Merge branch '22145-slow-search' into 'master'

Simplify projects, merge requests search queries

See merge request !10053

app/models/merge_request.rb

@@ -154,8 +154,10 @@ class MergeRequest < ActiveRecord::Base
   #
   # Returns an ActiveRecord::Relation.
   def self.in_projects(relation)
-    source = where(source_project_id: relation).select(:id)
-    target = where(target_project_id: relation).select(:id)
+    # unscoping unnecessary conditions that'll be applied
+    # when executing `where("merge_requests.id IN (#{union.to_sql})")`
+    source = unscoped.where(source_project_id: relation).select(:id)
+    target = unscoped.where(target_project_id: relation).select(:id)
     union  = Gitlab::SQL::Union.new([source, target])
 
     where("merge_requests.id IN (#{union.to_sql})")

app/models/project.rb

@@ -314,20 +314,15 @@ class Project < ActiveRecord::Base
       ntable  = Namespace.arel_table
       pattern = "%#{query}%"
 
-      projects = select(:id).where(
+      # unscoping unnecessary conditions that'll be applied
+      # when executing `where("projects.id IN (#{union.to_sql})")`
+      projects = unscoped.select(:id).where(
         ptable[:path].matches(pattern).
           or(ptable[:name].matches(pattern)).
           or(ptable[:description].matches(pattern))
       )
 
-      # We explicitly remove any eager loading clauses as they're:
-      #
-      # 1. Not needed by this query
-      # 2. Combined with .joins(:namespace) lead to all columns from the
-      #    projects & namespaces tables being selected, leading to a SQL error
-      #    due to the columns of all UNION'd queries no longer being the same.
-      namespaces = select(:id).
-        except(:includes).
+      namespaces = unscoped.select(:id).
         joins(:namespace).
         where(ntable[:name].matches(pattern))