Logstash IdentityMapCodec has reached 80% capacity"

{:timestamp=>"2016-05-18T09:54:51.819000+0100", :message=>"IdentityMapCodec has reached 80% capacity", :current_size=>16763, :upper_limit=>20000, :level=>:warn}

This error printing in the logstash log file continuosly how to avoid it.
Thanks in advance

Can you provide your config?