The permissions node in the Host's show action in APIv2 causes a lot of lookups to figure out the permissions. This has a high performance penalty (approx. 1 second).

https://github.com/theforeman/foreman/blob/develop/app/views/api/v2/hosts/show.json.rabl#L27-L32

This gist contains logs that show the slow queries:

https://gist.github.com/timogoebel/62ea0ac432b66f3e158863aea5bbc712#file-api-refactor-2-cleaned-txt-L766-L768