The _transient_timeout_wc_product_loop_* entries in your WordPress database are related to WooCommerce transients. These entries are temporary cached data used by WooCommerce to optimize performance by avoiding repetitive calculations or database queries for certain functionalities, such as product loops or queries on your store.

When the wp_options table grows excessively due to these transient entries, it usually indicates an issue. Here are some possible causes:

1. Expired Transients Not Being Deleted

  • Normally, WordPress automatically cleans up expired transients. However, if this cleanup fails, old transient data can accumulate.
  • This might happen if:
    • The WordPress wp_cron system is disabled or misconfigured.
    • There is a conflict with a plugin that interferes with transient cleanup.

2. Excessive Transient Creation

  • A poorly written plugin or theme may be creating an excessive number of transient entries unnecessarily, causing the database to bloat.
  • WooCommerce customizations or extensions (such as those for product filtering, search, or AJAX-based product loading) might create transient entries with unique keys, leading to rapid growth.

3. Large Data Stored in Transients

  • Some transients might store unnecessarily large datasets, especially if plugins or custom code improperly cache heavy objects like full product queries or serialized arrays of data.

4. High Traffic Without Proper Caching

  • If your website experiences high traffic and lacks proper object caching (like Redis or Memcached), WooCommerce may generate and store many transients repeatedly.

5. Stale or Orphaned Transients

  • Sometimes, transients are not properly deleted after their associated processes complete. This can result in "orphaned" entries clogging the database.

How to Fix This Issue

1. Clean Up Old Transients

Run a database query to delete expired transients. You can use a plugin like WP-Optimize or Advanced Database Cleaner for this purpose, or execute the following SQL query directly in phpMyAdmin:

 
DELETE FROM wp_options WHERE option_name LIKE '_transient_%' AND option_name NOT LIKE '_transient_timeout_%';

2. Fix wp_cron Issues

  • Ensure that wp_cron is functioning properly:
    • Check if cron jobs are disabled in wp-config.php (look for DISABLE_WP_CRON).
    • Use a plugin like WP Crontrol to monitor and fix WordPress cron jobs.

3. Audit Plugins and Themes

  • Identify the source of excessive transients:
    • Temporarily disable plugins or switch to a default theme to isolate the cause.
    • Check for WooCommerce extensions or custom code that may be misusing transients.

4. Implement Object Caching

  • Set up object caching (e.g., Redis or Memcached) to handle transients more efficiently, reducing the load on your database.

5. Monitor Database Growth

  • Use database monitoring tools or plugins to track the growth of the wp_options table.
  • Consider setting up automatic cleanup for transients with plugins like Transients Manager.

Proactive Prevention

  • Regularly clean up your database using tools like WP-Optimize.
  • Update WordPress, WooCommerce, and plugins to their latest versions.
  • If the problem persists, consult with a developer to review your custom code or identify problematic plugins/extensions.