Lucene has never promised that it will work correctly over _two_ major versions. IndexUpgraderTool simply optimizes into a single segment, which has it’s own problems (https://lucidworks.com/post/segment-merging-deleted-documents-optimize-may-bad/). It does _not_ transform the index to look like it had been exactly as if it had been written by the current version.
There’s a lot of discussion as to why Lucene _cannot_ upgrade the index which boils down to the fact that Lucene is a lossy abstraction so when upgrading you don’t have the original inputs, and if the calculations for what actually goes into the index change you can’t recompute them. In fact, starting with version 8, Lucene will refuse to open an index _ever touched_ by version X-2. The net-net is that you really have to re-index your data, painful as it might be to upgrade over two major versions of Lucene/Solr. Best, Erick > On Dec 3, 2019, at 3:57 AM, Yogesh Chaudhari > <yogesh.chaudh...@harbingergroup.com.INVALID> wrote: > > > Hi All, > > Since 2015 we are using Solr cloud for search. We are using Solr 5.2.1 now we > want to upgrade Solr 5.2.1 to Solr 7.7.2. Along with Solr we are using > Zookeeper 3.4.6 and wanted to upgrade it to Zookeeper 3.4.10. We have huge > data stored in existing Solr and need to maintained while migrating to Solr > 7.7.1. > > We have installed Solr 5.2.1 & Zookeeper 3.4.6 on windows server, for > installation we have used NSSM tools. We have installed 3 Zookeeper on 3 > instances , 6 shards and 9 solr nodes on 3 different instances. > > Can you please share procedure to upgrade Solr 5.2.1 to Solr 7.7.2 on windows > without affecting existing solr data (want to maintained)? > > Thanks, > > Yogesh Chaudhari >
