Extract data from cache in tornado_callbacks with cache_get_many

This reduces the number of memcached calls we make in our time-
slice-limited tornado event handler.

(imported from commit 8903ce4ac754ba82d57e04d1b0356be7533edee2)

zerver/lib/cache.py

@@ -233,6 +233,9 @@ def user_profile_by_email_cache_key(email):
 def user_profile_by_id_cache_key(user_profile_id):
     return "user_profile_by_id:%s" % (user_profile_id,)
 
+def cache_save_user_profile(user_profile):
+        cache_set(user_profile_by_id_cache_key(user_profile.id), user_profile, timeout=3600*24*7)
+
 # Called by models.py to flush the user_profile cache whenever we save
 # a user_profile object
 def update_user_profile_cache(sender, **kwargs):

zerver/tornado_callbacks.py

@@ -5,7 +5,9 @@ from zerver.models import Message, UserProfile, UserMessage, \
     Recipient, Stream, get_stream, get_user_profile_by_id
 
 from zerver.decorator import JsonableError
-from zerver.lib.cache_helpers import cache_get_message
+from zerver.lib.cache import cache_get_many, message_cache_key, \
+    user_profile_by_id_cache_key, cache_save_user_profile
+from zerver.lib.cache_helpers import cache_save_message
 from zerver.lib.queue import queue_json_publish
 from zerver.lib.event_queue import get_client_descriptors_for_user
 
@@ -249,11 +251,14 @@ def update_pointer(user_profile_id, new_pointer):
             client.add_event(event.copy())
 
 
-def receives_offline_notifications(user_profile_id):
-    user_profile = get_user_profile_by_id(user_profile_id)
+def receives_offline_notifications(user_profile):
     return (user_profile.enable_offline_email_notifications and
             not user_profile.is_bot)
 
+def receives_offline_notifications_by_id(user_profile_id):
+    user_profile = get_user_profile_by_id(user_profile_id)
+    return receives_offline_notifications(user_profile)
+
 def build_offline_notification_event(user_profile_id, message_id):
     return {"user_profile_id": user_profile_id,
             "message_id": message_id,
@@ -268,7 +273,7 @@ def missedmessage_hook(user_profile_id, queue, last_for_client):
     # If a user has gone offline but has unread messages
     # received in the idle time, send them a missed
     # message email
-    if not receives_offline_notifications(user_profile_id):
+    if not receives_offline_notifications_by_id(user_profile_id):
         return
 
     message_ids = []
@@ -283,14 +288,66 @@ def missedmessage_hook(user_profile_id, queue, last_for_client):
         event = build_offline_notification_event(user_profile_id, msg_id)
         queue_json_publish("missedmessage_emails", event, lambda event: None)
 
+def cache_load_message_data(message_id, users):
+    # Get everything that we'll need out of memcached in one fetch, to save round-trip times:
+    # * The message itself
+    # * Every recipient's UserProfile
+    user_profile_keys = [user_profile_by_id_cache_key(user_data['id']) for user_data in users]
+
+    cache_keys = [message_cache_key(message_id)]
+
+    cache_keys.extend(user_profile_keys)
+
+    # Single memcached fetch
+    result = cache_get_many(cache_keys)
+
+    cache_extractor = lambda result: result[0] if result is not None else None
+
+    message = cache_extractor(result.get(cache_keys[0], None))
+
+    user_profiles = dict((user_data['id'], cache_extractor(result.get(user_profile_by_id_cache_key(user_data['id']), None)))
+                            for user_data in users)
+
+    # Any data that was not found in memcached, we have to load from the database
+    # and save back. This should never happen---we take steps to keep recent messages,
+    # all user profile & presence objects in memcached.
+    if message is None:
+        if not settings.TEST_SUITE:
+            logging.warning("Tornado failed to load message from memcached when delivering!")
+
+        message = Message.objects.select_related().get(id=message_id)
+        cache_save_message(message)
+    for user_profile_id, user_profile in user_profiles.iteritems():
+        if user_profile:
+            continue
+        if not settings.TEST_SUITE:
+            logging.warning("Tornado failed to load user profile from memcached when delivering message!")
+
+        user_profile = UserProfile.objects.select_related().get(id=user_profile_id)
+        user_profiles[user_profile_id] = user_profile
+        cache_save_user_profile(user_profile)
+
+    return message, user_profiles
+
+def receiver_is_idle(user_profile):
+    # If a user has no message-receiving event queues, they've got no open zulip
+    # session so we notify them
+    all_client_descriptors = get_client_descriptors_for_user(user_profile.id)
+    message_event_queues = [client for client in all_client_descriptors if client.accepts_event_type('message')]
+    off_zulip = len(message_event_queues) == 0
+
+    return off_zulip
+
 def process_new_message(data):
-    message = cache_get_message(data['message'])
+    message, user_profiles = cache_load_message_data(data['message'],
+                                                     data['users'])
 
     message_dict_markdown = message.to_dict(True)
     message_dict_no_markdown = message.to_dict(False)
 
     for user_data in data['users']:
         user_profile_id = user_data['id']
+        user_profile = user_profiles[user_data['id']]
         flags = user_data.get('flags', [])
 
         user_receive_message(user_profile_id, message)
@@ -322,11 +379,11 @@ def process_new_message(data):
         received_pm = message.recipient.type in (Recipient.PERSONAL, Recipient.HUDDLE) and \
                         user_profile_id != message.sender.id
         mentioned = 'mentioned' in flags
-        all_client_descriptors = get_client_descriptors_for_user(user_profile_id)
-        message_event_queues = [client for client in all_client_descriptors if client.accepts_event_type('message')]
-        idle = len(message_event_queues) == 0
+
+        idle = receiver_is_idle(user_profile)
+
         if (received_pm or mentioned) and idle:
-            if receives_offline_notifications(user_profile_id):
+            if receives_offline_notifications(user_profile):
                 event = build_offline_notification_event(user_profile_id, message.id)
 
                 # We require RabbitMQ to do this, as we can't call the email handler