Elasticsearch introduces two new features in its updates: _reindex and _update_by_query, designed to enhance data management capabilities. _reindex allows users to copy documents from one index to another, enabling document enrichment or index recreation to modify locked settings at creation. It facilitates both straightforward document copying and more complex operations like selective copying based on specific tags or adding new tags during the process. On the other hand, _update_by_query updates fields within documents in the same index and can accommodate online mapping changes, useful for tasks like adding new searchable fields. Both features, capable of handling millions of documents, can be monitored for progress and canceled if required, although cancelation doesn't roll back changes. While these features are powerful, they don't optimize resource efficiency and are better suited for transforming existing data rather than updating data post-ingestion.