Tim Abbott bfaa698ea6 get_old_messages: Don't fetch messages from database unless we have to. ...

Previously, we were fetching Message.objects.select_related() from the
database, even if we actually ended up fetching the message dicts from
memcached and thus not actually using them.  Especially in the cached
case, this resulted in a lot of overhead where the Django ORM put
together Message objects with lots of data in them that were never
used.  This commit switches the model to only fetch the full message
objects from the database for those messages which are not found in
the memcached caches.

Here are the timings for get_old_messages before this patch was applied:

(cached)
127ms (db: 42ms/2q) /json/get_old_messages (starnine@mit.edu via website)
385ms (db: 105ms/1q) /json/get_old_messages (starnine@mit.edu via website)

(uncached)
315ms (mem: 6ms/41) (db: 90ms/22q) /json/get_old_messages (starnine@mit.edu via website)
507ms (db: 94ms/14q) /json/get_old_messages (starnine@mit.edu via website)

Here are the timings for get_old_messages after this patch was applied:

(cached)
 80ms (db: 9ms/2q) /json/get_old_messages (starnine@mit.edu via website)
133ms (db: 4ms/1q) /json/get_old_messages (starnine@mit.edu via website)

(uncached)
230ms (mem: 9ms/41) (db: 48ms/23q) /json/get_old_messages (starnine@mit.edu via website)
385ms (db: 55ms/15q) /json/get_old_messages (starnine@mit.edu via website)

(imported from commit c4748513392a906393314aa7cd41d98a69865411)

2013-05-02 15:32:23 -04:00

78 KiB

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