Try:
./etcdctl put foo bar
./etcdctl del foo
./etcdctl compact 3
restart etcd
./etcdctl get foo
mvcc: required revision has been compacted
The error is unexpected when range over the head revision.
Internally, we incorrectly set current revision smaller than the
compacted revision when we remove all keys around compacted revision.
This commit fixes the issue by recovering the current revision at least
to compacted revision.
The previous logic is wrong. When we have hisotry like Put(foo, bar, lease1),
and Put(foo, bar, lease2), we will end up with attaching foo to two leases 1 and
2. Similar things can happen for deattach by clearing the lease of a key.
Now we try to fix this by starting to attach leases at the end of the recovery.
We use a map to keep the last lease attachment state.
