On 10/5/2018 4:41 AM, padmanabhan1616 wrote:
1. We cannot upgrade directly from 5.x to 7.x instead upgrade to 5.5 then upgrade to 7 as there is major index format level changes taken place in 5.5 or later version.
Solr 7.x cannot read indexes from 5.5. It can only read indexes that were *fully* constructed by versions back to 6.0.0.
1. Use index upgrade tool which can allow to upgrade all old indexes to new index format then we can upgrade to 7.x version easily.
We have been advised by Lucene experts that if a version that's at least two major versions before the target version has *EVER* touched the index, there's no guarantee that the index will work even after upgrading through the major versions one by one. The compatibility guarantee only goes back one major version.
I would strongly recommend with ANY upgrade that you always build the index from scratch. That produces the best results.
This is becoming a frequently asked question, so I have built a wiki page to answer it:
https://wiki.apache.org/solr/VersionCompatibility Thanks, Shawn
