Merge branch 'sh-skip-sti-tables-reltuples' into 'master'

Fix counting of groups in admin dashboard

Closes gitlab-ee#7435

See merge request gitlab-org/gitlab-ce!26009

2 files changed, 26 insertions, 2 deletions

diff --git a/lib/gitlab/database/count/reltuples_count_strategy.rb b/lib/gitlab/database/count/reltuples_count_strategy.rb
index c3a674aeb7e..695f6fa766e 100644
--- a/lib/gitlab/database/count/reltuples_count_strategy.rb
+++ b/lib/gitlab/database/count/reltuples_count_strategy.rb
@@ -37,6 +37,22 @@ module Gitlab
 
         private
 
+        # Models using single-type inheritance (STI) don't work with
+        # reltuple count estimates. We just have to ignore them and
+        # use another strategy to compute them.
+        def non_sti_models
+          models.reject { |model| sti_model?(model) }
+        end
+
+        def non_sti_table_names
+          non_sti_models.map(&:table_name)
+        end
+
+        def sti_model?(model)
+          model.column_names.include?(model.inheritance_column) &&
+            model.base_class != model
+        end
+
         def table_names
           models.map(&:table_name)
         end
@@ -47,7 +63,7 @@ module Gitlab
           # Querying tuple stats only works on the primary. Due to load balancing, the
           # easiest way to do this is to start a transaction.
           ActiveRecord::Base.transaction do
-            get_statistics(table_names, check_statistics: check_statistics).each_with_object({}) do |row, data|
+            get_statistics(non_sti_table_names, check_statistics: check_statistics).each_with_object({}) do |row, data|
               model = table_to_model[row.table_name]
               data[model] = row.estimate
             end
diff --git a/lib/gitlab/database/count/tablesample_count_strategy.rb b/lib/gitlab/database/count/tablesample_count_strategy.rb
index fedf6ca4fe1..4fcd68b297d 100644
--- a/lib/gitlab/database/count/tablesample_count_strategy.rb
+++ b/lib/gitlab/database/count/tablesample_count_strategy.rb
@@ -48,12 +48,20 @@ module Gitlab
           end
         end
 
+        def where_clause(model)
+          return unless sti_model?(model)
+
+          "WHERE #{model.inheritance_column} = '#{model.name}'"
+        end
+
         def tablesample_count(model, estimate)
           portion = (TABLESAMPLE_ROW_TARGET.to_f / estimate).round(4)
           inverse = 1 / portion
           query = <<~SQL
             SELECT (COUNT(*)*#{inverse})::integer AS count
-            FROM #{model.table_name} TABLESAMPLE SYSTEM (#{portion * 100})
+            FROM #{model.table_name}
+            TABLESAMPLE SYSTEM (#{portion * 100})
+            #{where_clause(model)}
           SQL
 
           rows = ActiveRecord::Base.connection.select_all(query)