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From Chris Nauroth <cnaur...@hortonworks.com>
Subject Re: FYI - Apache ZooKeeper Backup, a Treatise
Date Thu, 16 Jun 2016 19:39:15 GMT
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 a
>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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