Improve performance of list of blocked domains by caching counts (mastodon#10374)

Author: Gargron

app/models/instance.rb

@@ -7,14 +7,18 @@ class Instance
 
   def initialize(resource)
     @domain         = resource.domain
-    @accounts_count = resource.accounts_count
+    @accounts_count = resource.is_a?(DomainBlock) ? nil : resource.accounts_count
     @domain_block   = resource.is_a?(DomainBlock) ? resource : DomainBlock.find_by(domain: domain)
   end
 
   def cached_sample_accounts
     Rails.cache.fetch("#{cache_key}/sample_accounts", expires_in: 12.hours) { Account.where(domain: domain).searchable.joins(:account_stat).popular.limit(3) }
   end
 
+  def cached_accounts_count
+    @accounts_count || Rails.cache.fetch("#{cache_key}/count", expires_in: 12.hours) { Account.where(domain: domain).count }
+  end
+
   def to_param
     domain
   end

app/views/admin/instances/index.html.haml

@@ -33,7 +33,7 @@
       %h4
         = instance.domain
         %small
-          = t('admin.instances.known_accounts', count: instance.accounts_count)
+          = t('admin.instances.known_accounts', count: instance.cached_accounts_count)
 
           - if instance.domain_block
             - if !instance.domain_block.noop?