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From Daniel Collins <danwcoll...@gmail.com>
Subject Re: SolrCloud multiple data center support
Date Mon, 03 Feb 2014 22:16:21 GMT
Option a) doesn't really work out of the box, *if you need NRT support*.
 The main reason (for us at least) is the ZK ensemble and maintaining
quorum. If you have a single ensemble, say 3 ZKs in 1 DC and 2 in another,
then if you lose DC 2, you lose 2 ZKs and the rest are fine.  But if you
lose the main DC that has 3 ZKs, you lose quorum.  Searches will be ok, but
if you are an NRT-setup, your updates will all stall until you get another
ZK started (and reload the whole Solr Cloud to give them the ID of that new
ZK).

For us, availability is more important than consistency, so we currently
have 2 independent setups, 1 ZK ensemble and Solr Cloud per DC.  We already
had an indexing system that serviced DCs so we didn't need something like
Flume.  We also have external systems that handle routing to some extent,
so we can route "locally" to each Cloud, and not have to worry about
cross-DC traffic.

One solution to that is have a 3rd DC with few instances in, say another 2
ZKs. That would take your total ensemble to 7, and you can lose 3 whilst
still maintaining quorum.  Since ZK is relatively light-weight, that 3rd
"Data Centre" doesn't have to be as robust, or contain Solr replicas, its
just a place to house 1 or 2 machines for holding ZKs.  We will probably
migrate to this kind of setup soon as it ticks more of our boxes.

One other option is in ZK trunk (but not yet in a release) is the ability
to dynamically reconfigure ZK ensembles (
https://issues.apache.org/jira/browse/ZOOKEEPER-107).  That would give the
ability to create new ZK instances in the event of a DC failure, and
reconfigure the Solr Cloud without having to reload everything. That would
help to some extent.

If you don't need NRT, then the solution is somewhat easier, as you don't
have to worry as much about ZK quorum, a single ZK ensemble across DCs
might be sufficient for you in that case.


On 3 February 2014 17:44, Mark Miller <markrmiller@gmail.com> wrote:

> SolrCloud has not tackled multi data center yet.
>
> I don't think a or b are very good options yet.
>
> Honestly, I think the best current bet is to use something like Apache
> Flume to send data to both data centers - it will handle retries and
> keeping things in sync and splitting the stream. Doesn't satisfy all use
> cases though.
>
> At some point, multi data center support will happen.
>
> I can't remember where ZooKeeper's support for it is at, but with that and
> some logic to favor nodes in your data center, that might be a viable route.
>
> - Mark
>
> http://about.me/markrmiller
>
> On Feb 3, 2014, at 11:48 AM, Darrell Burgan <Darrell.Burgan@infor.com>
> wrote:
>
> > Hello, we are using Solr in a SolrCloud configuration, with two Solr
> instances running with three Zookeepers in a single data center. We
> presently have a single search index with about 35 million entries in it,
> about 60GB disk space on each of the two Solr servers (120GB total). I
> would expect our usage of Solr to grow to include other search indexes, and
> likely larger data volumes.
> >
> > I'm writing because we're needing to grow beyond a single data center,
> with two (potentially incompatible) goals:
> >
> > 1.       We need to be able to have a hot disaster recovery site, in a
> completely separate data center, that has a near-realtime replica of the
> search index.
> >
> > 2.       We'd like to have the option to have multiple active/active
> data centers that each see and update the same search index, distributed
> across data centers.
> >
> > The options I'm aware of from reading archives:
> >
> > a.       Simply set up the remote Solr instances as active parts of the
> same SolrCloud cluster. This will  essentially involve us standing up
> multiple Zookeepers in the second data center, and multiple Solr instances,
> and they will all keep each other in sync magically. This will also solve
> both of our goals. However, I'm concerned about performance and whether
> SolrCloud is smart enough to route local search queries only to local Solr
> servers ... ? Also, how does such a cluster tolerate and recover from network
> partitions?
> >
> > b.      The remote Solr instances form their own completely unrelated
> SolrCloud cluster. I have to invent some kind of replication logic of my
> own to sync data between them. This replication would have to be
> bidirectional to satisfy both of our goals. I strongly dislike this option
> since the application really should not concern itself with data
> distribution. But I'll do it if I must.
> >
> > So my questions are:
> >
> > -          Can anyone give me any guidance as to option a? Anyone using
> this in a real production setting? Words of wisdom? Does it work?
> >
> > -          Are there any other options that I'm not considering?
> >
> > -          What is Solr's answer to such configurations (we can't be
> alone in needing one)? Any big enhancements coming on the Solr road map to
> deal with this?
> >
> > Thanks!
> > Darrell Burgan
> >
> >
> >
> > Darrell Burgan | Chief Architect, PeopleAnswers
> > office: 214 445 2172 | mobile: 214 564 4450 | fax: 972 692 5386 |
> darrell.burgan@infor.com | http://www.infor.com
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>
>

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