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From Walter Underwood <>
Subject Re: SolrCould read-only replicas
Date Thu, 02 Oct 2014 16:12:06 GMT
Here is a different approach.

Set up independent Solr Cloud clusters in each data center. Send all updates into a persistent
message queue (Amazon SQS, whatever) and have each cluster get updates from the queue.

The two clusters are both live and configured identically, so there is nothing to change in
a failover.

Walter Underwood

On Oct 2, 2014, at 7:07 AM, Sandeep Tikoo <> wrote:

> Erick,
> Thank you for your response. Yup, when I said it is not possible to have a cross continent
data center replica, I meant that we never ever want to do that because of the latency.
> What I was hoping is that  I could have Solr cloud in my DataCentre A (DC-A) and get
all the benefits of sharding ( scaling/parallel computing) and failover redundancy within
the same data center. If I could then have a read-only replica (with no guaranteed consistency
of course ) of this entire cloud in my DataCenter B (DC-B), that would make my reads over
DC-B faster without making my writes slow. To clarify, all the writes were going to go against
DC-A only. The read-only cluster in DC-B could  also be made the master in case the entire
DC-A went down.  The DC-B wouldn't be guaranteed to be in sync with the DB-A master but in
my use case I could live with that. Seems like that is no possible out-of-the-box if I am
using Solr 4.0+ in the cloud mode. It is either Solr Coud or cross data center read only replica.
Can't do both at the same time.
> I think that is what you confirmed as well. If I have it wrong, please let me know. Also,
any thoughts on the most easy way to accomplish the read-only replica of the entire solr cloud
> Thanks!
> Tikoo
> From: Sandeep Tikoo
> Sent: Saturday, September 27, 2014 9:43 PM
> To: ''
> Subject: SolrCould read-only replicas
> Hi-
> I have been reading up on SolrCloud and it seems that it is not possible to have a cross-datacenter
read-only slave anymore but wanted to ask here to be sure.
> We currently have a pre Solr 4.0 installation with the master instance in our US mid-west
datacenter. The datacenter in Europe has read-replicas which pull data using solr.ReplicationHandler.
We wanted to upgrade to SolrCloud. As far as I have been able to figure out, with SolrCloud
you cannot have a read-only replica anymore. A replica has to be able to become a leader and
writes against all replicas for a shard have to succeed. Because of the a strong consistency
model across replicas, it seems that replicas cannot be across datacenters anymore.
> So my question is, how can we have a read-ony replica in a remote datacenter in Solr
4.0+ similar to pre Solr 4.0? Is it not possible anymore without doing it all yourself?
> cheers,
> Tikoo

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