It sounds like you’re dealing with a challenging issue. Slow backend performance in WordPress can be caused by a variety of factors, and it can sometimes be difficult to pinpoint the exact cause. Since you’ve already tried disabling plugins and themes and optimizing the database, let’s consider some other potential causes and solutions:
- Server and Hosting Environment:
- Server Resources: Ensure that your server has adequate resources (CPU, RAM) to handle the load, especially since you’re running a multilingual site with a significant number of articles.
- PHP Version: Check if you’re using the latest PHP version. Newer versions of PHP are generally faster and more efficient.
- Database Server: Sometimes the database server (like MySQL) can be a bottleneck. Check its performance and configuration.
2. WordPress Configuration:
- Object Caching: Implement object caching if you haven’t already. Tools like Redis or Memcached can significantly improve backend performance.
- Transient API: Check if transients are being used efficiently. A large number of expired transients can slow down the database.
3. Detailed Profiling:
- Query Monitor: You mentioned using Query Monitor but not finding it helpful. It might be worth revisiting this tool. Look specifically for long-running queries, hooks that take a long time to execute, or any external calls that are made during backend operations.
- New Relic or Similar Tools: These can provide a more detailed insight into what’s happening on your server and can help identify slow functions, database queries, and external calls.
4. WordPress Heartbeat API:
- The Heartbeat API can cause high CPU usage. You might want to control the frequency of the Heartbeat API or disable it on certain pages.
5. File System Operations:
- Sometimes, slow file system operations can be a culprit. Check if there are any backup plugins or log file operations that are running in the background.
6. External Calls:
- Check if your site makes external API calls during backend operations, which can significantly slow down response times.
7. Error Logs:
- Review the WordPress and server error logs for any warnings or errors that might indicate underlying issues.
8. Compare Configurations:
- Since you mentioned that a similar site on the same server is running fine, compare the configurations of both sites meticulously. There might be subtle differences in wp-config.php settings, .htaccess rules, or even in the server configuration.
9. User Sessions and Transients:
- Investigate how user sessions and transients are handled. A large number of sessions or transients can slow down the site.
10. Content and Database Structure:
- Analyze if the structure of your posts, custom post types, or taxonomies is causing inefficiencies, especially since you have a large number of articles.
11. Network Issues:
- Sometimes the issue might be related to network latency between your location and the server, or between the server and external services it communicates with.
12. Testing in a Staging Environment:
- Consider setting up a staging environment where you can replicate the issue and experiment without affecting the live site.
Performance optimization can often be a process of trial and error. It’s important to make one change at a time and measure its impact before moving on to the next. This approach helps in identifying what exactly improves the performance.
