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From Martin Serrano <mar...@attivio.com>
Subject Re: FYI - Apache ZooKeeper Backup, a Treatise
Date Sat, 18 Jun 2016 02:25:15 GMT
Why are you seeking to undo it?

On 06/17/2016 09:34 PM, Andrew Purtell wrote:
> HBase stores replication peering configuration in ZK. We're working on
> undoing that, but for now that information exists nowhere else.
> On Thu, Jun 16, 2016 at 2:47 PM, Ismael Juma <ismael@juma.me.uk> wrote:
>> Hi Jordan,
>> Kafka stores ACLs as well as client and topic configs in ZooKeeper so that
>> lends credence to your argument, I think.
>> Ismael
>> On Thu, Jun 16, 2016 at 11:41 PM, Jordan Zimmerman <
>> jordan@jordanzimmerman.com> wrote:
>>> Contrary to recommendations everywhere, my experience is that almost
>>> everyone is storing source of truth data in ZooKeeper. It’s just too
>>> tempting. You have a distributed file system just sitting there and it’s
>>> too easy to use. You get a lot of great features like watches, etc.
>> People
>>> are using it to store configuration data, sequence numbers, etc. They are
>>> storing these things without a good means of reproducing them in case of
>> a
>>> catastrophic outage. Further, I’ve heard of several orgs who just back up
>>> the transaction logs and think they can restore them for DR. Anyway,
>> that’s
>>> the genesis of my blog post.
>>> -Jordan
>>>> On Jun 16, 2016, at 2:39 PM, Chris Nauroth <cnauroth@hortonworks.com>
>>> wrote:
>>>> Yes, thank you to Jordan for the article!
>>>> Like Flavio, I personally have never come across the requirement for
>>>> ZooKeeper backups.  I've generally followed the pattern that data
>> stored
>>>> in ZooKeeper is truly transient, and applications are built either to
>>>> tolerate loss of that data or reconstruct it from first principles if
>> it
>>>> goes missing.  Adding observers in a second data center would give a
>>>> rudimentary approximation of off-site backup in the case of a data
>> center
>>>> disaster, with the usual caveats around propagation delays.
>>>> Jordan, I'd be curious if you can share more specific details about the
>>>> kind of data that you have that necessitates a backup/restore.  (If
>>> you're
>>>> not at liberty to share this, then I can understand that.)  It might
>>>> inform if we have a motivating use case for backup/restore features
>>> within
>>>> ZooKeeper, such as some of the transaction log filtering that the
>> article
>>>> mentions.
>>>> --Chris Nauroth
>>>> On 6/16/16, 1:03 AM, "Flavio Junqueira" <fpj@apache.org> wrote:
>>>>> Great write-up, Jordan, thanks!
>>>>> Whether to backup zk data or not is possibly an open topic for this
>>>>> community, even though we have discussed it at times. My sense has
>> been
>>>>> that precisely because of the issues you mention in your post, it is
>>>>> typically best to have a way to recreate its data upon a disaster
>> rather
>>>>> than backup the data. I think there could be three general scenarios
>> in
>>>>> which folks would prefer to backup data, but you correct me if these
>>>>> aren't accurate:
>>>>> - The data in zk isn't elsewhere, so it can't be recreated: zk isn't
>>>>> regular database, so I'd think it is best not to store data and focus
>> on
>>>>> cluster data or metadata.
>>>>> - There is a just a lot of data and I'd rather have a shorter time to
>>>>> recover: zk in general shouldn't have that much data in db, but let's
>> go
>>>>> with the assumption that for the requirements of the application it
>> is a
>>>>> lot. For such a case, it probably depends on whether your application
>>> can
>>>>> efficiently and effectively recover from a backup. Basically, as
>> pointed
>>>>> out in the post, the data could be inconsistent and cause trouble if
>> you
>>>>> don't think about the corner cases.
>>>>> - The code to recreate the zk metadata for my application is super
>>>>> complex: if you decide to code against zk, it is good to think whether
>>>>> reconstructing in the case of a disaster is doable and if it is design
>>>>> and implement to reconstruct the state upon a disaster.
>>>>> Also, we typically provision enough replicas, often replicating across
>>>>> data centers, to make sure that the data isn't all gone. Having more
>>>>> replicas does not rule out completely the possibility of a disaster,
>> but
>>>>> in such rare cases we resort to the expensive path.
>>>>> I personally have never worked with an application that was taking
>>>>> backups of zk data in prod, so I'm really interested in what others
>>>>> think.
>>>>> -Flavio
>>>>>> On 16 Jun 2016, at 00:43, Jordan Zimmerman <
>> jordan@jordanzimmerman.com
>>>>>> wrote:
>>>>>> FYI - I wrote a blog about backing up ZooKeeper:
>>>>>> https://www.elastic.co/blog/zookeeper-backup-a-treatise
>>>>>> -Jordan

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