Restore memoization to base query and add a batch base query method

app/models/cycle_analytics.rb

@@ -7,8 +7,13 @@ class CycleAnalytics
   end
 
   def all_medians_per_stage
-    STAGES.each_with_object({}) do |stage_name, hsh|
-      hsh[stage_name] = self[stage_name].median
+    medians_per_stage = {}
+
+    # We only need this data for Postgres instances
+    return medians_per_stage if Gitlab::Database.mysql?
+
+    STAGES.each do |stage_name|
+      medians_per_stage[stage_name] = self[stage_name].median
     end
   end
 

app/serializers/analytics_stage_entity.rb

@@ -7,6 +7,6 @@ class AnalyticsStageEntity < Grape::Entity
   expose :description
 
   expose :median, as: :value do |stage|
-    stage.median && !stage.median.blank? ? distance_of_time_in_words(stage.median) : nil
+    distance_of_time_in_words(stage.median) if stage.median && !(stage.median.blank? || stage.median.zero?)
   end
 end

lib/gitlab/cycle_analytics/base_query.rb

@@ -7,14 +7,15 @@ module Gitlab
 
       private
 
-      def base_query(project_ids = nil)
-        stage_query(project_ids)
+      def base_query
+        @base_query ||= stage_query([@project.id])
       end
 
-      def stage_query(project_ids = nil)
+      def stage_query(project_ids)
         query = mr_closing_issues_table.join(issue_table).on(issue_table[:id].eq(mr_closing_issues_table[:issue_id]))
           .join(issue_metrics_table).on(issue_table[:id].eq(issue_metrics_table[:issue_id]))
-          .where(issue_table[:project_id].in(project_ids || @project.id)) # rubocop:disable Gitlab/ModuleWithInstanceVariables
+          .project(issue_table[:project_id].as("project_id"))
+          .where(issue_table[:project_id].in(project_ids)) # rubocop:disable Gitlab/ModuleWithInstanceVariables
           .where(issue_table[:created_at].gteq(@options[:from])) # rubocop:disable Gitlab/ModuleWithInstanceVariables
 
         # Load merge_requests
@@ -22,7 +23,6 @@ module Gitlab
           .on(mr_table[:id].eq(mr_closing_issues_table[:merge_request_id]))
           .join(mr_metrics_table)
           .on(mr_table[:id].eq(mr_metrics_table[:merge_request_id]))
-          .project(issue_table[:project_id].as("project_id"))
 
         query
       end

lib/gitlab/cycle_analytics/base_stage.rb

@@ -29,7 +29,7 @@ module Gitlab
           # We compute the (end_time - start_time) interval, and give it an alias based on the current
           # cycle analytics stage.
           interval_query = Arel::Nodes::As.new(cte_table,
-            subtract_datetimes(base_query(project_ids), start_time_attrs, end_time_attrs, name.to_s))
+            subtract_datetimes(stage_query(project_ids), start_time_attrs, end_time_attrs, name.to_s))
 
           median_datetimes(cte_table, interval_query, name, :project_id)&.each do |project_id, median|
             loader.call(project_id, median)

lib/gitlab/cycle_analytics/production_helper.rb

@@ -1,7 +1,7 @@
 module Gitlab
   module CycleAnalytics
     module ProductionHelper
-      def stage_query(project_ids = nil)
+      def stage_query(project_ids)
         super(project_ids)
           .where(mr_metrics_table[:first_deployed_to_production_at]
           .gteq(@options[:from])) # rubocop:disable Gitlab/ModuleWithInstanceVariables

lib/gitlab/cycle_analytics/test_stage.rb

@@ -25,7 +25,7 @@ module Gitlab
         _("Total test time for all commits/merges")
       end
 
-      def stage_query(project_ids = nil)
+      def stage_query(project_ids)
         if @options[:branch]
           super(project_ids).where(build_table[:ref].eq(@options[:branch]))
         else