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From Ken Hancock <ken.hanc...@schange.com>
Subject Re: Decommissioning a datacenter deletes the data (on decommissioned datacenter)
Date Thu, 07 Aug 2014 18:27:56 GMT
My reading is it didn't forget the schema.  It lost the data.

My reading is decomissioning worked fine.  Possibly when you changed the
replication on a keyspace to include a second data center, the data didn't
get replicated.

When you ADD a datacenter, you need to do a nodetool rebuild to get the
data streamed to the new data center.  When you alter a keyspace to include
another datacenter in its replication schema, a nodetool repair is required
-- was this done?
http://www.datastax.com/documentation/cql/3.0/cql/cql_using/update_ks_rf_t.html

When you use nodetool decomission, you're effectively deleting the
parititioning token from the cluster.  The node being decommissioned will
stream its data to the new owners of its original token range.  This
streaming in no way should affect any other datacenter because you have not
changed the tokens or data ownership for any datacenter but the one in
which you are decomissioning a node.

When you eventually decomission the last node in the datacenter, all data
is gone as there are no tokens in that datacenter to own any data.

If you had a keyspace that was only replicated within that datacenter, that
data is gone (though you could probably add nodes back in and ressurect it).

If you had a keyspace where you changed the replication to include another
datacenter, if that datacenter had never received the data, then it may
have the schema but would have none of the data (other than new data that
was written AFTER you change the replication).




On Thu, Aug 7, 2014 at 2:11 PM, srmore <comomore@gmail.com> wrote:

>
>
>
> On Thu, Aug 7, 2014 at 12:27 PM, Robert Coli <rcoli@eventbrite.com> wrote:
>
>> On Thu, Aug 7, 2014 at 10:04 AM, srmore <comomore@gmail.com> wrote:
>>
>>> Sorry for being ambiguous.  By "deletes" I mean that running
>>> decommission I can no longer see any keyspaces owned by this node or
>>> replicated by other nodes using the cfstats command. I am also seeing the
>>> same behavior when I remove a single node from a cluster (without
>>> datacenters).
>>>
>>
>> I'm still not fully parsing you, but clusters should never "forget"
>> schema as a result of decommission.
>>
>> Is that what you are saying is happening?
>>
>
> Yes, this is what is happening.
>
>
>>
>> (In fact, even the decommissioned node itself does not forget its schema,
>> which I personally consider a bug.)
>>
>
>
> Ok, so I am assuming this is not a normal behavior and possibly a bug  -
> is this correct ?
>
>
>>
>> =Rob
>>
>>
>


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