Decrease the number of queries needed for LMS courseware

This cuts the number of queries in 6.002 courseware loads from ~650 to
~5-40. Still to do: cache CustomTag templates so that we only load them
once per request.

cms/djangoapps/contentstore/views.py

@@ -475,7 +475,7 @@ def preview_module_system(request, preview_id, descriptor):
     )
 
 
-def get_preview_module(request, preview_id, location):
+def get_preview_module(request, preview_id, descriptor):
     """
     Returns a preview XModule at the specified location. The preview_data is chosen arbitrarily
     from the set of preview data for the descriptor specified by Location
@@ -484,7 +484,6 @@ def get_preview_module(request, preview_id, location):
     preview_id (str): An identifier specifying which preview this module is used for
     location: A Location
     """
-    descriptor = modulestore().get_item(location)
     instance_state, shared_state = descriptor.get_sample_state()[0]
     return load_preview_module(request, preview_id, descriptor, instance_state, shared_state)
 

common/lib/xmodule/xmodule/abtest_module.py

@@ -52,9 +52,10 @@ class ABTestModule(XModule):
     def get_shared_state(self):
         return json.dumps({'group': self.group})
     
-    def get_children_locations(self):
-        return self.definition['data']['group_content'][self.group]
-        
+    def get_child_descriptors(self):
+        active_locations = set(self.definition['data']['group_content'][self.group])
+        return [desc for desc in self.descriptor.get_children() if desc.location.url() in active_locations]
+
     def displayable_items(self):
         # Most modules return "self" as the displayable_item. We never display ourself
         # (which is why we don't implement get_html). We only display our children.

common/lib/xmodule/xmodule/modulestore/__init__.py

@@ -265,7 +265,7 @@ class ModuleStore(object):
         """
         raise NotImplementedError
 
-    def get_instance(self, course_id, location):
+    def get_instance(self, course_id, location, depth=0):
         """
         Get an instance of this location, with policy for course_id applied.
         TODO (vshnayder): this may want to live outside the modulestore eventually

common/lib/xmodule/xmodule/modulestore/mongo.py

@@ -82,17 +82,26 @@ def location_to_query(location, wildcard=True):
     If `wildcard` is True, then a None in a location is treated as a wildcard
     query. Otherwise, it is searched for literally
     """
-    query = SON()
-    # Location dict is ordered by specificity, and SON
-    # will preserve that order for queries
-    for key, val in Location(location).dict().iteritems():
-        if wildcard and val is None:
-            continue
-        query['_id.{key}'.format(key=key)] = val
+    query = namedtuple_to_son(Location(location), prefix='_id.')
+
+    if wildcard:
+        for key, value in query.items():
+            if value is None:
+                del query[key]
 
     return query
 
 
+def namedtuple_to_son(namedtuple, prefix=''):
+    """
+    Converts a namedtuple into a SON object with the same key order
+    """
+    son = SON()
+    for idx, field_name in enumerate(namedtuple._fields):
+        son[prefix + field_name] = namedtuple[idx]
+    return son
+
+
 class MongoModuleStore(ModuleStoreBase):
     """
     A Mongodb backed ModuleStore
@@ -149,6 +158,7 @@ class MongoModuleStore(ModuleStoreBase):
         If depth is None, will load all the children.
         This will make a number of queries that is linear in the depth.
         """
+
         data = {}
         to_process = list(items)
         while to_process and depth is None or depth >= 0:
@@ -162,8 +172,10 @@ class MongoModuleStore(ModuleStoreBase):
             # http://www.mongodb.org/display/DOCS/Advanced+Queries#AdvancedQueries-%24or
             # for or-query syntax
             if children:
-                to_process = list(self.collection.find(
-                    {'_id': {'$in': [Location(child).dict() for child in children]}}))
+                query = {
+                    '_id': {'$in': [namedtuple_to_son(Location(child)) for child in children]}
+                }
+                to_process = self.collection.find(query)
             else:
                 to_process = []
             # If depth is None, then we just recurse until we hit all the descendents
@@ -255,12 +267,17 @@ class MongoModuleStore(ModuleStoreBase):
         item = self._find_one(location)
         return self._load_items([item], depth)[0]
 
