In issue 2551212 a new code path that cached the tracker invocation was added.
This was enabled via a feature flag for 2.2.0 because it arrived during the
beta window. Ralf's site has been running the cache code without issue AFAIK.

Today I made this new code path the default in changeset:   7819:0fe2b9f6e19f.
The feature flag can now be set to turn it off. See updating.txt for details.

The intent is to release 2.4.0 with the more performant code as the default.

If there are no reported issues after two years:

   delete the old code path
   retire the feature flag
   warn or exit if the feature flag is enabled so the admin can clean up
      Exiting would help flag tests that test the feature toggle.
   document the change in upgrading and add <del> markers to earlier
       instructions that talk about the feature
   remove the test for the toggle turning off the feature