Bug 1183082 - Fix attachment feeds.

[jezdez]

No description provided.

[darkwing]

@jezdez "attachment" ! :)

[groovecoder]

Would select_related be more efficient here, since creator and attachment are both ForeignKey relations? select_related would get them in the same query with a SQL join, rather than prefetch_related doing separate lookups for each and joining in Python?

[jezdez]

Yeah, select_related would do this in one query, but since we're running on a MySQL cluster with query cache on it would essentially invalidate the query cache if any of the inner join tables is changed, e.g. if a new user is added or even just updated.

So assuming a case in which a new user signs up, using prefetch_related here would only trigger the invalidation of the query cache for the creator prefetch query. While the other two for the attachment revision and the attachment would come straight from memory. All in all this is a micro optimization that given the number of queries we do against MySQL may not matter, but it's nicer to use the query cache as much as possible and live with the slight overhead on the Python side.

[groovecoder]

Makes sense. r+

[groovecoder]

r+ with comments