Logstash duplicate line / send log with elasticsearch:9200 no response


I use Logstash with CSV files sources.
What happens if logstash can not contact ElasticSearch on 9200 port.
They sent the logs will be reissued , or the logs are lost ?

Dy ou know a concept of primary key to reject duplicates lines ?
I find in another topic a system of hash Logstash Duplicate message


This should explain that part - https://www.elastic.co/guide/en/logstash/current/pipeline.html