Adds index on issues nested set columns.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@3578 e93f8b46-1217-0410-a6f0-8f06a7374b81

db/migrate/20100313171051_add_index_on_issues_nested_set.rb

@@ -0,0 +1,9 @@
+class AddIndexOnIssuesNestedSet < ActiveRecord::Migration
+  def self.up
+    add_index :issues, [:root_id, :lft, :rgt]
+  end
+
+  def self.down
+    remove_index :issues, [:root_id, :lft, :rgt]
+  end
+end