OpenSearch Architecture Deep Dive & Splunk-to-OpenSearch Migration Guide
Principal engineering guide to OpenSearch internals (Apache Lucene segments, FSTs, DocValues, Segment Replication, ISM tiers) and end-to-end Splunk-to-OpenSearch migration (Schema-on-Read vs Schema-on-Write, SPL to PPL/DSL translation, Data Prepper pipelines, and capacity math).