-    def get_instance(self, course_id, location):
+    def get_instance(self, course_id, location, depth=0):
         """
         TODO (vshnayder): implement policy tracking in mongo.
         For now, just delegate to get_item and ignore policy.
+
+        depth (int): An argument that some module stores may use to prefetch
+            descendents of the queried modules for more efficient results later
+            in the request. The depth is counted in the number of
+            calls to get_children() to cache. None indicates to cache all descendents.
         """
-        return self.get_item(location)
+        return self.get_item(location, depth=depth)
 
     def get_items(self, location, course_id=None, depth=0):
         items = self.collection.find(

common/lib/xmodule/xmodule/template_module.py

@@ -61,7 +61,7 @@ class CustomTagDescriptor(RawDescriptor):
         # cdodge: look up the template as a module
         template_loc = self.location._replace(category='custom_tag_template', name=template_name)
 
-        template_module = modulestore().get_instance(system.course_id, template_loc)
+        template_module = self.system.load_item(template_loc)
         template_module_data = template_module.definition['data']
         template = Template(template_module_data)
         return template.render(**params)

common/lib/xmodule/xmodule/x_module.py

@@ -241,17 +241,17 @@ class XModule(HTMLSnippet):
         Return module instances for all the children of this module.
         '''
         if self._loaded_children is None:
-            child_locations = self.get_children_locations()
-            children = [self.system.get_module(loc) for loc in child_locations]
+            child_descriptors = self.get_child_descriptors()
+            children = [self.system.get_module(descriptor) for descriptor in child_descriptors]
             # get_module returns None if the current user doesn't have access
             # to the location.
             self._loaded_children = [c for c in children if c is not None]
 
         return self._loaded_children
 
-    def get_children_locations(self):
+    def get_child_descriptors(self):
         '''
-        Returns the locations of each of child modules.
+        Returns the descriptors of the child modules
 
         Overriding this changes the behavior of get_children and
         anything that uses get_children, such as get_display_items.
@@ -262,7 +262,16 @@ class XModule(HTMLSnippet):
         These children will be the same children returned by the
         descriptor unless descriptor.has_dynamic_children() is true.
         '''
-        return self.definition.get('children', [])
+        return self.descriptor.get_children()
+
+    def get_child_by(self, selector):
+        """
+        Return a child XModuleDescriptor with the specified url_name, if it exists, and None otherwise.
+        """
+        for child in self.get_children():
+            if selector(child):
+                return child
+        return None
 
     def get_display_items(self):
         '''
@@ -577,13 +586,13 @@ class XModuleDescriptor(Plugin, HTMLSnippet, ResourceTemplates):
 
         return self._child_instances
 
-    def get_child_by_url_name(self, url_name):
+    def get_child_by(self, selector):
         """
         Return a child XModuleDescriptor with the specified url_name, if it exists, and None otherwise.
         """
-        for c in self.get_children():
-            if c.url_name == url_name:
-                return c
+        for child in self.get_children():
+            if selector(child):
+                return child
         return None
 
     def xmodule_constructor(self, system):
@@ -847,7 +856,7 @@ class ModuleSystem(object):
                          TODO: Not used, and has inconsistent args in different
                          files.  Update or remove.
 
-        get_module - function that takes (location) and returns a corresponding
+        get_module - function that takes a descriptor and returns a corresponding
                          module instance object.  If the current user does not have
                          access to that location, returns None.
 

lms/djangoapps/courseware/courses.py

@@ -42,28 +42,31 @@ def get_request_for_thread():
         del frame
 
 
-def get_course_by_id(course_id):
+def get_course_by_id(course_id, depth=0):
     """
     Given a course id, return the corresponding course descriptor.
 
     If course_id is not valid, raises a 404.
+    depth: The number of levels of children for the modulestore to cache. None means infinite depth
     """
     try:
         course_loc = CourseDescriptor.id_to_location(course_id)
-        return modulestore().get_instance(course_id, course_loc)
+        return modulestore().get_instance(course_id, course_loc, depth=depth)
     except (KeyError, ItemNotFoundError):
         raise Http404("Course not found.")
 
