redis plugin through the Patchstack Vulnerability Disclosure Program. The Patchstack team will assist you with verification, CVE assignment, and notify the developers of this plugin.

Reviews

mandrael January 15, 2024 2 replies

Great free Redis plugin which even does not need to be kept installed. Just install and copy object-cache.php to wp-content. Then add a wp-config setting (after installing redis on your server) and you are good to go. Check with WP health on dashboard. Thanks to the developers!

Jeremy October 16, 2023

Great plugin. I’m evaluating it now as a backend Redis cache. However, installation was not straightforward or clear. I wish it was automatic. However, the manual install requires copying a file manually. If you run multiple WordPress sites on a self-hosted install, you must also make sure to edit the object-cache.php file and add a cache salt key or you will get errors. Once these are resolved, it seems to be functioning well. 4 stars for the excellent plugin.-1 for the difficult installation. I wish it were more straightforward.

FLORIAN PRACHE January 24, 2023

Congratulations to the developers of this free extension, works wonderfully without wasting time, a performance gain examplary on the Back-Office side with a client site with 40 extensions. 10s -> 1s Keep it up folks 😉

strarsis June 4, 2021

Well maintained, free and open source plugin which only job is to implement a redis-based object cache, which does it well.

ejbt12 April 29, 2021

It is working great!, How does this plugin differs with “Redis Object Cache” since you don’t offer premium subscription for the plugin? drop-in based, no need to activate the plugin, just follow the GIT Instruction. Currently on my staging environment for testing.

nsbrown February 21, 2021

If you have a specific environment then put aside a day, if you’re not comfortable with ssh then don’t do it.

Read all 18 reviews

Contributors & Developers

“WP Redis” is open source software. The following people have contributed to this plugin.

Translate “WP Redis” into your language.

Interested in development?

Browse the code, check out the SVN repository, or subscribe to the development log by RSS.

Changelog

1.4.4 (November 27, 2023)

Updates Pantheon WP Coding Standards to 2.0 [#445]
Handle duplicate keys in get_multiple function [#448] (props @souptik)

1.4.3 (June 26, 2023)

Bug fix: Fixes assumption that CACHE_PORT & CACHE_PASSWORD are Set. [428] (props @tnolte)
Adds WP.org validation GitHub action [#435]
Bug fix: Fixes incorrect order of array_replace_recursive and other issues [434] (props @timnolte)
Bug fix: Replace use of wp_strip_all_tags in object-cache.php [434] (props @timnolte)
Bug fix: Don’t strip tags from the cache password. [434] (props @timnolte)

1.4.2 (May 15, 2023)

Bug fix: Removes exception loop caused by esc_html in _exception_handler() [421]

1.4.1 (May 11, 2023)

Bug fix: wp_cache_flush_runtime should only clear the local cache [413]

1.4.0 (May 9, 2023)

Add support for flush_runtime and flush_group functions [#405]
Add pantheon-wp-coding-standards [#400]
Update CONTRIBUTING.MD [#406]
Update Composer dependencies [#401]

1.3.5 (April 6, 2023)

Bump tested up to version to 6.2
Update Composer dependencies [#394]

1.3.4 (March 7, 2023)

Set missing_redis_message if Redis service is not connected [#391].

1.3.3 (February 28, 2023)

Add PHP 8.2 support [#388].
Remove Grunt, add valid license to Composer file [#387].
Update Composer dependencies [#384] [#385].

1.3.2 (December 5, 2022)

Fix broken wp_cache_supports function [#382].

1.3.1 (December 2, 2022)

Declare wp_cache_supports function and support features. [#378]
Make dependabot target develop branch for PRs. [#376]

1.3.0 (November 29, 2022)

Added CONTRIBUTING.MD and GitHub action to automate deployments to wp.org. [#368]

1.2.0 (February 17, 2022)

Adds support for Relay via WP_REDIS_USE_RELAY constant [#344].

1.1.4 (October 21, 2021)

Fixes some faulty logic in WP_REDIS_IGNORE_GLOBAL_GROUPS check [#333].

1.1.3 (October 21, 2021)

Supports a WP_REDIS_IGNORE_GLOBAL_GROUPS constant to prevent groups from being added to global caching group [#331].

1.1.2 (March 24, 2021)

Applies logic used elsewhere to fall back to $_SERVER in wp_redis_get_info() [#316].

1.1.1 (August 17, 2020)

Returns cache data in correct order when using wp_cache_get_multiple() and internal cache is already primed [#292].

