Leave out default Logstash fields in ElasticSearch

Question

After processing data with: input | filter | output > ElasticSearch the format it's get stored in is somewhat like:

"_index": "logstash-2012.07.02",
"_type": "stdin",
"_id": "JdRaI5R6RT2do_WhCYM-qg",
"_score": 0.30685282,
"_source": {
    "@source": "stdin://dist/",
    "@type": "stdin",
    "@tags": [
        "tag1",
        "tag2"
    ],
    "@fields": {},
    "@timestamp": "2012-07-02T06:17:48.533000Z",
    "@source_host": "dist",
    "@source_path": "/",
    "@message": "test"
}

I filter/store most of the important information in specific fields, is it possible to leave out the default fields like: @source_path and @source_host? In the near future it's going to store 8 billion logs/month and I would like to run some performance tests with this default fields excluded (I just don't use these fields).

Answer 1

This removes fields from output:

filter {
    mutate {
        # remove duplicate fields
        # this leaves timestamp from message and source_path for source
        remove => ["@timestamp", "@source"]
    }
 }