Change historical_data.date to timestamptz data type

Set the time and timezone of existing data to 12:00 in Time.zone since
the sidekiq-cron gem evaluates crons in the Rails timezones.

db/migrate/20201022094845_change_historical_data_date_type.rb

+# frozen_string_literal: true
+
+class ChangeHistoricalDataDateType < ActiveRecord::Migration[6.0]
+  DOWNTIME = false
+
+  def up
+    # historical_data only contains 1059 rows in gitlab.com. A new row is added
+    # once a day, so self-managed GitLab instances will probably have even less data.
+
+    # We're using `Time.zone.tzinfo.name` here because the sidekiq-cron gem
+    # evaluates crons against the timezone configured in Rails.
+    # The HistoricalDataWorker is set to run at 12 everyday.
+    execute(
+      <<SQL
+      ALTER TABLE historical_data ALTER COLUMN date TYPE timestamptz USING ((date + '12:00'::time) AT TIME ZONE '#{Time.zone.tzinfo.name}');
+SQL
+    )
+  end
+
+  def down
+    change_column :historical_data, :date, :date
+  end
+end

db/schema_migrations/20201022094845

+16b402740c6b1dd21908265085e516f63f8858424724ba97f46658e7bd5f7bf2
\ No newline at end of file

db/structure.sql

@@ -12699,7 +12699,7 @@ CREATE TABLE group_wiki_repositories (
 
 CREATE TABLE historical_data (
     id integer NOT NULL,
-    date date NOT NULL,
+    date timestamp with time zone NOT NULL,
     active_user_count integer,
     created_at timestamp without time zone,
     updated_at timestamp without time zone

ee/app/models/historical_data.rb

@@ -18,7 +18,7 @@ class HistoricalData < ApplicationRecord
 
     # HistoricalData.at(Date.new(2014, 1, 1)).active_user_count
     def at(date)
-      find_by(date: date)
+      find_by(date: date.all_day)
     end
 
     def max_historical_user_count(license: nil, from: nil, to: nil)

ee/changelogs/unreleased/271240-convert-to-timestamptz.yml

+---
+title: Change historical_data.date from date to timestamptz data type
+merge_request: 45893
+author:
+type: changed