Adaptive Compression in Inverted Indexes: What Actually Happens Inside Lucene, Elasticsearch, and Tantivy

TL;DR: The thing that broke my mental model first wasn't slow queries — it was watching disk I/O climb to 95% utilization on NVMe drives while average query latency jumped from 12ms to 340ms on a corpus I'd carefully tuned for months. We were running Elasticsearch 8. 📖 Reading time: ~41 min The Pr