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
