Mahadev Konar wrote:
Hi Thomas,

More generally, is it a safe assumption to make that the ZooKeeper
service will maintain all its guarantees if a minority of servers lose
persistent state (due to bad disks, etc) and restart at some point in
the future?
Yes that is true.
Great - thanks Mahadev.

Not to drag this on more than necessary, please bear with me for one more example of 'amnesia' that comes to mind. I have a set of ZooKeeper servers A, B, C.
- C is currently not running, A is the leader, B is the follower.
- A proposes zxid1 to A and B, both acknowledge.
- A asks A to commit (which it persists), but before the same commit request reaches B, all servers go down (say a power failure). - Later, B and C come up (A is slow to reboot), but B has lost all state due to disk failure. - C becomes the new leader and perhaps continues with some more new transactions.

Likely I'm misunderstanding the protocol, but have I effectively lost zxid1 at this point? What would happen when A comes back up?


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