Generation numbers and replacement objects

[Jakub Narebski <jnareb@gmail.com>]

[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).

-- 
Jakub Narebski