Hello, Wanted to share an exciting development with the community. Recently Lucene PR https://github.com/apache/lucene/pull/15431 ("Revise strategy to open an index") got merged. This makes Lucene look at individual segments for backward compatibility rather than when the index was first created. Earlier this week Solr PR https://github.com/apache/solr/pull/3883 got merged which provides a merge policy to prevent older segments from merging. This should be available in the next Solr 9.x release. A combination of these PRs means if an index was created in Solr 8.x, and later upgraded to 9.x, users could upgrade to Solr 10.x in the future without having to completely rebuild the index from an external source as is the requirement today.
For indexes originally created in Solr 8.x, this enhancement would require them to reindex data in existing collections (onto the same collection) once they are on the upcoming Solr 9.x release, and works if the fields are stored or docValues true (or a copy field destination, if not stored); *without any downtime.* Rinse and repeat when they are on Solr 10.x, to prepare for upgrade to Solr 11. Thanks to Michael Sokolov and David Smiley for the review inputs and for the help in seeing this through! An upcoming PR is in the works which provides an /admin/cores REST endpoint that will do the reindexing automatically and in an optimized way by targeting only the data in older segments https://github.com/apache/solr/pull/3903 Thanks, Rahul Goswami
