Incremental updates and deletes, propagation lag, reindexing without downtime, and keeping an index honest about what no longer exists.
3 questions in RAG, Retrieval & Agents.
Detect change at the source rather than by re-crawling everything, upsert at document granularity so moved chunk boundaries do not orphan rows, propagate deletions as explicit tombstones the query filter respects, and publish the source-to-searchable lag as a measured SLA.
Ask the index directly whether the old text is still there, because that single check splits the problem into change detection, queue or write failure, a retire step that left duplicate chunks, or a downstream cache. Then fix the reason you learned about it from a user rather than an alert.
Build a shadow index beside the live one, dual-write from a recorded change-feed watermark so it never falls behind, verify on reconciliation counts plus a gold set and shadowed production queries, then cut over by moving an alias and keep the old index writable long enough to roll back.