Elasticsearch supports partial document updates: https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-update.html
This might come in handy in cases where:
1) we know exactly what will change in the document
2) some fields are very expensive to generate (for instance with Tika)
It's a bit hard to say when condition #1 is reached right now, because:
a bridge may not declare all the fields it can generate (for instance with dynamic mapping)
multiple bridges may affect the same field
Maybe we can remove those grey areas in Hibernate Search 6.
Note: we may want to consider this feature for the Lucene integration, too.