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From Alexander Shraer <shra...@gmail.com>
Subject Re: Can I recover full zookeeper state from observer?
Date Thu, 07 Feb 2013 21:28:25 GMT

You can probably do this manually now, but I'll let someone else comment on

In 3.5.0 release (with ZK-107 in) you will be able to turn observers into
leader + followers and vise versa by running a simple zookeeper command.
But unfortunately not in the scenario you described.

In your scenario, there are two possible problems that make it unsafe to
- it possible that the connection between the datacenters is down and not
DC1, and therefore if DC2 independently decides
to start leading we may have "split brain" - both quorums will be
independently processing and committing operations.
- it is very possible that DC1 is down but managed to commit things before
it went
down which are unknown to DC2, and therefore if we activate DC2 we'll loose
committed state.

You will only be able to reconfigure if a quorum (majority) of the old
configuration and a quorum of the new configuration are up and connected to
the current leader.


On Thu, Feb 7, 2013 at 4:24 AM, Kuba Lekstan <kuebzky@gmail.com> wrote:

> Hello
> I'm considering situation when I have 2 data centers, In 1s DC I'm having
> leader + followers, in 2nd only observers.
> In case when my 1st DC goes down, can I somehow reconfigure observers in
> 2nd DC to leader+followers?
> From what I found out the observers doesn't get transaction logs from the
> leader, is there any option I could set to change this behavior?
> Thanks.

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