Retrieving a document at replica shard while it is not yet updated data

Question

I have a question with Elasticsearch as below:

In mode replication is async, while a document is being indexed, the document will already be present on the primary shard but not yet copied to the replica shards. At this time, a GET request for this document is forwarded to a replica shard.

How does Elasticsearch handle this in the cases the document is not yet indexed on the replica shards or the document is not yet updated on the replica shards ?

A fail request will be returned in the case indexing a new document or a old document returned in the case updating a document? Or requesting node will re-forward to the primary shard to get data?

Answer 1

First of all, I wouldn't recommend using the async mode. It doesn't really provides any benefits that you couldn't achieve in a safer way but creates issues when in comes to reliability. Because of this, this feature was deprecated in v1.5 and completely removed in v2.0 of elasticsearch.

Saying that, if you still want to use async and care about getting the latest results, you have to use it with primary preference.

In case of update operation, you don't have to do anything. Update is always performed on the primary shard first and then the result of the operation is replicated to all replicas.