I Can’t enable Object Cache: Drop-in not installed

Try removing the wp-content/object-cache.php you have in place right now and then go to Settings > Redis > Enable Cache

Thank you @tillkruess,

Do you mean to delete the file object-cache.php?

Where this file is located?

I deleted the object-cache.php file and then enable Object Cache, the Drop-in was enabled for a minute and then turned off.

I have the Performance plugin installed by WordPress. Please see the new Diagnostics message below.

Status: Drop-in is invalid
Client:
Drop-in: Invalid
Disabled: No
PhpRedis: Not loaded
Relay: Not loaded
Predis: 2.0.3
Credis: Not loaded
PHP Version: 7.4.13
Plugin Version: 2.2.3
Redis Version: Unknown
Multisite: No
Metrics: Disabled
Metrics recorded: 0
Filesystem: Working
WP_REDIS_PLUGIN_PATH: “/opt/bitnami/apps/wordpress/htdocs/wp-content/plugins/redis-cache”
Drop-ins: [
“Performance Lab Server Timing Object Cache Drop-In v1 by WordPress Performance Team”
]

Please find a copy of my current object-cache.php file: What should be changed?

<?php
/**

• Plugin Name: Performance Lab Server Timing Object Cache Drop-In
• Plugin URI: https://github.com/WordPress/performance
• Description: Performance Lab drop-in to register Server-Timing metrics early. This is not a real object cache drop-in and will not override other actual object cache drop-ins.
• Version: 1
• Author: WordPress Performance Team
• Author URI: https://make.www.ads-software.com/performance/
• License: GPLv2 or later
• License URI: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
  *
• Object cache drop-in from Performance Lab plugin.
  *
• This drop-in is used, admittedly as a hack, to be able to measure server
• timings in WordPress as early as possible. Once a plugin is loaded, it is
• too late to capture several critical events.
  *
• This file respects any real object cache implementation the site may already
• be using, and it is implemented in a way that there is no risk for breakage.
  *
• If you do not want the Performance Lab plugin to place this file and thus be
• limited to server timings only from after plugins are loaded, you can remove
• this file and set the following constant (e.g. in wp-config.php):
  *
• define( ‘PERFLAB_DISABLE_OBJECT_CACHE_DROPIN’, true );
  *
• @package performance-lab
• @since 1.8.0
  */

// Set constant to be able to later check for whether this file was loaded.
define( ‘PERFLAB_OBJECT_CACHE_DROPIN_VERSION’, 1 );

/**

• Loads the Performance Lab Server-Timing API if available.
  *
• This function will short-circuit if the constant
• ‘PERFLAB_DISABLE_OBJECT_CACHE_DROPIN’ is set as true.
  *
• @since 1.8.0
  */
  function perflab_load_server_timing_api_from_dropin() {
  if ( defined( ‘PERFLAB_DISABLE_OBJECT_CACHE_DROPIN’ ) && PERFLAB_DISABLE_OBJECT_CACHE_DROPIN ) {
  return;
  } $plugins_dir = defined( ‘WP_PLUGIN_DIR’ ) ? WP_PLUGIN_DIR : WP_CONTENT_DIR . ‘/plugins’;
  $plugin_dir = $plugins_dir . ‘/performance-lab/’;
  if ( ! file_exists( $plugin_dir . ‘server-timing/load.php’ ) ) {
  $plugin_dir = $plugins_dir . ‘/performance/’;
  if ( ! file_exists( $plugin_dir . ‘server-timing/load.php’ ) ) {
  return;
  }
  } require_once $plugin_dir . ‘server-timing/class-perflab-server-timing-metric.php’;
  require_once $plugin_dir . ‘server-timing/class-perflab-server-timing.php’;
  require_once $plugin_dir . ‘server-timing/load.php’;
  require_once $plugin_dir . ‘server-timing/defaults.php’;
  }
  perflab_load_server_timing_api_from_dropin();

// Load the original object cache drop-in if present.
if ( file_exists( WP_CONTENT_DIR . ‘/object-cache-plst-orig.php’ ) ) {
require_once WP_CONTENT_DIR . ‘/object-cache-plst-orig.php’;
}

You need to turn off the server timing from Performance, it interferes with object caching.

Thank you @tillkruess for your support, much appreciated!

Yes, the issue was caused by the Performance Lab plugin overwriting the /wp-content/object-cache.php as documented here: https://www.ads-software.com/support/topic/plugin-overwrites-existing-third-party-wp-content-object-cache-php/

To solve this issue, I disabled the Performance Lab plugin, then activated Redis Object Cache and added this line:

define( 'PERFLAB_DISABLE_OBJECT_CACHE_DROPIN', true );

Then activated Performance Lab plugin and everything is working fine.

I have noticed that you just released a new version 2.2.4 to fix this issue (Prevent Perflab from overwriting the object cache drop-in), right?

Last, I want to confirm that I am all set here. Please find below the copy of my Diagnostics page after fixing the Drop-In issue and installing Redis on my Linux Debian server. Could you please confirm?

I am seeing that everything is working as expected, and the performance is great.

Do I still need to install PhpRedis as well?

Many Thanks!!!

Status: Connected
Client: Predis (v2.1.1)
Drop-in: Valid
Disabled: No
Ping: PONG
Errors: []
PhpRedis: Not loaded
Relay: Not loaded
Predis: 2.1.1
Credis: Not loaded
PHP Version: 7.4.13
Plugin Version: 2.2.4
Redis Version: 5.0.14
Multisite: No
Metrics: Enabled
Metrics recorded: 548
Filesystem: Working
Global Prefix: "wp_"
Blog Prefix: "wp_"
WP_REDIS_PLUGIN_PATH: "/opt/bitnami/apps/wordpress/htdocs/wp-content/plugins/redis-cache"
Global Groups: [
"blog-details",
"blog-id-cache",
"blog-lookup",
"global-posts",
"networks",
"rss",
"sites",
"site-details",
"site-lookup",
"site-options",
"site-transient",
"users",
"useremail",
"userlogins",
"usermeta",
"user_meta",
"userslugs",
"redis-cache",
"blog_meta"
]
Ignored Groups: [
"counts",
"plugins",
"themes",
"wordfence",
"wordfence-ls",
"WPForms_Entry_Handler"
]
Unflushable Groups: []
Groups Types: {
"blog-details": "global",
"blog-id-cache": "global",
"blog-lookup": "global",
"global-posts": "global",
"networks": "global",
"rss": "global",
"sites": "global",
"site-details": "global",
"site-lookup": "global",
"site-options": "global",
"site-transient": "global",
"users": "global",
"useremail": "global",
"userlogins": "global",
"usermeta": "global",
"user_meta": "global",
"userslugs": "global",
"redis-cache": "global",
"counts": "ignored",
"plugins": "ignored",
"themes": "ignored",
"blog_meta": "global",
"wordfence": "ignored",
"wordfence-ls": "ignored",
"WPForms_Entry_Handler": "ignored"
}
Drop-ins: [
"Redis Object Cache Drop-In v2.2.4 by Till Krüss"
]

Yes, you’re all set. Glad you found the the solution yourself.

Many Thanks, @tillkruess !

Keep up the good work.