Sometime on the 12th my site started to produce a series of PHP Fatal errors saying “Allowed memory size of 41943040 bytes exhausted.”. This was a bit of a surprise. It means that my memory limit was 40M, a lot lower than the expected value of 256M.
Other times the response was
[13-Jul-2016 02:54:59 UTC] PHP Fatal error: Unknown: Cannot use output buffering in output buffering display handlers in Unknown on line 0
Problem recovery
To recover from this problem I used ftp to rename Jetpack to Jetpack-f. I was then able to access the site.
Problem explanation
- The site was migrated from one host to another.
- The PHP version on the new host was 5.4.45.
- The memory_limit was set to
25M. - For PHP 5.3, 5.5 and 5.6 the memory_limit would have been
256M; a much nicer number. - By the time WordPress started up the memory limit became
40M. - It’s WordPress that sets this limit, depending on the site. For WPMS it’s
64M. See [api wp_initial_constants].
I’ve yet to track down the specific plugin/module combination that causes WP to exceed the 4OM limit.
Other notes
- My oik-bwtrace plugin reports the memory limit on its admin page.
- This is 256M, since WordPress sets it higher in admin pages. Using [hook admin_memory_limit] in wp-admin/admin.php.
- I’ve changed my [bw_code wp] shortcode to display the memory limit on the front-end.
- For this site the memory_limit has already been set by the hosting company to a high value.
WordPress 6.4.1. PHP: 8.2.13. Memory limit: 768M - I’m also experimenting with code that displays the current memory_limit in trace records produced by oik-bwtrace. They already optionally display current and peak memory usage, so adding the current memory limit is no big deal.