Merge pull request #8651 from edx/feanil/hotfix_commits_for_rc

Hotfix for performance of course structures

cms/envs/dev.py

@@ -115,7 +115,10 @@
         'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
         'LOCATION': 'edx_location_mem_cache',
     },
-
+    'course_structure_cache': {
+        'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
+        'LOCATION': 'edx_course_structure_mem_cache',
+    },
 }
 
 # Make the keyedcache startup warnings go away

cms/envs/test.py

@@ -166,7 +166,9 @@
         'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
         'LOCATION': 'edx_location_mem_cache',
     },
-
+    'course_structure_cache': {
+        'BACKEND': 'django.core.cache.backends.dummy.DummyCache',
+    },
 }
 
 # Add external_auth to Installed apps for testing

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

@@ -369,6 +369,19 @@ def __repr__(self):
             source_version="UNSET" if self.source_version is None else self.source_version,
         )  # pylint: disable=bad-continuation
 
+    def __eq__(self, edit_info):
+        """
+        Two EditInfo instances are equal iff their storable representations
+        are equal.
+        """
+        return self.to_storable() == edit_info.to_storable()
+
+    def __neq__(self, edit_info):
+        """
+        Two EditInfo instances are not equal if they're not equal.
+        """
+        return not self == edit_info
+
 
 class BlockData(object):
     """
@@ -426,6 +439,19 @@ def __repr__(self):
             classname=self.__class__.__name__,
         )  # pylint: disable=bad-continuation
 
+    def __eq__(self, block_data):
+        """
+        Two BlockData objects are equal iff all their attributes are equal.
+        """
+        attrs = ['fields', 'block_type', 'definition', 'defaults', 'edit_info']
+        return all(getattr(self, attr) == getattr(block_data, attr) for attr in attrs)
+
+    def __neq__(self, block_data):
+        """
+        Just define this as not self.__eq__(block_data)
+        """
+        return not self == block_data
+
 
 new_contract('BlockData', BlockData)
 

common/lib/xmodule/xmodule/modulestore/split_mongo/mongo_connection.py

@@ -2,7 +2,9 @@
 Segregation of pymongo functions from the data modeling mechanisms for split modulestore.
 """
 import datetime
+import cPickle as pickle
 import math
+import zlib
 import pymongo
 import pytz
 import re
@@ -11,6 +13,8 @@
 
 # Import this just to export it
 from pymongo.errors import DuplicateKeyError  # pylint: disable=unused-import
+from django.core.cache import get_cache, InvalidCacheBackendError
+import dogstats_wrapper as dog_stats_api
 
 from contracts import check, new_contract
 from mongodb_proxy import autoretry_read, MongoProxy
@@ -203,6 +207,50 @@ def structure_to_mongo(structure, course_context=None):
         return new_structure
 
 
+class CourseStructureCache(object):
+    """
+    Wrapper around django cache object to cache course structure objects.
+    The course structures are pickled and compressed when cached.
+
+    If the 'course_structure_cache' doesn't exist, then don't do anything for
+    for set and get.
+    """
+    def __init__(self):
+        self.no_cache_found = False
+        try:
+            self.cache = get_cache('course_structure_cache')
+        except InvalidCacheBackendError:
+            self.no_cache_found = True
+
+    def get(self, key):
+        """Pull the compressed, pickled struct data from cache and deserialize."""
+        if self.no_cache_found:
+            return None
+
+        compressed_pickled_data = self.cache.get(key)
+        if compressed_pickled_data is None:
+            return None
+        return pickle.loads(zlib.decompress(compressed_pickled_data))
+
+    def set(self, key, structure):
+        """Given a structure, will pickle, compress, and write to cache."""
+        if self.no_cache_found:
+            return None
+
+        pickled_data = pickle.dumps(structure, pickle.HIGHEST_PROTOCOL)
+        # 1 = Fastest (slightly larger results)
+        compressed_pickled_data = zlib.compress(pickled_data, 1)
+
+        # record compressed course structure sizes
+        dog_stats_api.histogram(
+            'compressed_course_structure.size',
+            len(compressed_pickled_data),
+            tags=[key]
+        )
+        # Stuctures are immutable, so we set a timeout of "never"
+        self.cache.set(key, compressed_pickled_data, None)
+
+
 class MongoConnection(object):
     """
     Segregation of pymongo functions from the data modeling mechanisms for split modulestore.
@@ -256,15 +304,23 @@ def heartbeat(self):
 
     def get_structure(self, key, course_context=None):
         """
-        Get the structure from the persistence mechanism whose id is the given key
+        Get the structure from the persistence mechanism whose id is the given key.
+
+        This method will use a cached version of the structure if it is availble.
         """
         with TIMER.timer("get_structure", course_context) as tagger_get_structure:
-            with TIMER.timer("get_structure.find_one", course_context) as tagger_find_one:
-                doc = self.structures.find_one({'_id': key})
-                tagger_find_one.measure("blocks", len(doc['blocks']))
-            tagger_get_structure.measure("blocks", len(doc['blocks']))
-
-            return structure_from_mongo(doc, course_context)
+            cache = CourseStructureCache()
+
+            structure = cache.get(key)
+            tagger_get_structure.tag(from_cache='true' if structure else 'false')
+            if not structure:
+                with TIMER.timer("get_structure.find_one", course_context) as tagger_find_one:
+                    doc = self.structures.find_one({'_id': key})
+                    tagger_find_one.measure("blocks", len(doc['blocks']))
+                    structure = structure_from_mongo(doc, course_context)
+                cache.set(key, structure)
+
+            return structure
 
