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From Shawn Heisey <>
Subject Re: Mix Solr 4 and 5?
Date Fri, 22 Jan 2016 15:19:01 GMT
On 1/21/2016 11:57 PM, wrote:
> Long story short, we use a CMS that is integrated with Solr 4.6, with the solrj jar file
in the global/common Tomcat classpath. We currently use a Google Search Appliance machine
for our own freetext search needs, but plan to replace that with some other solution in the
near future. Since we already work with solr because of the CMS integration, we would like
to select solr for this project.
> But I would prefer to use the latest version, ie solr 5, and I am not sure how that would
work in our situation. Can we use the solrj client for solr 4 when indexing and searching
on a solr 5 server? If so, would we miss some important feature, and would this setup be future
> Or can we somehow use both solr4 and solr 5 client libraries at the same time, in the
same context? It is not possible to upgrade the solr server that the CMS is using, and it
is not possible to remove the 4.6 solrj jar from the common classpath in Tomcat. That is,
unless the solr 5 version of solrj is backwards compatible, so that we can switch the jar
files and our CMS would still be able to index and search in it's own solr 4 server.

If you are NOT running SolrCloud, then that should work with no
problem.  The HTTP API is fairly static and has not seen any major
upheaval recently.  If you're NOT running SolrCloud, you may even be
able to replace the SolrJ jar in your existing system with the 5.4.1
version (and update SolrJ's dependent jars) and have everything continue
to work.

If you ARE running SolrCloud, I would not try mixing 4.x and 5.x, in
either direction.  SolrCloud is evolving very quickly ... I wouldn't
even mix *minor* versions, much less *major* versions.  There are
differences in how the zookeeper database is laid out, and mixing
versions is not guaranteed to work, especially if SolrJ is older than
Solr.  If the version difference is small and SolrJ is newer than Solr,
there's a chance of success, but with the situation you have described,
SolrCloud would likely not work.

I have no idea about whether or not you can mix SolrJ versions in your
client project.  This is extremely tricky to get working right with Java
in general, and may not be possible.


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