memorycache#get scans the whole cache for expired items on every fetch

[Matthew Gilliard]

Every time an item is fetched from the memory cache, the whole cache is scanned for expired items:

https://github.com/openstack/nova/blob/master/nova/openstack/common/memorycache.py#L63-L67

This is not the right place to expire items - a large cache can become slow. There should be a more sensible approach to the (difficult) problem of cache expiry.

[Joe Gordon (jogo)]

memorycache is synced in from oslo-incubator so the fix has to go there first.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/71559

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/96757

[OpenStack Infra (hudson-openstack)]

Change abandoned by Matthew Gilliard (<email address hidden>) on branch: master
Review: https://review.openstack.org/71559
Reason: indeed. See https://review.openstack.org/96757

[Ben Nemec (bnemec)]

Marking importance as low because there's some debate on the review as to whether this should even be fixed.

[OpenStack Infra (hudson-openstack)]

Change abandoned by Tom Cammann (<email address hidden>) on branch: master
Review: https://review.openstack.org/96757
Reason: Cache is to be left un-performant.

[Ben Nemec (bnemec)]

The in-memory cache isn't intended for production use anyway, so we don't want to spend a bunch of time optimizing it.