     @autoretry_read()
     def find_structures_by_id(self, ids, course_context=None):

common/lib/xmodule/xmodule/modulestore/tests/test_split_modulestore.py

@@ -12,6 +12,7 @@
 
 from contracts import contract
 from nose.plugins.attrib import attr
+from django.core.cache import get_cache, InvalidCacheBackendError
 
 from openedx.core.lib import tempdir
 from xblock.fields import Reference, ReferenceList, ReferenceValueDict
@@ -29,6 +30,7 @@
 from xmodule.modulestore.split_mongo.split import SplitMongoModuleStore
 from xmodule.modulestore.tests.test_modulestore import check_has_course_method
 from xmodule.modulestore.split_mongo import BlockKey
+from xmodule.modulestore.tests.factories import check_mongo_calls
 from xmodule.modulestore.tests.mongo_connection import MONGO_PORT_NUM, MONGO_HOST
 from xmodule.modulestore.tests.utils import mock_tab_from_json
 from xmodule.modulestore.edit_info import EditInfoMixin
@@ -771,6 +773,79 @@ def test_course_successors(self, _from_json):
         self.assertEqual(result.children[0].children[0].locator.version_guid, versions[0])
 
 
+class TestCourseStructureCache(SplitModuleTest):
+    """Tests for the CourseStructureCache"""
+
+    def setUp(self):
+        # use the default cache, since the `course_structure_cache`
+        # is a dummy cache during testing
+        self.cache = get_cache('default')
+
+        # make sure we clear the cache before every test...
+        self.cache.clear()
+        # ... and after
+        self.addCleanup(self.cache.clear)
+
+        # make a new course:
+        self.user = random.getrandbits(32)
+        self.new_course = modulestore().create_course(
+            'org', 'course', 'test_run', self.user, BRANCH_NAME_DRAFT,
+        )
+
+        super(TestCourseStructureCache, self).setUp()
+
+    @patch('xmodule.modulestore.split_mongo.mongo_connection.get_cache')
+    def test_course_structure_cache(self, mock_get_cache):
+        # force get_cache to return the default cache so we can test
+        # its caching behavior
+        mock_get_cache.return_value = self.cache
+
+        with check_mongo_calls(1):
+            not_cached_structure = self._get_structure(self.new_course)
+
+        # when cache is warmed, we should have one fewer mongo call
+        with check_mongo_calls(0):
+            cached_structure = self._get_structure(self.new_course)
+
+        # now make sure that you get the same structure
+        self.assertEqual(cached_structure, not_cached_structure)
+
+    @patch('xmodule.modulestore.split_mongo.mongo_connection.get_cache')
+    def test_course_structure_cache_no_cache_configured(self, mock_get_cache):
+        mock_get_cache.side_effect = InvalidCacheBackendError
+
+        with check_mongo_calls(1):
+            not_cached_structure = self._get_structure(self.new_course)
+
+        # if the cache isn't configured, we expect to have to make
+        # another mongo call here if we want the same course structure
+        with check_mongo_calls(1):
+            cached_structure = self._get_structure(self.new_course)
+
+        # now make sure that you get the same structure
+        self.assertEqual(cached_structure, not_cached_structure)
+
+    def test_dummy_cache(self):
+        with check_mongo_calls(1):
+            not_cached_structure = self._get_structure(self.new_course)
+
+        # Since the test is using the dummy cache, it's not actually caching
+        # anything
+        with check_mongo_calls(1):
+            cached_structure = self._get_structure(self.new_course)
+
+        # now make sure that you get the same structure
+        self.assertEqual(cached_structure, not_cached_structure)
+
+    def _get_structure(self, course):
+        """
+        Helper function to get a structure from a course.
+        """
+        return modulestore().db_connection.get_structure(
+            course.location.as_object_id(course.location.version_guid)
+        )
+
+
 class SplitModuleItemTests(SplitModuleTest):
     '''
     Item read tests including inheritance

lms/envs/dev.py

@@ -94,6 +94,10 @@
         'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
         'LOCATION': 'edx_location_mem_cache',
     },
+    'course_structure_cache': {
+        'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
+        'LOCATION': 'edx_course_structure_mem_cache',
+    },
 }
 
 

lms/envs/test.py

@@ -207,7 +207,9 @@
         'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
         'LOCATION': 'edx_location_mem_cache',
     },
-
+    'course_structure_cache': {
+        'BACKEND': 'django.core.cache.backends.dummy.DummyCache',
+    },
 }
 
 # Dummy secret key for dev