I have tried below code it works fine but it uses TransportClient to delete all documents.
DeleteByQueryRequestBuilder deleteByQueryRequestBuilder = DeleteByQueryAction.INSTANCE.newRequestBuilder(transportClient)
.filter(QueryBuilders.matchAllQuery())
.source(indexName);
BulkByScrollResponse response = deleteByQueryRequestBuilder
.filter(QueryBuilders.matchAllQuery()).get()
I am using elasticsearch 6.1.4. What is the way to delete all documents from index using RestHighLevelClient.