Add temporary partial index to speed up the migration

Closes #32469

db/post_migrate/20170503004427_upate_retried_for_ci_build.rb

@@ -8,6 +8,7 @@ class UpateRetriedForCiBuild < ActiveRecord::Migration
   def up
     disable_statement_timeout
 
+    with_temporary_partial_index do
       latest_id = <<-SQL.strip_heredoc
         SELECT MAX(ci_builds2.id)
           FROM ci_builds ci_builds2
@@ -23,7 +24,20 @@ class UpateRetriedForCiBuild < ActiveRecord::Migration
         query.where(table[:retried].eq(nil))
       end
     end
+  end
 
   def down
   end
+
+  def with_temporary_partial_index
+    if Gitlab::Database.postgresql?
+      execute 'CREATE INDEX CONCURRENTLY IF NOT EXISTS index_for_ci_builds_retried_migration ON ci_builds (id) WHERE retried IS NULL;'
+    end
+
+    yield
+
+    if Gitlab::Database.postgresql?
+      execute 'DROP INDEX CONCURRENTLY IF EXISTS index_for_ci_builds_retried_migration'
+    end
+  end
 end