Nginx: What is server_names_hash_bucket_size?

What is server_names_hash_bucket_size.md

Background

While I'm learning how to use Nginx, I was instructed to update the server_names_hash_bucket_size (/etc/nginx/nginx.conf) value from 32 to 64, but I don't understand why should I increase the value to 64.

References

References that have been read so far:

• See the Server names, Optimization section.
• See setting up hashes
• See server_names_hash_bucket_size
• See server_names_hash_max_size

Key takeaways

• The default value of server_names_hash_bucket_size depends on the size of the processor’s cache line
• If a large number of server names are defined, or unusually long server names are defined, tuning the server_names_hash_max_size and server_names_hash_bucket_size directives at the http level may become necessary.
• If the default value of server_names_hash_bucket_size used at the server is not enough, means nginx complained with could not build the server_names_hash, you should increase server_names_hash_bucket_size: 32, the directive value should be increased to the next power of two (e.g. in this case to 64).
• If a large number of server names are defined, and nginx complained with the following error could not build the server_names_hash, you should increase either server_names_hash_max_size: 512 or server_names_hash_bucket_size: 32. try to set server_names_hash_max_size to a number close to the number of server names. Only if this does not help, or if nginx’s start time is unacceptably long, try to increase server_names_hash_bucket_size.
• The hash bucket size parameter is aligned to the size that is a multiple of the processor’s cache line size

Hear Hear!

Thanks for this. Can you also please the difference between the max and the bucket size ? It still confuses me.

Thanks for this!

Thanks for this!

√ Still useful. Thanks!

Well I raised both values to powers of 2 in steps till 512 and it did nothing.
Shortening very long local development domains worked.

ROLE-dashboard-COMPANY-TLD-docker-FRAMEWORK.local + 4 letters port => to something shorter fixed it for me.

Kind of odd nginx can't just resize this on the fly. Updating from 32 to 256 worked for me.

Thank you!

Thanks

Thank you!

Well I raised both values to powers of 2 in steps till 512 and it did nothing. Shortening very long local development domains worked.

ROLE-dashboard-COMPANY-TLD-docker-FRAMEWORK.local + 4 letters port => to something shorter fixed it for me.

With only 50 subdomains I had an NGinx crash with this error "could not build server_names_hash, you should increase server_names_hash_bucket_size: 64" just after adding a new one.

Investigating the issue : the last sub-domain added was 32 carracters long (total server_name with domain&tld = 48)

• if I shorten it to 30 (total 46) : it works.
• if I change server_names_hash_bucket_size from 64 to 128 : it works.

I don't understand why the length of server names is limited by this parameter, i'm still far from the official (RFC) limits for URLs. (and very very far from hash collisions)

I need to have a close look on this topic because in my case several subdomains are created arround a client choice for the "base name", so I need to know wich limit should I impose for this "base name".