Distribution/DistroSeries overview wastes time querying languages and countries

[Jeroen T. Vermeulen]

We're seeing some timeouts for the Distribution and DistroSeries translation overview pages because they spend too much time looking up languages by code, and to a slightly lesser extent, countries and the languages that are spoken in them.

The language lookups in particular are pointless. We're querying Language by code about 10× as many times as there are languages listed in the overview. Some kind of caching and/or bulk-fetching seems in order.

OOPS-1492A1007, OOPS-1492A1146, OOPS-1492A1282, OOPS-1492A1362, OOPS-1492A1372
OOPS-1492A1456, OOPS-1492B1114, OOPS-1492B1170, OOPS-1492B1292, OOPS-1492B1533
OOPS-1492B1450, OOPS-1492D1484, OOPS-1492G1554, OOPS-1492G2077, OOPS-1492H60

[Jeroen T. Vermeulen (jtv)]

The cause seems to be that isPreferredLanguage indirectly looks up TranslationsMixin.translatable_languages, which uses preferred_or_request_languages from the Launchpad helpers, which in turn queries all of the languages set as the user's preferred languages or accepted by the http[s] request.

Since this is browser code, we can just make translatable_languages a @cachedproperty. It doesn't break any pagetests, and it looks like it'd knock >10 seconds off each of the timed-out requests.

[Jeroen T. Vermeulen (jtv)]

OOPS-1493A256, OOPS-1493A381, OOPS-1493B1491, OOPS-1493B1554, OOPS-1493B182
OOPS-1493A1351, OOPS-1493A1368, OOPS-1493A1573, OOPS-1493A626, OOPS-1493B1238
OOPS-1493C1002, OOPS-1493C1497, OOPS-1493C193, OOPS-1493C999, OOPS-1493O943
OOPS-1493G1262
OOPS-1493A623
OOPS-1493C1885, OOPS-1493D971
OOPS-1493A1094, OOPS-1493A276, OOPS-1493B891, OOPS-1493C1005, OOPS-1493C1415
OOPS-1493A1362, OOPS-1493A1408, OOPS-1493A1932, OOPS-1493A978, OOPS-1493E541

Actually, it *can* also happen with products or productseries:
OOPS-1493C1073, OOPS-1493F1677, OOPS-1493G2098, OOPS-1493H1260

[Jeroen T. Vermeulen (jtv)]

        OOPS-1493EA364, OOPS-1493EB531, OOPS-1493EB536
        OOPS-1493EA73, OOPS-1493EC309
OOPS-1493EB22
        OOPS-1493EA363, OOPS-1493EB280, OOPS-1493EC310
        OOPS-1493EA625, OOPS-1493EA66
        OOPS-1493EA398, OOPS-1493EB317

[Ursula Junque (ursinha)]

This bug was mentioned in stable r10246 <http://bazaar.launchpad.net/~launchpad-pqm/launchpad/stable/revision/10246>

[Jeroen T. Vermeulen (jtv)]

Yay! On edge this has taken all the problem pages out of the top-10 lists: timeouts, durations, and statement count.