Interesting article, though it leaves me wondering which changes or sets of changes caused the problematic variations in behavior.
On Thu, Mar 12, 2026 at 3:18 AM Parveen Saini <[email protected]> wrote: > Hi all, > > Following up on the earlier thread about the migration validation approach > for major Solr upgrades, I wrote up the full story and lessons learned from > the Solr 5 to 8 migration we discussed. > > Sharing here in case it’s useful for others planning similar upgrades: > https://dzone.com/articles/solr5-to-solr8-migration-ads-system > > Best, > Parveen > > On Sat, Feb 28, 2026 at 9:17 AM Parveen Saini <[email protected] > > > wrote: > > > Hi all, > > > > While migrating a production system from Solr 5 to 8, we encountered > > subtle ranking drift that did not surface in standard upgrade testing. > The > > system functioned correctly, but ranking behavior changed in non obvious > > ways. We observed score distribution shifts, candidate set differences > > influenced by negative score handling, and p99 latency regressions. > > > > Using that migration as a real world case, I put together a small side by > > side validation harness designed to make behavioral differences across > > major Solr versions observable. The goal is not to provide version > specific > > guidance, but to offer a structured approach for detecting ranking and > > performance drift during major upgrades. > > > > The harness compares docset overlap, score distributions, and query level > > behavior across versions. > > > > Sharing in case it is useful for others planning major Solr upgrades: > > https://github.com/parveensaini/solr-lucene-migration-correctness > > > > Happy to share more details or present the approach at an upcoming > > community meetup if there is interest. > > > > Thanks, > > Parveen > > > -- http://www.needhamsoftware.com (work) https://a.co/d/b2sZLD9 (my fantasy fiction book)
