This is a long delayed followup to http://drupal.org/node/111127#comment-1494790
Reasons I'm posting this issue:
1. Despite converting lots of things to fields, caching at the node level rather than the field level gives a 10% performance improvement on a single node view with only the default profile and database caching. So the field cache does not 'do the same job' as an entity level cache as was suggested by Dries and bjaspan in that issue - it can't remove the cost of node_load() itself, the query building, the field_attach_load() calls etc.
2. I posted a proof-of-concept module at http://drupal.org/project/entitycache which implements node, taxonomy term and comment caching from contrib. This works, when hacked into the default profile, all but a couple of tests pass, and the entire .module is 14k - some of which is dead code for handling users which should probably be abandoned, some of which could probably be tidied up (pretty much all the NodeController / TaxonomyTermController overrides don't need to be there if we can call back to those classes directly), so potentially < 10k.
So, I'm proposing that we add this module to core, enabled in the default install profile. By having it as a separate module, we're able to maintain all the cache clearing code in one central place, so it doesn't have the messiness of putting node cache clears in taxonomy module, or taxonomy cache clears in image module or whatever. However we'll get real performance benefits in core rather than having to schlep off to contrib to get them.
We have real performance issues in Drupal 7, and this is one possible way to ameliorate those without changing any APIs (it adds a total of one hook). I'm not posting a patch here, since the code is in CVS, and this is more of an architecture/policy decision at this stage. Abusing status though to get it in the real issue queue.
