Add an partial index on push_rules(is_sample)

changelogs/unreleased-ee/add-pushrules-issample-partial-index2.yml

+---
+title: Add partial index on push_rules.is_sample
+merge_request:
+author:
+type: other

db/migrate/20170920091408_add_index_for_pushrules_is_sample.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddIndexForPushrulesIsSample < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  # When a migration requires downtime you **must** uncomment the following
+  # constant and define a short and easy to understand explanation as to why the
+  # migration requires downtime.
+  # DOWNTIME_REASON = ''
+
+  # When using the methods "add_concurrent_index", "remove_concurrent_index" or
+  # "add_column_with_default" you must disable the use of transactions
+  # as these methods can not run in an existing transaction.
+  # When using "add_concurrent_index" or "remove_concurrent_index" methods make sure
+  # that either of them is the _only_ method called in the migration,
+  # any other changes should go in a separate migration.
+  # This ensures that upon failure _only_ the index creation or removing fails
+  # and can be retried or reverted easily.
+  #
+  # To disable transactions uncomment the following line and remove these
+  # comments:
+  disable_ddl_transaction!
+
+  # Careful, on MySQL the where clause is ignored. We make the index
+  # on the same column as the WHERE clause (is_sample) even though
+  # this is generally a silly thing to do because that way on MySQL
+  # the resulting index on is_sample will still fix the same
+  # queries. It'll just waste space indexing all rows where is_sample
+  # is false as well. In this case there's only a single row where
+  # is_sample is true so having it be the index key is harmless.
+
+  def up
+    return if index_exists? :push_rules, :is_sample
+    add_concurrent_index(:push_rules, :is_sample, where: "is_sample")
+  end
+
+  def down
+    return unless index_exists? :push_rules, :is_sample
+    remove_concurrent_index(:push_rules, :is_sample, where: "is_sample")
+  end
+end

db/schema.rb

@@ -1618,6 +1618,7 @@ ActiveRecord::Schema.define(version: 20170928100231) do
     t.string "branch_name_regex"
   end
 
+  add_index "push_rules", ["is_sample"], name: "index_push_rules_on_is_sample", where: "is_sample", using: :btree
   add_index "push_rules", ["project_id"], name: "index_push_rules_on_project_id", using: :btree
 
   create_table "redirect_routes", force: :cascade do |t|