Hit_cache_size,hit_cache_ttl not working

I am using dns filter in logstash for my csv file. in my csv file, i have two fields. they are website and count.
Here's the sample content of my csv file:


Here's my logstash config file:

input {
   file {
      path => "/home/paulsteven/log_cars/cars_dns.csv"
      start_position => "beginning"
      sincedb_path => "/dev/null"
filter {
    csv {
        separator => ","
        columns => ["website","n"]
    dns { 
      resolve => [ "website" ] 
      action => "replace" 
      hit_cache_size => 8000 
      hit_cache_ttl => 300 
      failed_cache_size => 1000 
      failed_cache_ttl => 10
output {
  elasticsearch {
    hosts => "localhost:9200"
    index => "dnsfilter03"
    document_type => "details"

Here's the sample data passing through logstash:

      "@version" => "1",
          "path" => "/home/paulsteven/log_cars/cars_dns.csv",
       "website" => "",
             "n" => "n21",
          "host" => "smackcoders",
       "message" => "www.smackcoders.com,n21",
    "@timestamp" => 2019-04-23T10:41:15.680Z

In the logstash config file, I want to know about "hit_cache_size". What is the use of it. I read the guide of dns filter but unable to figure it out. I added the field in my logstash config but nothing happened. can i get any examples for that. I want to know the use of hit_cache_size. What is the job it's doing in dns filter

Doing a DNS lookup can be expensive. For example, there are places in China where it takes 400 milliseconds for a round trip to Virginia in the USA. If it takes 400 milliseconds to do a DNS lookup then you can only process 2 or 3 events per second. The hit cache saves the result of the DNS lookup so that if you do the same lookup in the next 60 seconds it re-uses the previous result. It ignores the TTLs on A/PTR/NS records.

If you are doing lookups on a long list of unique domains it will give you no performance benefit because you never look up the same domain twice.

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