Comment 6 for bug 1809174

So, 0.166s is very expensive in the sense that we can't do it every time we open the cache. We're literally optimizing every 10ms we can get there - apt-cache show would be twice as fast.

There are two more points where we could do those checks, though:

(1) in update - we can check if the lists we have are correct before deciding whether to download new ones
(2) in install - we can abort with an error before installing packages

The first one should essentially be free, and is probably the best way to fix the issue, as you don't see any upgrades, run update, and see them.