Add missing expression indexes

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/280826

changelogs/unreleased/ab-add-missing-expression-indexes.yml

+---
+title: Add missing expression indexes
+merge_request: 47424
+author:
+type: performance

db/migrate/20201111152859_add_missing_expression_indexes.rb

+# frozen_string_literal: true
+
+class AddMissingExpressionIndexes < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  INDEXES = [
+    [:namespaces, :index_on_namespaces_lower_name, 'LOWER(name)'],
+    [:namespaces, :index_on_namespaces_lower_path, 'LOWER(path)'],
+    [:projects, :index_on_projects_lower_path, 'LOWER(path)'],
+    [:routes, :index_on_routes_lower_path, 'LOWER(path)'],
+    [:users, :index_on_users_lower_username, 'LOWER(username)'],
+    [:users, :index_on_users_lower_email, 'LOWER(email)']
+  ]
+
+  def up
+    # Those indexes had been introduced before, but they haven't been
+    # captured in structure.sql. For installations that already have it,
+    # this is a no-op - others will get it retroactively with
+    # this migration.
+
+    tables = Set.new
+
+    INDEXES.each do |(table, name, expression)|
+      unless index_name_exists?(table, name)
+        add_concurrent_index table, expression, name: name
+        tables.add(table)
+      end
+    end
+
+    # Rebuild statistics on affected tables only
+    tables.each do |table|
+      execute("ANALYZE #{table}")
+    end
+  end
+
+  def down
+    # no-op
+  end
+end

db/schema_migrations/20201111152859

+4c5baa6a09a339fac544f830d5ef822b1e7e4eae8431bd91df5113125accbc77
\ No newline at end of file

db/structure.sql

@@ -21326,12 +21326,24 @@ CREATE UNIQUE INDEX index_on_instance_statistics_recorded_at_and_identifier ON a
 
 CREATE INDEX index_on_label_links_all_columns ON label_links USING btree (target_id, label_id, target_type);
 
+CREATE INDEX index_on_namespaces_lower_name ON namespaces USING btree (lower((name)::text));
+
+CREATE INDEX index_on_namespaces_lower_path ON namespaces USING btree (lower((path)::text));
+
+CREATE INDEX index_on_projects_lower_path ON projects USING btree (lower((path)::text));
+
+CREATE INDEX index_on_routes_lower_path ON routes USING btree (lower((path)::text));
+
 CREATE UNIQUE INDEX index_on_segment_selections_group_id_segment_id ON analytics_devops_adoption_segment_selections USING btree (group_id, segment_id);
 
 CREATE UNIQUE INDEX index_on_segment_selections_project_id_segment_id ON analytics_devops_adoption_segment_selections USING btree (project_id, segment_id);
 
 CREATE INDEX index_on_segment_selections_segment_id ON analytics_devops_adoption_segment_selections USING btree (segment_id);
 
+CREATE INDEX index_on_users_lower_email ON users USING btree (lower((email)::text));
+
+CREATE INDEX index_on_users_lower_username ON users USING btree (lower((username)::text));
+
 CREATE INDEX index_on_users_name_lower ON users USING btree (lower((name)::text));
 
 CREATE INDEX index_open_project_tracker_data_on_service_id ON open_project_tracker_data USING btree (service_id);