Upstream sent too big header

Dave Hilditch

October 2, 2024

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Some users have reported that when they try to build the Super Speedy Search tables, they get a 502 Gateway error. When digging into this error, it turns out to be an ‘Upstream sent too big header’ error.

Deactivate Query Monitor

Query Monitor is a fantastic tool, but one side effect of having it active is that it increases the amount of data being transferred in your headers which in turn can cause this error.

Try deactivating Query Monitor and then try your Super Speedy Search build process again to see if the error goes away.

Fixing “Upstream sent too big header” Errors through config

If you’re encountering errors related to large headers or “upstream sent too big header”, and you wish to keep Query Monitor active (fair enough!) you need to adjust your web server’s configuration. The exact steps depend on your web server:

For Nginx Users:

Add or modify these lines in your Nginx configuration file (usually nginx.conf or in the server block of your site configuration):

fastcgi_buffers 16 32k;
fastcgi_buffer_size 64k;

For Apache Users:

If you’re using mod_proxy_fcgi, add or modify these lines in your Apache configuration:

ProxyIOBufferSize 64000

For LiteSpeed Users:

In your LiteSpeed WebAdmin console:

1. Go to Configuration → Server → Tuning.
2. Look for “Max Request Header Size” and increase its value (e.g., to 64K or higher if needed).

General Advice

1. After making changes, always restart your web server to apply the new configuration.
2. Start with moderate increases and test. If issues persist, gradually increase values.
3. Monitor server performance after changes to ensure stability.
4. If you’re on shared hosting or don’t have direct server access, contact your hosting provider for assistance with these changes.

Remember, these are general guidelines. The exact configuration might vary based on your specific setup and needs. If you’re unsure, consult with a system administrator or your hosting provider.