commit c2c108c7a404051dd51f317352ded9e0e5a5650d
author Patrick Hiesel <hiesel@google.com> Thu Jul 23 09:54:22 2020 +0200
committer Patrick Hiesel <hiesel@google.com> Tue Aug 11 14:51:49 2020 +0200
tree de28e03502a7824932815adaf0bce9c78d13c6f3
parent e2e28974a696e0e82dfde30b1a2eca82df742d2b

Persist ProjectCache

This commit splits the 'projects' cache into two pieces:
1) The 'projects' cache: This cache continues to work as
   it did before. It offers a by-name caching without the
   need to present or load the ObjectId of
   refs/meta/config.
2) The 'persisted_projects' cache: This cache is the
   persisted variant of 'projects'. It's used in the loader
   for 'projects' and - as all persisted caches - has the
   ObjectId in the key.

This new setup allows admins to persist the project cache -
if desired - to ease cold start times. This is an additional
performance improvement next to ProjectCacheWarmer. It might
at some point replace ProjectCacheWarmer. For now, the two
co-exist.

The split is done in this way to make sure we can still
access projects in the cache without loading a SHA1 for each
lookup as that would be prohibitively slow given the amount
of requests this cache serves.

Change-Id: I174076acd90ae815ac66e1e0f8a72db0701bf2d3