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From Erick Erickson <>
Subject Re: Migration from Solr 4
Date Tue, 18 Oct 2016 19:48:01 GMT
bq: ...whether it's OK to just copy the data files between 4.3 and 6.x

NOT ok. Solr (well, Lucene really) guarantees to read _one_ major version
behind. So a Solr 5x will read a solr 4x. But a Solr 6x is not guaranteed
at all to read a 4x.  And in fact removing back-compat complexification is
one of the benefits of moving to a new major version.

You can use the 5x IndexUpgraderTool to migrate from 4x->5x, then run
6x over the upgraded index.

All that said, I completely agree with John's advice to re-index entirely
from scratch if at all possible.

It's perfectly possible to run with a single Zookeeper. The quorum
formula is N/2 + 1. If you only have 1 ZK node, then 1 represents
quorum. It's just not advisable. Zk is responsible for presenting the
cluster topology to the entire set of Solr instances, you want it
to be robust so 3 is the recommended minimum. BTW, It's quite rare
to need more than that unless you're at pretty massive scale (hundreds
of Solr instances and/or collections), and even in these cases it's
usually best to use Observers....


On Tue, Oct 18, 2016 at 2:28 PM, John Bickerstaff
<> wrote:
> For what it's worth, (and it may not work for your situation) I decided not
> to upgrade, but to "upgrade by replacing".  In other words, I just
> installed 6.x and because I had set up my configs for "include" I didn't
> have to worry about what would be different about the "new" solrconfig.xml
> and the managed_schema file.  Instead, I was able to use a copy from one of
> the sample projects and add my "included" configs.
> Then, after creating the same collection structure in 6.x that I had in my
> 5.x instances, I just re-indexed everything into the new 6.x Solr.
> The big deal (probably) is whether it will cost you days to re-index and
> whether you have the resources to do that.
> I don't know if the index remained the same because I didn't have to
> trouble myself with that due to the replacement.  I'm sure others on the
> list can tell us whether it's OK to just copy the data files between 4.3
> and 6.x  (I'd guess not...)
> By the way - unless I misunderstand the Zookeeper docs, you can't get away
> with any less than 3 Zookeeper nodes. So keep that in mind.
> I have my rough notes about what I did available online.  You can go here
> for the link...
> On Tue, Oct 18, 2016 at 11:28 AM, sputul <> wrote:
>> We are using Solr 4.3, sing Zoopeeker on development manage Solr Cloud
>> having
>> one or two nodes. Will it be easier to migrate to Solr 5 first or should I
>> migrate to Solr 6 directly? I see Core definition has changed. Anything
>> else
>> worth noting?
>> The goal is to also use HTTPS perhaps after everything works in my local
>> environment using Single Zookeeper and a one or more Solr Nodes. Thanks.
>> --
>> View this message in context: http://lucene.472066.n3.
>> Sent from the Solr - User mailing list archive at

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