What is near-real-time search in Elasticsearch?

Elasticsearch is described as near-real-time (NRT) because there is a small delay (by default, 1 second) between when a document is indexed and when it becomes visible in search results. This delay is caused by the refresh interval: Elasticsearch buffers writes in memory and periodically writes them to a new Lucene segment, making them searchable. The default refresh_interval is "1s", which is usually imperceptible to users. You can force an immediate refresh with the ?refresh=true parameter on index/update/delete requests, though this should be avoided in high-throughput scenarios.