NOTE
Elasticsearch Refresh
Near-real-time search visibility, refresh intervals, and why refresh is not a durability guarantee.
This is a historical learning note and may contain outdated or incomplete understanding.
A refresh makes recent index changes available to search by opening a new search-visible Lucene view/segment state. This is why Elasticsearch is described as near-real-time rather than instantly search-consistent after every write.
Refresh does not by itself guarantee durable persistence to disk; durability is handled through transaction-log/Lucene commit mechanisms.
Lowering the refresh interval increases search freshness but can increase segment creation/merge overhead. Tune freshness against indexing throughput and query requirements.