Changing the locale set on a maching running Postgres

I keep rediscovering that Postgres uses the system locale and timezone database, despite having read other people’s woes.

I changed the locale in my NixOS configuration from en_US to en_GB to appease the spell checker on my desktop. When I deployed this updated configuration to one of my servers, all my services immediately fell over.

I had the sense to look at journalctl right away which made it very apparent what the problem was:

Oct 29 18:27:00 wailord postgres[3593]: [3593] FATAL:  database locale is incompatible with operating system
Oct 29 18:27:00 wailord postgres[3593]: [3593] DETAIL:  The database was initialized with LC_COLLATE "en_US.UTF-8",  which is not recognized by setlocale().
Oct 29 18:27:00 wailord postgres[3593]: [3593] HINT:  Recreate the database with another locale or install the missing locale.
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(Yes my server is called wailord, I was loving Cobblemon when it was provisioned)

The solution was to simply add en_US back to i18n.supportedLocales and a rebuild fixed everything right up.