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Zookeeper >> mail # user >> Re: Efficient backup and a reasonable restore of an ensemble


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Flavio Junqueira 2013-07-08, 21:30
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Sergey Maslyakov 2013-07-08, 22:28
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Thawan Kooburat 2013-07-09, 00:53
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Re: Efficient backup and a reasonable restore of an ensemble
I think what we are looking at is a  point in time restore functionality.
How about adding a feature that says go back to a specific zxid/timestamp.
This way before doing any change to zookeeper simply note down the
timestamp/zxid on leader. If things go wrong after making changes, bring
down zookeepers and provide additional parameter of a zxid/timestamp while
restarting. The server can go the exact point and make it current. The
followers can be started blank.

On Mon, Jul 8, 2013 at 5:53 PM, Thawan Kooburat <[EMAIL PROTECTED]> wrote:

> Just saw that  this is the corresponding use case to the question posted
> in dev list.
>
> In order to restore the data to a given point in time correctly, you need
> both snapshot and txnlog. This is because zookeeper snapshot is fuzzy and
> snapshot alone may not represent a valid state of the server if there are
> in-flight requests.
>
> The 4wl command should cause the server to roll the log and take a
> snapshot similar to periodic snapshotting operation. Your backup script
> need grap the snapshot and corresponding txnlog file from the data dir.
>
> To restore, just shutdown all hosts, clear the data dir, copy over the
> snapshot and txnlog, and restart them.
>
>
> --
> Thawan Kooburat
>
>
>
>
>
> On 7/8/13 3:28 PM, "Sergey Maslyakov" <[EMAIL PROTECTED]> wrote:
>
> >Thank you for your response, Flavio. I apologize, I did not provide a
> >clear
> >explanation of the use case.
> >
> >This backup/restore is not intended to be tied to any write event,
> >instead,
> >it is expected to run as a periodic (daily?) cron job on one of the
> >servers, which is not guaranteed to be the leader of the ensemble. There
> >is
> >no expectation that all recent changes are committed and persisted to
> >disk.
> >The system can sustain the loss of several hours worth of recent changes
> >in
> >the event of restore.
> >
> >As for finding the leader dynamically and performing backup on it, this
> >approach could be more difficult as the leader can change time to time and
> >I still need to fetch the file to store it in my designated backup
> >location. Taking backup on one server and picking it up from a local file
> >system looks less error-prone. Even if I went the fancy route and had
> >Zookeeper send me the serialized DataTree in response to the 4wl, this
> >approach would involve a lot of moving parts.
> >
> >I have already made a PoC for a new 4wl that invokes takeSnapshot() and
> >returns an absolute path to the snapshot it drops on disk. I have already
> >protected takeSnapshot() from concurrent invocation, which is likely to
> >corrupt the snapshot file on disk. This approach works but I'm thinking to
> >take it one step further by providing the desired path name as an argument
> >to my new 4lw and to have Zookeeper server drop the snapshot into the
> >specified file and report success/failure back. This way I can avoid
> >cluttering the data directory and interfering with what Zookeeper finds
> >when it scans the data directory.
> >
> >Approach with having an additional server that would take the leadership
> >and populate the ensemble is just a theory. I don't see a clean way of
> >making a quorum member the leader of the quorum. Am I overlooking
> >something
> >simple?
> >
> >In backup and restore of an ensemble the biggest unknown for me remains
> >populating the ensemble with desired data. I can think of two ways:
> >
> >1. Clear out all servers by stopping them, purge version-2 directories,
> >restore a snapshot file on one server that will be brought first, and then
> >bring up the rest of the ensemble. This way I somewhat force the first
> >server to be the leader because it has data and it will be the only member
> >of a quorum with data, provided to the way I start the ensemble. This
> >looks
> >like a hack, though.
> >
> >2. Clear out the ensemble and reload it with a dedicated client using the
> >provided Zookeeper API.
> >
> >With the approach of backing up an actual snapshot file, option #1 appears
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Thawan Kooburat 2013-07-09, 03:09
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kishore g 2013-07-09, 04:05
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Sergey Maslyakov 2013-07-09, 04:42
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Ted Dunning 2013-07-09, 05:32
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kishore g 2013-07-09, 05:08
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Flavio Junqueira 2013-07-09, 09:12
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Sergey Maslyakov 2013-07-09, 16:02
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Ted Dunning 2013-07-09, 20:00
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Flavio Junqueira 2013-07-09, 16:47
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kishore g 2013-07-09, 17:01
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Flavio Junqueira 2013-07-09, 17:04
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Sergey Maslyakov 2013-07-09, 04:40
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Sergey Maslyakov 2013-07-09, 04:34
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Sergey Maslyakov 2013-07-09, 04:25
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jack ma 2013-07-16, 15:38