From 78b9f61dcab9bd571952b8c9e8052b643588c52b Mon Sep 17 00:00:00 2001
From: Tom Clegg <tom@curoverse.com>
Date: Mon, 8 Feb 2016 14:28:02 -0500
Subject: [PATCH] 8289: Strip redundant orders, even when provided explicitly
 by client.

---
 services/api/lib/load_param.rb                | 27 ++++++++++--
 .../test/functional/arvados/v1/query_test.rb  | 42 +++++++++++++++++++
 2 files changed, 65 insertions(+), 4 deletions(-)

diff --git a/services/api/lib/load_param.rb b/services/api/lib/load_param.rb
index c6c8ddfac4..d7b9bb7513 100644
--- a/services/api/lib/load_param.rb
+++ b/services/api/lib/load_param.rb
@@ -111,11 +111,30 @@ module LoadParam
     # (e.g., [] or ['owner_uuid desc']), fall back on the default
     # orders to ensure repeating the same request (possibly with
     # different limit/offset) will return records in the same order.
-    unless @orders.any? do |order|
-        otable, ocol = order.split(' ')[0].split('.')
-        otable == table_name and model_class.unique_columns.include?(ocol)
+    #
+    # Clean up the resulting list of orders such that no column
+    # uselessly appears twice (Postgres might not optimize this out
+    # for us) and no columns uselessly appear after a unique column
+    # (Postgres does not optimize this out for us; as of 9.2, "order
+    # by id, modified_at desc, uuid" is slow but "order by id" is
+    # fast).
+    orders_given_and_default = @orders + model_class.default_orders
+    order_cols_used = {}
+    @orders = []
+    orders_given_and_default.each do |order|
+      otablecol = order.split(' ')[0]
+
+      next if order_cols_used[otablecol]
+      order_cols_used[otablecol] = true
+
+      @orders << order
+
+      otable, ocol = otablecol.split('.')
+      if otable == table_name and model_class.unique_columns.include?(ocol)
+        # we already have a full ordering; subsequent entries would be
+        # superfluous
+        break
       end
-      @orders += model_class.default_orders
     end
 
     case params[:select]
diff --git a/services/api/test/functional/arvados/v1/query_test.rb b/services/api/test/functional/arvados/v1/query_test.rb
index 56db54c3a4..91fe077503 100644
--- a/services/api/test/functional/arvados/v1/query_test.rb
+++ b/services/api/test/functional/arvados/v1/query_test.rb
@@ -23,4 +23,46 @@ class Arvados::V1::QueryTest < ActionController::TestCase
     assert_equal('logs.event_type asc, logs.modified_at desc, logs.uuid',
                  assigns(:objects).order_values.join(', '))
   end
+
+  test 'skip fallback orders already given by client' do
+    @controller = Arvados::V1::LogsController.new
+    authorize_with :active
+    get :index, {
+      order: ['modified_at asc'],
+      controller: 'logs',
+    }
+    assert_response :success
+    assert_equal('logs.modified_at asc, logs.uuid',
+                 assigns(:objects).order_values.join(', '))
+  end
+
+  test 'eliminate superfluous orders' do
+    @controller = Arvados::V1::LogsController.new
+    authorize_with :active
+    get :index, {
+      order: ['logs.modified_at asc',
+              'modified_at desc',
+              'event_type desc',
+              'logs.event_type asc'],
+      controller: 'logs',
+    }
+    assert_response :success
+    assert_equal('logs.modified_at asc, logs.event_type desc, logs.uuid',
+                 assigns(:objects).order_values.join(', '))
+  end
+
+  test 'eliminate orders after the first unique column' do
+    @controller = Arvados::V1::LogsController.new
+    authorize_with :active
+    get :index, {
+      order: ['event_type asc',
+              'id asc',
+              'uuid asc',
+              'modified_at desc'],
+      controller: 'logs',
+    }
+    assert_response :success
+    assert_equal('logs.event_type asc, logs.id asc',
+                 assigns(:objects).order_values.join(', '))
+  end
 end
-- 
2.30.2