 
-def get_course_with_access(user, course_id, action):
+def get_course_with_access(user, course_id, action, depth=0):
     """
     Given a course_id, look up the corresponding course descriptor,
     check that the user has the access to perform the specified action
     on the course, and return the descriptor.
 
     Raises a 404 if the course_id is invalid, or the user doesn't have access.
+
+    depth: The number of levels of children for the modulestore to cache. None means infinite depth
     """
-    course = get_course_by_id(course_id)
+    course = get_course_by_id(course_id, depth=depth)
     if not has_access(user, course, action):
         # Deliberately return a non-specific error message to avoid
         # leaking info about access control settings

lms/djangoapps/courseware/grades.py

@@ -291,7 +291,7 @@ def progress_summary(student, request, course, student_module_cache):
             graded = section_module.metadata.get('graded', False)
             scores = []
             
-            module_creator = lambda descriptor : section_module.system.get_module(descriptor.location)
+            module_creator = section_module.system.get_module
             
             for module_descriptor in yield_dynamic_descriptor_descendents(section_module.descriptor, module_creator):
                 

lms/djangoapps/courseware/module_render.py

@@ -82,7 +82,8 @@ def toc_for_course(user, request, course, active_chapter, active_section):
 
     student_module_cache = StudentModuleCache.cache_for_descriptor_descendents(
         course.id, user, course, depth=2)
-    course_module = get_module(user, request, course.location, student_module_cache, course.id)
+    course_module = get_module_for_descriptor(user, request, course,
+                                              student_module_cache, course.id)
     if course_module is None:
         return None
 
@@ -115,7 +116,9 @@ def toc_for_course(user, request, course, active_chapter, active_section):
     return chapters
 
 
-def get_module(user, request, location, student_module_cache, course_id, position=None, not_found_ok = False, wrap_xmodule_display = True):
+def get_module(user, request, location, student_module_cache, course_id,
+               position=None, not_found_ok=False, wrap_xmodule_display=True,
+               depth=0):
     """
     Get an instance of the xmodule class identified by location,
     setting the state based on an existing StudentModule, or creating one if none
@@ -130,13 +133,28 @@ def get_module(user, request, location, student_module_cache, course_id, positio
       - course_id             : the course_id in the context of which to load module
       - position              : extra information from URL for user-specified
                                 position within module
+      - depth                 : number of levels of descendents to cache when loading this module.
+                                None means cache all descendents
 
     Returns: xmodule instance, or None if the user does not have access to the
     module.  If there's an error, will try to return an instance of ErrorModule
     if possible.  If not possible, return None.
     """
+    location = Location(location)
+    descriptor = modulestore().get_instance(course_id, location, depth=depth)
+    return get_module_for_descriptor(user, request, descriptor, student_module_cache, course_id,
+                                     position=position, not_found_ok=not_found_ok,
+                                     wrap_xmodule_display=wrap_xmodule_display)
+
+
+def get_module_for_descriptor(user, request, descriptor, student_module_cache, course_id,
+                              position=None, not_found_ok=False, wrap_xmodule_display=True):
+    """
+    Actually implement get_module. See docstring there for details.
+    """
     try:
-        return _get_module(user, request, location, student_module_cache, course_id, position, wrap_xmodule_display)
+        return _get_module(user, request, descriptor, student_module_cache, course_id,
+                           position=position, wrap_xmodule_display=wrap_xmodule_display)
     except ItemNotFoundError:
         if not not_found_ok:
             log.exception("Error in get_module")
@@ -146,12 +164,12 @@ def get_module(user, request, location, student_module_cache, course_id, positio
         log.exception("Error in get_module")
         return None
 
-def _get_module(user, request, location, student_module_cache, course_id, position=None, wrap_xmodule_display = True):
+
+def _get_module(user, request, descriptor, student_module_cache, course_id,
+                position=None, wrap_xmodule_display=True):
     """
     Actually implement get_module.  See docstring there for details.
     """
-    location = Location(location)
-    descriptor = modulestore().get_instance(course_id, location)
 
     # Short circuit--if the user shouldn't have access, bail without doing any work
     if not has_access(user, descriptor, 'load', course_id):
@@ -206,12 +224,12 @@ def _get_module(user, request, location, student_module_cache, course_id, positi
               'waittime': settings.XQUEUE_WAITTIME_BETWEEN_REQUESTS
              }
 
