Title: Manual wp-cron Scheduling Causes PHP wp_cache_flush_runtime Error
Last modified: January 6, 2023
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# Manual wp-cron Scheduling Causes PHP wp_cache_flush_runtime Error
* Resolved [David Adams](https://wordpress.org/support/users/tictag/)
* (@tictag)
* [3 years, 5 months ago](https://wordpress.org/support/topic/manual-wp-cron-scheduling-causes-php-wp_cache_flush_runtime-error/)
* Rank Math was installed on a website I recently took ownership of. As far as
I know, there were no issues with it. I found that most wp-cron jobs were being
severely delayed due to a lack of site visitors so I disabled wp-cron scheduling`
define('DISABLE_WP_CRON', true);` and instead initiated wp-cron with a server`
crontab` job `wp cron event run --due-now, 0,30 * * * *` to forcibly initiate
wp-cron every 30 minutes, irrespective of site visitors.
* This works fine and now all wp-cron functions execute without delay.
* Since running wp-cron this way, however, the OS (Fedora Linux) `crontab` job
and WordPress debugging reports the following PHP Notice:
* `Notice: Function wp_cache_flush_runtime was called incorrectly. Your object cache implementation does not support flushing the in-memory runtime
cache. Please see Debugging in WordPress for more information. (This message was added in
version 6.1.0.) in /home/customer/www//public_html/wp-includes/functions.
php on line 5835`
* I traced this error back to a Rank Math wp-cron hook/action (I’m sorry, I don’t
remember which one). Deactivating Rank Math solved the problem.
* I would like to continue running Rank Math but also have a level of control over
wp-cron for the reasons stated above.
* Is this possible? Or is it one or the other?
* David.
Viewing 9 replies - 1 through 9 (of 9 total)
* Plugin Support [Rank Math Support](https://wordpress.org/support/users/rankmathteam/)
* (@rankmathteam)
* [3 years, 4 months ago](https://wordpress.org/support/topic/manual-wp-cron-scheduling-causes-php-wp_cache_flush_runtime-error/#post-16362445)
* Hello [@tictag](https://wordpress.org/support/users/tictag/),
* Thank you for contacting the support, and sorry for any inconvenience that might
have been caused due to that.
* Can you please try the following filter?
`function wp_cache_supports( $feature){
if ( $feature === 'flush_runtime' ) {return true;}return false;}
* There’s also a proposed change here:
[https://core.trac.wordpress.org/changeset/54448](https://core.trac.wordpress.org/changeset/54448)
* Hope that helps.
* [negapo](https://wordpress.org/support/users/negapo/)
* (@negapo)
* [3 years, 4 months ago](https://wordpress.org/support/topic/manual-wp-cron-scheduling-causes-php-wp_cache_flush_runtime-error/#post-16385334)
* We have the same problem, will you do anything at the plug-in side on future
versions to solve this?
* The above code isn’t a filter right, its a core WP function, should we overwrite
it?
* Thread Starter [David Adams](https://wordpress.org/support/users/tictag/)
* (@tictag)
* [3 years, 4 months ago](https://wordpress.org/support/topic/manual-wp-cron-scheduling-causes-php-wp_cache_flush_runtime-error/#post-16385873)
* Apologies for the delay is replying, I’ve had some personal matters to attend
to.
* I added the code above to a ‘Snippets’ snippet and received the following error
on activation:
* `The snippet has been deactivated due to an error on line 2:
Cannot redeclare
function wp_cache_supports.
* Please advise.
* Plugin Support [Rank Math Support](https://wordpress.org/support/users/rankmathteam/)
* (@rankmathteam)
* [3 years, 4 months ago](https://wordpress.org/support/topic/manual-wp-cron-scheduling-causes-php-wp_cache_flush_runtime-error/#post-16388205)
* Hello [@tictag](https://wordpress.org/support/users/tictag/),
The function we
shared is a default function since WordPress 6.1 so you would need to add this
to the following file and replace the current implementation: `wp-includes\cache-
compat.php`Don’t hesitate to get in touch if you have any other questions.
* Thread Starter [David Adams](https://wordpress.org/support/users/tictag/)
* (@tictag)
* [3 years, 4 months ago](https://wordpress.org/support/topic/manual-wp-cron-scheduling-causes-php-wp_cache_flush_runtime-error/#post-16389948)
* Do you not think that this information should have been included in your original
request, or were you expecting me to know this off-hand?
* I am not prepared to hack my WordPress installation just to do your troubleshooting
for you. This is a live site and I am not clever enough to be able to fix it
if your hack doesn’t work.
* Are you able to re-create this issue on your own test sites? If so, please just
let me know when you have a fix available. Until then, I will keep Rank Math
disabled whilst I look for an alternative.
* The clock is ticking.
* Thread Starter [David Adams](https://wordpress.org/support/users/tictag/)
* (@tictag)
* [3 years, 4 months ago](https://wordpress.org/support/topic/manual-wp-cron-scheduling-causes-php-wp_cache_flush_runtime-error/#post-16389953)
* p.s. This ticket has NOT been resolved!!
* Plugin Support [Rank Math Support](https://wordpress.org/support/users/rankmathteam/)
* (@rankmathteam)
* [3 years, 4 months ago](https://wordpress.org/support/topic/manual-wp-cron-scheduling-causes-php-wp_cache_flush_runtime-error/#post-16392518)
* Hello [@tictag](https://wordpress.org/support/users/tictag/),
* Sorry for the inconvenience caused. However, adding the filter to the file mentioned
before shouldn’t cause any issues with the site and will fix the issue.
* Having said that, we are working on a fix for this and will inform you here once
we release an update.
* We really appreciate your patience in the meantime.
* [negapo](https://wordpress.org/support/users/negapo/)
* (@negapo)
* [3 years, 4 months ago](https://wordpress.org/support/topic/manual-wp-cron-scheduling-causes-php-wp_cache_flush_runtime-error/#post-16403624)
* Just a side note, that’s not a filter, that’s a function, not a good idea to
change core functions but if this a temporary issue there is no problem. The
main thing is the last post, thats what we want to hear, this is not a environment
or installation issue, its a bug thats being addressed.
* Plugin Support [Rank Math Support](https://wordpress.org/support/users/rankmathteam/)
* (@rankmathteam)
* [3 years, 4 months ago](https://wordpress.org/support/topic/manual-wp-cron-scheduling-causes-php-wp_cache_flush_runtime-error/#post-16409928)
* Hello [@negapo](https://wordpress.org/support/users/negapo/),
* Yes, it was a temporary solution and the fix will be released in the upcoming
update of our plugin. You can keep an eye on our changelog to get notified: [https://rankmath.com/changelog/](https://rankmath.com/changelog/)
* Let us know if you need any other assistance.
Viewing 9 replies - 1 through 9 (of 9 total)
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## Tags
* [crontab](https://wordpress.org/support/topic-tag/crontab/)
* 9 replies
* 3 participants
* Last reply from: [Rank Math Support](https://wordpress.org/support/users/rankmathteam/)
* Last activity: [3 years, 4 months ago](https://wordpress.org/support/topic/manual-wp-cron-scheduling-causes-php-wp_cache_flush_runtime-error/#post-16409928)
* Status: resolved