Comment 5 for bug 924283

> And update explicitly rebuilds the cache.

It would be really nice if we could get back the old behavior here - the cache gets only rebuilded if there are only real changes. But I have found an easier testcase to reproduce this issue:

root@ubuntu:~# time apt-get clean

real 0m0.025s
user 0m0.004s
sys 0m0.021s
root@ubuntu:~# time apt-get check firefox
Reading package lists... Done
Building dependency tree
Reading state information... Done

real 0m6.724s
user 0m3.423s
sys 0m0.148s
root@ubuntu:~# time apt-get check firefox
Reading package lists... Done
Building dependency tree
Reading state information... Done

real 0m0.447s
user 0m0.430s
sys 0m0.017s
root@ubuntu:~# time apt-get clean

real 0m0.018s
user 0m0.004s
sys 0m0.013s
root@ubuntu:~# time apt-get check firefox
Reading package lists... Done
Building dependency tree
Reading state information... Done

real 0m6.516s
user 0m3.371s
sys 0m0.161s

As this example shows "apt-get clean" causes the next command that reads from the package cache to rebuld it while there are even no explicit changes.