switch_to_blog() causes Fatal error on classic themes

[digberlin]

switch_to_blog() causes a fatal error "Allowed memory size of XXX bytes exhausted" on class-wpdb.php.
Does not happen when users are logged into the WordPress backend.
Tested on classic themes including Twenty Twenty-One. Twenty Twenty-Four seems to not be affected.
Tested on WP versions 6.5.2 and 6.5.3. WP version 6.4.x not affected.

[swissspidy]

Hi there and welcome to WordPress Trac!

Can you please share some code to reproduce this issue and where exactly you are using this code?

It sounds like your code is inadvertently creating some infinite loop or so, hence the memory issue.

[digberlin]

Replying to swissspidy:

Hi there and welcome to WordPress Trac!

Can you please share some code to reproduce this issue and where exactly you are using this code?

It sounds like your code is inadvertently creating some infinite loop or so, hence the memory issue.

Thank you swissspidy for looking into this.

In my themes, I switch to the main site on a multisite installation and get customs posts.

But this error occurs even when just calling switch_to_blog() and nothing else.

For testing, I added this

switch_to_blog(1);
restore_current_blog();

to functions.php on a clean Twenty Twenty-One Theme running on WP 5.6.3 with no plug-ins active. Also tested on both, local dev and live production installations.

Also tested on multiple other themes with same result:

Fatal error: Allowed memory size of 536870912 bytes exhausted (tried to allocate 8388608 bytes) in [redacted]/wordpress/wp-includes/class-wpdb.php on line 2320

When switching to any other site, like

switch_to_blog(7);
restore_current_blog();

adds an additional error

Fatal error: Allowed memory size of 536870912 bytes exhausted (tried to allocate 20480 bytes) in [redacted]/wordpress/wp-includes/class-wpdb.php on line 2320

Fatal error: Allowed memory size of 536870912 bytes exhausted (tried to allocate 20480 bytes) in [redacted]/wordpress/wp-includes/class-wp-fatal-error-handler.php on line 76

Twenty Twenty-Four is unaffected.
WP 6.4 is unaffected.

[swissspidy]

I still can't reproduce this with such a setup on 6.5. With multiple sites using Twenty Twenty-One, I added some code to functions.php and switching to a different site and getting some posts from there works just fine.

Maybe someone else has more luck; otherwise it sounds more like an issue with your specific setup.

[digberlin]

Replying to swissspidy:

I still can't reproduce this with such a setup on 6.5. With multiple sites using Twenty Twenty-One, I added some code to functions.php and switching to a different site and getting some posts from there works just fine.

Maybe someone else has more luck; otherwise it sounds more like an issue with your specific setup.

Where you logged into the WordPress backend while testing? The error does not occur when being logged in.

[swissspidy]

No errors on my setup, regardless if logged in or out.

[digberlin]

Found the culprit: object-cache.php installed by the Performance Lab plugin (Version 3.0.0; ​https://make.wordpress.org/performance/) which reamins in the wp-content folder even after uninstalling the plugin.

[swissspidy]

That's interesting. I ​filed an issue on the Performance Lab repository for the team to investigate. At the very least it should clean up after itself.

Closing this since it's not a core issue.

[swissspidy]

@digberlin Just a quick follow-up FYI: Performance Lab does remove the object cache drop-in upon plugin deactivation.