Support » Plugin: Redis Object Cache » Serialization of ‘SimpleXMLElement’ is not allowed

  • Resolved arthurnoerve


    Recently on the plugin list screen in the admin we get this error. It does not seem to affect anything else.

    Redis is running and it seems to be hitting from the Query Monitor stats.


    Error establishing a Redis connection

    Serialization of 'SimpleXMLElement' is not allowed

    This means that the connection information in your wp-config.php file are incorrect or that the Redis server is unreachable.

    • Are you sure you have the correct Redis host and port?
    • Are you sure Redis server is running?

    If you need help, please read the installation instructions.


    Status: Connected
    Client: Predis (v2.1.2)
    Drop-in: Valid
    Disabled: No
    Ping: PONG
    Errors: []
    PhpRedis: Not loaded
    Relay: Not loaded
    Predis: 2.1.2
    Credis: Not loaded
    PHP Version: 8.0.28
    Plugin Version: 2.4.1
    Redis Version: 6.0.16
    Multisite: No
    Metrics: Enabled
    Metrics recorded: 73
    Filesystem: Content directory is not writable.
    Global Prefix: "wp_"
    Blog Prefix: "wp_"
    WP_REDIS_PLUGIN_PATH: ".../wp-content/plugins/redis-cache"
    Global Groups: [
    Ignored Groups: [
    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",
        "theme_json": "ignored"
    Drop-ins: [
        "Query Monitor Database Class (Drop-in) v3.12.3 by John Blackbourn",
        "Redis Object Cache Drop-In v2.4.1 by Till Krüss"

Viewing 3 replies - 1 through 3 (of 3 total)
  • Plugin Author Till Krüss


    One of your plugins in throwing a SimpleXMLElement into the cache and that doesn’t work. They need to store raw XML instead.

    I have the exact same problem since a couple of days, also only when opening the (plugin) update page:

    Error establishing a Redis connection

    Serialization of 'SimpleXMLElement' is not allowed

    The error occurs on both the /update-core.php and the /wp-admin/plugins.php page. Redis seems to still work, but these pages cannot be accessed anymore.

    If indeed the cause is another plugin as Till mentioned, then the solution may be to disable all the plugins one by one to find the culprit (if anyone found it, please let us know). I didn’t have the opportunity yet to try this myself. Preferably this is of course handled/prevented in the Redis drop-in plugin itself.

    Update: the problem has suddenly disappeared! Didn’t really do anything, perhaps an auto-update of a plugin has fixed it, or my host changed something.

    Of course it would still be great if the drop-in plugin could prevent this problem from happening again. Not sure if that is possible though.

Viewing 3 replies - 1 through 3 (of 3 total)
  • You must be logged in to reply to this topic.