-    def inner_get_module(location):
+    def inner_get_module(descriptor):
         """
         Delegate to get_module.  It does an access check, so may return None
         """
-        return get_module(user, request, location,
-                                       student_module_cache, course_id, position)
+        return get_module_for_descriptor(user, request, descriptor,
+                                         student_module_cache, course_id, position)
 
     # TODO (cpennington): When modules are shared between courses, the static
     # prefix is going to have to be specific to the module, not the directory
@@ -246,7 +264,7 @@ def _get_module(user, request, location, student_module_cache, course_id, positi
 
         # make an ErrorDescriptor -- assuming that the descriptor's system is ok
         import_system = descriptor.system
-        if has_access(user, location, 'staff', course_id):
+        if has_access(user, descriptor.location, 'staff', course_id):
             err_descriptor = ErrorDescriptor.from_xml(str(descriptor), import_system,
                                                       error_msg=exc_info_to_str(sys.exc_info()))
         else:

lms/djangoapps/courseware/views.py

@@ -20,7 +20,7 @@ from courseware.access import has_access
 from courseware.courses import (get_courses, get_course_with_access, get_courses_by_university)
 import courseware.tabs as tabs
 from courseware.models import StudentModuleCache
-from module_render import toc_for_course, get_module, get_instance_module
+from module_render import toc_for_course, get_module, get_instance_module, get_module_for_descriptor
 
 from django_comment_client.utils import get_discussion_title
 
@@ -180,7 +180,7 @@ def index(request, course_id, chapter=None, section=None,
 
      - HTTPresponse
     """
-    course = get_course_with_access(request.user, course_id, 'load')
+    course = get_course_with_access(request.user, course_id, 'load', depth=2)
     staff_access = has_access(request.user, course, 'staff')
     registered = registered_for_course(course, request.user)
     if not registered:
@@ -195,7 +195,8 @@ def index(request, course_id, chapter=None, section=None,
         # Has this student been in this course before?
         first_time = student_module_cache.lookup(course_id, 'course', course.location.url()) is None
 
-        course_module = get_module(request.user, request, course.location, student_module_cache, course.id)
+        # Load the module for the course
+        course_module = get_module_for_descriptor(request.user, request, course, student_module_cache, course.id)
         if course_module is None:
             log.warning('If you see this, something went wrong: if we got this'
                         ' far, should have gotten a course module for this user')
@@ -215,30 +216,28 @@ def index(request, course_id, chapter=None, section=None,
             'xqa_server': settings.MITX_FEATURES.get('USE_XQA_SERVER','http://xqa:server@content-qa.mitx.mit.edu/xqa')
             }
 
-        chapter_descriptor = course.get_child_by_url_name(chapter)
+        chapter_descriptor = course.get_child_by(lambda m: m.url_name == chapter)
         if chapter_descriptor is not None:
             instance_module = get_instance_module(course_id, request.user, course_module, student_module_cache)
             save_child_position(course_module, chapter, instance_module)
         else:
             raise Http404
 
-        chapter_module = get_module(request.user, request, chapter_descriptor.location,
-                                    student_module_cache, course_id)
+        chapter_module = course_module.get_child_by(lambda m: m.url_name == chapter)
         if chapter_module is None:
             # User may be trying to access a chapter that isn't live yet
             raise Http404
 
         if section is not None:
-            section_descriptor = chapter_descriptor.get_child_by_url_name(section)
+            section_descriptor = chapter_descriptor.get_child_by(lambda m: m.url_name == section)
             if section_descriptor is None:
                 # Specifically asked-for section doesn't exist
                 raise Http404
 
-            section_student_module_cache = StudentModuleCache.cache_for_descriptor_descendents(
-                course_id, request.user, section_descriptor)
-            section_module = get_module(request.user, request,
-                                section_descriptor.location,
-                                section_student_module_cache, course_id, position)
+            # Load all descendents of the section, because we're going to display it's
+            # html, which in general will need all of its children
+            section_module = get_module(request.user, request, section_descriptor.location,
+                                        student_module_cache, course.id, depth=None)
             if section_module is None:
                 # User may be trying to be clever and access something
                 # they don't have access to.