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.
mahadev
>
> Thanks.
> Mahadev Konar wrote:
>> Hi Thomas,
>>
>> If a zookeeper server loses all state and their are enough servers in the
>> ensemble to continue a zookeeper service ( like 2 servers in the case of
>> ensemble of 3), then the server will get the latest snapshot from the leader
>> and continue.
>>
>>
>> The idea of zookeeper persisting its state on disk is just so that it does
>> not lose state. All the guarantees that zookeeper makes is based on the
>> understanding that we do not lose state of the data we store on the disk.
>>
>>
>> Their might be problems if we lose the state that we stored on the disk.
>> We might lose transactions that have been committed and the ensemble might
>> start with some snapshot in the past.
>>
>> You might want ot read through how zookeeper internals work. This will help
>> you understand on why the persistence guarantees are required.
>>
>> http://wiki.apache.org/hadoop-data/attachments/ZooKeeper(2f)ZooKeeperPresent
>> ations/attachments/zk-talk-upc.pdf
>>
>> mahadev
>>
>>
>>
>> On 12/16/08 9:45 AM, "Thomas Vinod Johnson" <Thomas.Johnson@Sun.COM> wrote:
>>
>>
>>> What is the expected behavior if a server in a ZooKeeper service
>>> restarts with all its prior state lost? Empirically, everything seems to
>>> work*. Is this something that one can count on, as part of ZooKeeper
>>> design, or are there known conditions under which this could cause
>>> problems, either liveness or violation of ZooKeeper guarantees?
>>>
>>> I'm really most interested in a situation where a single server loses
>>> state, but insights into issues when more than one server loses state
>>> and other interesting failure scenarios are appreciated.
>>>
>>> Thanks.
>>>
>>> * The restarted server appears to catch up to the latest snapshot (from
>>> the current leader?).
>>>
>>
>>
>
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