Generation numbers and replacement objects

[Sorry for sending this email like this, but I forgot where
 I wanted to attach it to threads]

Peff, as Junio said somewhere else either in this thread, or the one started by Linus, we would want generation numbers both without taking into account replacement objects (e.g. for object traversal during push / fetch), and with taking it into account (e.g. when showing log or blame for end user).

So we would need two generation number caches: one with and one without replaces. Nb. generation header stored in commit object can give only the one without replaces, i.e. speed up object enumeration (what happened to caching GSoC project code?) but not git-log.

Also if replacement object has the same generation as the commit it replaces, and I think also if it has lower generation number, current generation numbers would still work (ne need to invalidate cache).