@hatabowyou おーっ!よかったです。こちらでお役に立てそうなことがあればまたお知らせください。
With three less threads for Sidekiq, (v90) this instance seems to be happier with memory. The spike in response time corresponds to a spike in traffic. https://mastodon.zunda.ninja/media/xDQGSO9DUusQFDi6eRI
$ heroku pg:info DATABASE_URL
=== DATABASE_URL, PG_HOBBY_BASIC_URL
Plan: Hobby-basic
Status: Available
Connections: 7/20
PG Version: 9.6.1
Created: 2017-04-20 18:31 UTC
Data Size: 78.2 MB
Tables: 29
Rows: 99777/10000000 (In compliance)
WAT
Unable to load application: LoadError: /tmp/build_08f19d87ce81840c613aa72c33dd4684/zunda-mastodon-7dc2edb/vendor/bundle/ruby/2.4.0/gems/nokogiri-1.7.2/ext/nokogiri/nokogiri.so: cannot open shared object file: No such file or directory - /app/vendor/bundle/ruby/2.4.0/gems/nokogumbo-1.4.12/lib/nokogumboc.so
$ heroku repo:purge_cache
and redploying... nope. Something funny is happening here.
$ cd /app/vendor/bundle/ruby/2.4.0/gems/nokogumbo-1.4.12/lib
$ ldd nokogumboc.so | grep nokogiri
/tmp/build_90c35b6741220e3f9f7136f4f509b231/zunda-mastodon-7dc2edb/vendor/bundle/ruby/2.4.0/gems/nokogiri-1.7.2/ext/nokogiri/nokogiri.so => not found