PERF: Reduce memory footprint of `Chat::AutoRemove::HandleCategoryUpdated.call` (#28381)

This is a follow up to ed11ee9d05.

In `Chat::AutoRemove::HandleCategoryUpdated`, we are currently loading
the related users record in batches and then handing it off to
`Chat::Action::CalculateMembershipsForRemoval.call`. However, we are
still seeing memory spike as a result of this.

This commit eliminates the allocation of `User` ActiveRecord objects until
absolutely necessary. `Chat::Action::CalculateMembershipsForRemoval.call` has been
updated to accept an ActiveRecord relation instead which allows us to
avoid the ActiveRecord allocations.

plugins/chat/app/services/chat/action/calculate_memberships_for_removal.rb

@@ -19,7 +19,7 @@ module Chat
     # out which of the users provided should have their [Chat::UserChatChannelMembership]
     # records removed based on those security cases.
     class CalculateMembershipsForRemoval
-      def self.call(scoped_users:, channel_ids: nil)
+      def self.call(scoped_users_query:, channel_ids: nil)
         channel_permissions_map =
           DB.query(<<~SQL, readonly: CategoryGroup.permission_types[:readonly])
           WITH category_group_channel_map AS (
@@ -59,12 +59,12 @@ module Chat
         scoped_memberships =
           Chat::UserChatChannelMembership
             .joins(:chat_channel)
-            .where(user: scoped_users)
+            .where(user_id: scoped_users_query.select(:id))
             .where(chat_channel_id: channel_permissions_map.map(&:channel_id))
 
         memberships_to_remove = []
+
         scoped_memberships.find_each do |membership|
-          scoped_user = scoped_users.find { |su| su.id == membership.user_id }
           channel_permission =
             channel_permissions_map.find { |cpm| cpm.channel_id == membership.chat_channel_id }
 
@@ -91,9 +91,12 @@ module Chat
           # At least one of the groups on the channel can create_post or
           # has full permission, remove the membership if the user is in none
           # of these groups.
-          if group_ids_with_write_permission.any? &&
-               !scoped_user.in_any_groups?(group_ids_with_write_permission)
-            memberships_to_remove << membership.id
+          if group_ids_with_write_permission.any?
+            scoped_user = scoped_users_query.where(id: membership.user_id).first
+
+            if !scoped_user&.in_any_groups?(group_ids_with_write_permission)
+              memberships_to_remove << membership.id
+            end
           end
         end
 

plugins/chat/app/services/chat/auto_remove/handle_category_updated.rb

@@ -59,16 +59,11 @@ module Chat
       end
 
       def remove_users_without_channel_permission(users:, category_channel_ids:)
-        memberships_to_remove = []
-
-        users.find_in_batches do |batch_users|
-          memberships_to_remove.concat(
-            Chat::Action::CalculateMembershipsForRemoval.call(
-              scoped_users: batch_users,
-              channel_ids: category_channel_ids,
-            ),
+        memberships_to_remove =
+          Chat::Action::CalculateMembershipsForRemoval.call(
+            scoped_users_query: users,
+            channel_ids: category_channel_ids,
           )
-        end
 
         return if memberships_to_remove.blank?
 

plugins/chat/app/services/chat/auto_remove/handle_destroyed_group.rb

@@ -98,7 +98,7 @@ module Chat
 
       def remove_users_without_channel_permission(scoped_users:)
         memberships_to_remove =
-          Chat::Action::CalculateMembershipsForRemoval.call(scoped_users: scoped_users)
+          Chat::Action::CalculateMembershipsForRemoval.call(scoped_users_query: scoped_users)
 
         return if memberships_to_remove.empty?
 

plugins/chat/app/services/chat/auto_remove/handle_user_removed_from_group.rb

@@ -77,7 +77,9 @@ module Chat
 
       def remove_from_private_channels(user:)
         memberships_to_remove =
-          Chat::Action::CalculateMembershipsForRemoval.call(scoped_users: [user])
+          Chat::Action::CalculateMembershipsForRemoval.call(
+            scoped_users_query: User.where(id: user.id),
+          )
 
         return if memberships_to_remove.empty?