akvo.cache.keys module

Cache key construction.

Kept free of imports from the rest of akvo so that it can be named from the settings files without pulling the application in while settings are still being assembled.

akvo.cache.keys.db_scoped_key(key, key_prefix, version)

Django cache key function that keeps parallel test workers out of each other’s cache.

manage.py test –parallel gives every worker its own clone of the database, each with its own sequences, so worker 1 and worker 3 both mint user id 5 and organisation id 7. They share a single memcached, and cache keys here are built from those ids - for instance user_filtered_projects:5:7:… in akvo.rsr.permissions, which decides whether a user may view a project. One worker could therefore read a value another worker derived from a different database, and the failure surfaces as a permission check that is wrong for no visible reason, in a test that passes when run on its own.

Including the database name makes each worker’s keyspace its own. The name is read per call rather than when settings load, which matters because workers are forked after that point and only then have their clone assigned.

Production is left alone: there is one database, ids are unique, and prefixing every key there would throw away the existing cache for no benefit.

One consequence worth knowing: AkvoMemcachedCache.list_keys recovers the logical key by splitting a raw key into three parts, so under a test database it would see the extra segment and return the wrong thing. Nothing calls it from the tests, and production keys keep their original shape, so this is noted rather than worked around.