Logstash output-elasticsearch action "update" not work 4 me

[tonyjames3212 (Tony James)]

version:v5.3.0
https://www.elastic.co/guide/en/logstash/5.2/plugins-outputs-elasticsearch.html#plugins-outputs-elasticsearch-action
And my out put:

    elasticsearch {                                                                                                                                    
      action => "update"                                                                                                                               
      document_id => "%{dep_id}"                                                                                                                       
      hosts => ["localhost:9200"]                                                                                                                     
      index => "department"                                                                                                                    
      doc_as_upsert => true                                                                                                                            
    } 

My data is from the table department of Postgres 9.5 using the plugin input-jdbc.
The records can be indexed into ES.
Then I changed the field "department_name" of one record in PGSql,but no more update in ES?And there was no err/warning logs in logstash.

How should I change the configuration?
Any way,it works if I change the "update" to "delete".But it indeed can not be updated.
Any idea?