Shard Indexing Backpressure

Versions : 1.3.5

Describe the issue:

Hello,

We are looking into enabling shard_indexing_pressure.enforced, but we don’t really know the consequences of the request rejection, and it’s not clear in the documentation.

It will drop the logs, and they will get lost? Or it will return an error and the Log Shipper(logstash, filebeat, etc) will wait before trying to send again the logs?

It’s there any way to receive an alert/notification if a request was rejected from the index because of the shard indexing backpressure?