CSC/ECE 517 Spring 2015/oss E1510 FLP

Expertiza - Fix Instructor Login Performance Issue

Expertiza is a web application where students can submit and peer-review learning objects (articles, code, web sites, etc). It is used in select courses at NC State and by professors at several other colleges and universities.<ref>Expertiza on GitHub</ref>

Project Description

Currently when an Instructor logs into Expertiza,there a lot of select* from assignments queries being fired on database which would have an adverse effect on performance. We analyzed the source of this issue and made some changes, which reduced the number of select queries executed. The performance is high improved. The mission involved is tracing the source of the issue and modify the code to fix the issue.

Performance issue before modification

  Assignment Load (0.1ms)  SELECT  `assignments`.* FROM `assignments`  WHERE `assignments`.`id` = 1 LIMIT 1
  CACHE (0.0ms)  SELECT  `assignments`.* FROM `assignments`  WHERE `assignments`.`id` = 1 LIMIT 1  [["id", 1]]
  CACHE (0.0ms)  SELECT  `assignments`.* FROM `assignments`  WHERE `assignments`.`id` = 1 LIMIT 1  [["id", 1]]
  CACHE (0.0ms)  SELECT  `assignments`.* FROM `assignments`  WHERE `assignments`.`id` = 1 LIMIT 1  [["id", 1]]
  CACHE (0.2ms)  SELECT  `assignments`.* FROM `assignments`  WHERE `assignments`.`id` = 1 LIMIT 1  [["id", 1]]
  CACHE (0.1ms)  SELECT  `assignments`.* FROM `assignments`  WHERE `assignments`.`id` = 1 LIMIT 1  [["id", 1]]
  CACHE (0.1ms)  SELECT  `assignments`.* FROM `assignments`  WHERE `assignments`.`id` = 1 LIMIT 1  [["id", 1]]
  Rendered tree_display/_row_header.html.erb (17.4ms)

  CACHE (0.0ms)  SELECT  `assignments`.* FROM `assignments`  WHERE `assignments`.`id` = 1 LIMIT 1  [["id", 1]]
  Assignment Load (0.2ms)  SELECT  `assignments`.* FROM `assignments`  WHERE `assignments`.`id` = 1 LIMIT 1
  CACHE (0.0ms)  SELECT  `assignments`.* FROM `assignments`  WHERE `assignments`.`id` = 1 LIMIT 1  [["id", 1]]
  Rendered tree_display/actions/_shared_actions.html.erb (2.6ms)

  CACHE (0.0ms)  SELECT  `assignments`.* FROM `assignments`  WHERE `assignments`.`id` = 1 LIMIT 1  [["id", 1]]
  SignUpTopic Load (0.1ms)  SELECT  `sign_up_topics`.* FROM `sign_up_topics`  WHERE (assignment_id = 1)  ORDER BY `sign_up_topics`.`id` ASC LIMIT 1
  CACHE (0.0ms)  SELECT  `assignments`.* FROM `assignments`  WHERE `assignments`.`id` = 1 LIMIT 1  [["id", 1]]
  Rendered tree_display/actions/_assignments_actions.html.erb (8.8ms)

we can see that there are 7 assignment queries after load _row_header.html.erb, 3 assignment queries after load _shared_actions.html.erb, 3 assignment queries after load _assignments_actions. All these have an adverse effect on the performance.

Locate bug

Analyze code

_assignment_actions.html.erb

In file _assignment_actions.html.erb, we can find in 3 places use Assignment.find(node.node_object_id), which is actually a database query request.

1  <% owner_id = Object.const_get('Assignment').find(node.node_object_id).instructor_id %>
...
11 <% @assignment = Assignment.find(node.node_object_id) %>
...
52 <% if Assignment.find(node.node_object_id).course_id %>
...

_row_header.html.erb and assignment_node.rb

In _row_header.html.erb:

26  <% if parent_node.get_name == 'Courses'&& session[:user].role_id == 6 %>
27  <%else%>
28    <%= parent_node.get_name %>
29    <% if parent_node.get_directory != nil%>
30      <BR/><I>Directory:</I> <%= parent_node.get_directory %>
31    <% end %>
32    <% if parent_node.get_creation_date != nil %>
33      <BR/><I>Creation Date:</I> <%= parent_node.get_creation_date %>
34    <% end %>
35    <% if parent_node.get_modified_date != nil %>
36      <BR/><I>Updated Date:</I> <%= parent_node.get_modified_date %>
37    <% end %>
38  <%end%>

we can see in this view, parent_node is a AssignmentNode object, it execute:

• parent_node.get_name method
• parent_node.get_directory method
• parent_node.get_creation_date method
• parent_node.get_modified_date method

However, in assignment_node.rb:

6  class AssignmentNode < Node
   ...   
58   # Gets the name from the associated object
59   def get_name
60     Assignment.find(self.node_object_id).name
61   end
62 
63   # Gets the directory_path from the associated object
64   def get_directory
65     Assignment.find(self.node_object_id).directory_path
66   end
67 
68   # Gets the created_at from the associated object
69   def get_creation_date
70     Assignment.find(self.node_object_id).created_at
71   end
72
73   # Gets the updated_at from the associated object
74   def get_modified_date
75     Assignment.find(self.node_object_id).updated_at
76   end
   ...
82 end

We find all these method called Assignment.find(self.node_object_id) method, which is actually a database query request.

Modifications

_assignment_actions.html.erb

+ <% @assignment = Assignment.find(node.node_object_id) %>
+ <% owner_id = @assignment.instructor_id %>
- <% owner_id = Object.const_get('Assignment').find(node.node_object_id).instructor_id %>
...
-
...
+ <% if @assignment.course_id %>
-
...

References

<references/>