1.1.0 (July 13, 2020)

Implements wp_cache_get_multiple() for WordPress 5.5 [#287].
Bails early when connecting to Redis throws an Exception to avoid fatal error [285].

1.0.1 (April 14, 2020)

Adds support for specifying Redis database number from environment/server variables [#273].

1.0.0 (March 2, 2020)

Plugin is stable.

0.8.3 (February 24, 2020)

Fixes wp redis cli by using proc_open() directly, instead of WP_CLI::launch() [#268].

0.8.2 (January 15, 2020)

Catches exceptions when trying to connect to Redis [#265].

0.8.1 (January 10, 2020)

Adds WP_REDIS_DEFAULT_EXPIRE_SECONDS constant to set default cache expire value [#264].

0.8.0 (January 6, 2020)

Uses flushdb instead of flushAll to avoid flushing the entire Redis instance [#259].

0.7.1 (December 14, 2018)

Better support in wp_cache_init() for drop-ins like LudicrousDB [#231].
Cleans up PHPCS issues.

0.7.0 (August 22, 2017)

Adds filterable connection methods to permit use of Predis. See humanmade/wp-redis-predis-client for more details.

0.6.2 (June 5, 2017)

Bug fix: Preserves null values in internal cache.
Bug fix: Converts numeric values to their true type when getting.

0.6.1 (February 23, 2017)

Bug fix: correctly passes an empty password to redis-cli.
Variety of improvements to the test suite.

0.6.0 (September 21, 2016)

Introduces three new WP-CLI commands: wp redis debug to display cache hit/miss ratio for any URL; wp redis info to display high-level Redis statistics; wp redis enable to create the object-cache.php symlink.
Permits a Redis database to be defined with $redis_server['database'].
Introduces wp_cache_add_redis_hash_groups(), which permits registering specific groups to use Redis hashes, and is more precise than our existing WP_REDIS_USE_CACHE_GROUPS constant.

0.5.0 (April 27, 2016)

Performance boost! Removes redundant exists call from wp_cache_get(), which easily halves the number of Redis calls.
Uses add_action() and $wpdb in a safer manner for compatibility with Batcache, which loads the object cache before aforementioned APIs are available.
For debugging purposes, tracks number of calls to Redis, and includes breakdown of call types.
Adds a slew of more explicit test coverage against existing features.
For consistency with the actual Redis call, calls del instead of delete.
Bug fix: If a group isn’t persistent, don’t ever make an exists call against Redis.

0.4.0 (March 23, 2016)

Introduces wp redis-cli, a WP-CLI command to launch redis-cli with WordPress’ Redis credentials.
Bug fix: Ensures fail back mechanism works as expected on multisite, by writing to sitemeta table instead of the active site’s options table.
Bug fix: Uses ‘default’ as the default cache group, mirroring WordPress core, such that $wp_object_cache->add( 'foo', 'bar' ) === wp_cache_add( 'foo', 'bar' ).

0.3.0 (February 11, 2016)

Introduces opt-in support for Redis cache groups. Enable with define( 'WP_REDIS_USE_CACHE_GROUPS', true );. When enabled, WP Redis persists cache groups in a structured manner, instead of hashing the cache key and group together.
Uses PHP_CodeSniffer and WordPress Coding Standards sniffs to ensure WP Redis adheres to WordPress coding standards.
Bug fix: Permits use of a Unix socket in $redis_server['host'] by ensuring the supplied $port is null.

0.2.2 (November 24, 2015)

Bug fix: use INSERT IGNORE INTO instead of INSERT INTO to prevent SQL errors when two concurrent processes attempt to write failback flag at the same time.
Bug fix: use E_USER_WARNING with trigger_error().
Bug fix: catch Exceptions thrown during authentication to permit failing back to internal object cache.

0.2.1 (November 17, 2015)

Bug fix: prevent SQL error when $wpdb->options isn’t yet initialized on multisite.

0.2.0 (November 17, 2015)

Gracefully fails back to the WordPress object cache when Redis is unavailable or intermittent. Previously, WP Redis would hard fatal.
Triggers a PHP error if Redis goes away mid-request, for you to monitor in your logs. Attempts one reconnect based on specific error messages.
Forces a flushAll on Redis when Redis comes back after failing. This behavior can be disabled with the WP_REDIS_DISABLE_FAILBACK_FLUSH constant.
Show an admin notice when Redis is unavailable but is expected to be.

0.1

Initial commit of working code for the benefit of all.