Optimize suggestion usage data

Suggestions counter times out on gitlab.com. Adds an index to optimize
suggestion counters join. Also uses manual start/finish parameters for
the batch counting.

changelogs/unreleased/208890-optimize-notes-and-suggestion-counters.yml

+---
+title: Optimize suggestions counters
+merge_request: 26443
+author:
+type: performance

db/migrate/20200330132913_add_index_on_author_id_and_created_at_and_id_to_notes.rb

+# frozen_string_literal: true
+
+class AddIndexOnAuthorIdAndCreatedAtAndIdToNotes < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :notes, [:author_id, :created_at, :id]
+    remove_concurrent_index :notes, [:author_id, :created_at]
+  end
+
+  def down
+    add_concurrent_index :notes, [:author_id, :created_at]
+    remove_concurrent_index :notes, [:author_id, :created_at, :id]
+  end
+end

db/structure.sql

@@ -9519,7 +9519,7 @@ CREATE INDEX index_namespaces_on_type_partial ON public.namespaces USING btree (
 
 CREATE UNIQUE INDEX index_note_diff_files_on_diff_note_id ON public.note_diff_files USING btree (diff_note_id);
 
-CREATE INDEX index_notes_on_author_id_and_created_at ON public.notes USING btree (author_id, created_at);
+CREATE INDEX index_notes_on_author_id_and_created_at_and_id ON public.notes USING btree (author_id, created_at, id);
 
 CREATE INDEX index_notes_on_commit_id ON public.notes USING btree (commit_id);
 
@@ -12925,5 +12925,6 @@ COPY "schema_migrations" (version) FROM STDIN;
 20200326144443
 20200326145443
 20200330074719
+20200330132913
 \.
 

ee/lib/ee/gitlab/usage_data.rb

@@ -232,7 +232,10 @@ module EE
             protected_branches: distinct_count(::Project.with_protected_branches.where(time_period), :creator_id),
             remote_mirrors: distinct_count(::Project.with_remote_mirrors.where(time_period), :creator_id),
             snippets: distinct_count(::Snippet.where(time_period), :author_id),
-            suggestions: distinct_count(::Note.with_suggestions.where(time_period), :author_id)
+            suggestions: distinct_count(::Note.with_suggestions.where(time_period),
+                                        :author_id,
+                                        start: ::User.minimum(:id),
+                                        finish: ::User.maximum(:id))
           }
         end