Re: DCAwareRoundRobinPolicy question

[Justin Cameron]

Hi Nicu,

By default (with those lines commented), your application will only read
data from the local datacenter.

If you get different results when those lines are uncommented it means that
the data is not consistent between your datacenters. You'll need to run a
full repair to ensure that the data is consistent across both datacenters.

For your migration you should join the new DC, run a full repair, then
switch your applications over to the new DC (i.e. change withLocalDc()).
You can then safely decommission the nodes in your original DC.

I would recommend doing the repair one node at a time (sub-range repair
would be even better), to allow you to better control the process and limit
the potential performance impact on your applications.

Justin

On Tue, 6 Mar 2018 at 23:18 Marasoiu, Nicu 
wrote:

> Hi,
> We normally use a single data center, but when switching from one to
> another we will temporarily have two. The applications works with the local
> DC part of the cluster.
> Normally the configuration of the driver would contain (the commented
> lines absent):
>
> .withLoadBalancingPolicy(DCAwareRoundRobinPolicy.builder()
> .withLocalDc(localDataCenter)
> //  .withUsedHostsPerRemoteDc(3)
> //  .allowRemoteDCsForLocalConsistencyLevel()
> .build())
>
> However, the queries returned empty. Uncommenting the lines, the queries
> returned data. Multiple runs on multiple apps in multiple locations/dcs,
> gave data with lines commented/absent.
>
> All these apps connect to a cassandra cluster within a single data center
> currently. We are not clear why the empty results happened. Do you have any
> idea what might have caused this?
> Having the commented lines uncommented is dangerous in the context of how
> the data center migration is planned, since the queries would be able to
> reach the remote nodes which are not having all the data initially.
>
> Please advise,
> Thanks,
> Nicu Marasoiu
> Geschäftsanschrift/Business address: METRO SYSTEMS GmbH, Metro-Straße 12,
> 40235 Düsseldorf, Germany
> 
> Aufsichtsrat/Supervisory Board: Heiko Hutmacher (Vorsitzender/ Chairman)
> Geschäftsführung/Management Board: Dr. Dirk Toepfer (Vorsitzender/CEO),
> Wim van Herwijnen
> Sitz Düsseldorf, Amtsgericht Düsseldorf, HRB 18232/Registered Office
> Düsseldorf, Commercial Register of the Düsseldorf Local Court, HRB 18232
>
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*Justin Cameron*Senior Software Engineer





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DCAwareRoundRobinPolicy question

[Marasoiu, Nicu]

Hi,
We normally use a single data center, but when switching from one to another we 
will temporarily have two. The applications works with the local DC part of the 
cluster.
Normally the configuration of the driver would contain (the commented lines 
absent):

.withLoadBalancingPolicy(DCAwareRoundRobinPolicy.builder()
.withLocalDc(localDataCenter)
//  .withUsedHostsPerRemoteDc(3)
//  .allowRemoteDCsForLocalConsistencyLevel()
.build())

However, the queries returned empty. Uncommenting the lines, the queries 
returned data. Multiple runs on multiple apps in multiple locations/dcs, gave 
data with lines commented/absent.

All these apps connect to a cassandra cluster within a single data center 
currently. We are not clear why the empty results happened. Do you have any 
idea what might have caused this?
Having the commented lines uncommented is dangerous in the context of how the 
data center migration is planned, since the queries would be able to reach the 
remote nodes which are not having all the data initially.

Please advise,
Thanks,
Nicu Marasoiu
Geschäftsanschrift/Business address: METRO SYSTEMS GmbH, Metro-Straße 12, 40235 
Düsseldorf, Germany
Aufsichtsrat/Supervisory Board: Heiko Hutmacher (Vorsitzender/ Chairman)
Geschäftsführung/Management Board: Dr. Dirk Toepfer (Vorsitzender/CEO), Wim van 
Herwijnen
Sitz Düsseldorf, Amtsgericht Düsseldorf, HRB 18232/Registered Office 
Düsseldorf, Commercial Register of the Düsseldorf Local Court, HRB 18232

Betreffend Mails von *@metrosystems.net
Die in dieser E-Mail enthaltenen Nachrichten und Anhänge sind ausschließlich 
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oder zum Empfang dieser E-Mail nicht berechtigt sind, ist die Verwendung, 
Vervielfältigung oder Weitergabe der Nachrichten und Anhänge untersagt. Falls 
Sie diese E-Mail irrtümlich erhalten haben, informieren Sie bitte unverzüglich 
den Absender und vernichten Sie die E-Mail.

Regarding mails from *@metrosystems.net
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protected by professional secrecy. Unless you are the named addressee (or 
authorised to receive for the addressee) you may not copy or use this message 
or any attachment or disclose the contents to anyone else. If this e-mail was 
sent to you by mistake please notify the sender immediately and delete this 
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