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From Salman Akram <>
Subject Re: Master - Master / Upgrading a slave to master
Date Thu, 11 Sep 2014 09:33:30 GMT

On Tue, Sep 9, 2014 at 8:20 PM, Salman Akram <> wrote:

> So realistically speaking you cannot have SolrCloud work for 2 data
> centers as a redundant solution because no matter how many nodes you add
> you still would need at least 1 node in the 2nd center working too.
> So that just leaves with non-SolrCloud solutions.
> "1) Change the replication config to redefine the master and reload the core
> or restart Solr."
> That of course is a simple way but the real issue is about the possible
> issues and some good practices e.g. normally the scenario would be that
> primary data center goes down for few hours and till then we upgrade one of
> the slaves in secondary to a master. Now
> - IF there is no lag there won't be any issue in secondary at least but
> what if there is lag and one of the files is not completely replicated?
> That file would be discarded or there is a possibility that whole index is
> not usable?
> - Once the primary comes back how would we now copy the delta from
> secondary? Make it a slave of secondary first, replicate the delta and then
> set it as a master again?
> In other words is there a good guide out there for this with possible
> issues and solutions? Definitely before SolrCloud people would be doing
> this and even now SolrCloud doesn't seem practical in quite a few
> situations.
> Thanks again!!
> On Tue, Sep 9, 2014 at 8:02 PM, Shawn Heisey <> wrote:
>> On 9/9/2014 8:46 AM, Salman Akram wrote:
>> > You mean 3 'data centers' or 'nodes'? I am thinking if we have 2 nodes
>> on
>> > primary and 1 in secondary and we normally keep the secondary down would
>> > that work? Basically secondary network is just for redundancy and won't
>> be
>> > as fast so normally we won't like to shift traffic there.
>> >
>> > So can we just have nodes for redundancy and NOT load balancing i.e. it
>> has
>> > 3 nodes but update is only on one of them? Similarly for the slave
>> replicas
>> > can we limit the searches to a certain slave or it will be auto
>> balanced?
>> >
>> > Also apart from SOLR cloud is it possible to have multiple master in
>> > or a good guide to upgrade a slave to master?
>> You must have three zookeeper nodes for a redundant setup.  If you only
>> have two data centers, then you must put at least two of those nodes in
>> one data center.  If the data center with two zookeeper nodes goes down,
>> zookeeper cannot function, which means SolrCloud will not work
>> correctly.  There is no way to maintain SolrCloud redundancy with only
>> two data centers.  You might think to add a fourth ZK node and split
>> them between the data centers ... except that in that situation, at
>> least three nodes must be functional.  Two out of four nodes is not
>> enough.
>> A minimal fault-tolerant SolrCloud install is three physical machines.
>> Two of them run ZK and Solr, one of them runs ZK only.
>> If you don't use SolrCloud, then you have two choices to switch masters:
>> 1) Change the replication config to redefine the master and reload the
>> core or restart Solr.
>> 2) Write scripts that manually use the replication HTTP API to do all
>> your replication, rather than let Solr handle it automatically.  You can
>> choose the master for every replication with HTTP calls.
>> Thanks,
>> Shawn
> --
> Regards,
> Salman Akram


Salman Akram

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