High CPU usage

If you are experiencing high CPU usage on your site, there are a few possible ways WP Rocket could cause this:

Pages are not cached

Make sure that WP Rocket is active and caches your pages:

How to check if WP Rocket is caching your pages

Preload

If your site has a lot of pages to preload and/or lacks enough server resources, preloading will cause a spike in CPU usage. If the spike causes a problem for your site you can try:

  • Limiting the number of sitemaps to be preloaded by un-checking WP Rocket's automatic sitemap detection from your SEO plugin (e.g. Yoast) and specifying only the most important ones to be preloaded:

  • Increasing the crawl interval
  • Deactivating sitemap-based preloading
  • If deactivating only sitemap-based preloading doesn't help, disable preload completely
  • Increasing the Cache Lifespan to avoid too frequent entire cache deletion and preloading
  • Setting up cron jobs to clear and preload the cache during periods of low server activity

    If disabling or limiting preload doesn't resolve the issue, try the steps below as well.

Remove Unused CSS

The process of generating Used CSS can cause high CPU usage.

You can use the available filters to decrease the number of Used CSS entries to process or to decrease the frequency of the processing, this should decrease the CPU usage in the cases where this optimization is causing it.

Use the rocket_rucss_pending_jobs_cron_rows_count filter to decrease the processing batch value. A lower value (default is 100 URLs) can help the server to work on fewer requests at a time.

If that doesn't help, you should decrease the frequency using the rocket_rucss_pending_jobs_cron_interval filter. By setting a higher value (default is 60 seconds), the server will have more time to rest between processing batches.

See this article for more details: Customize Remove Unused CSS parameters

In WP Rocket versions prior to 3.11, this feature scans your pages to collect and process the CSS and JS files. This can cause a spike in CPU usage, especially if there are a lot of files and pages to process. Try disabling this option and see if the CPU returns to normal.

If you see any of the following spiking in your usage logs, it points to this feature:

  • admin-ajax.php?action=rocket_saas_warmup
  • admin-ajax.php?action=rocket_rucss_warmup_resource_fetcher
  • WP_Rocket\Engine\Optimization\RUCSS\Warmup\Subscriber-collect_resources

Other file optimizations

Occasionally some of the other options on the File Optimization tab, such as Minify/Combine can cause high CPU usage in cases where your site has a lot of CSS or JS files. Try disabling these options and then monitor your CPU usage to see if it helps.

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