# Hit\_cache\_size,hit\_cache\_ttl not working

**URL:** <https://discuss.elastic.co/t/hit-cache-size-hit-cache-ttl-not-working/178026>\
**Category:** Logstash\
**Created:** [April 23, 2019, 11:32am UTC](https://discuss.elastic.co/t/hit-cache-size-hit-cache-ttl-not-working/178026 "2019-04-23T11:32:33Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Smack\_Alpha](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/smack_alpha/32/43660_2.png) [@Smack\_Alpha](https://discuss.elastic.co/u/Smack_Alpha)\
**Post date:** [April 23, 2019, 11:32am UTC](https://discuss.elastic.co/t/hit-cache-size-hit-cache-ttl-not-working/178026/1 "2019-04-23T11:32:34Z")

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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:

> |website|n|  
> |www.google.com|n1|  
> |www.yahoo.com|n2|  
> |www.bing.com|n3|  
> |www.stackoverflow.com|n4|  
> |www.smackcoders.com|n5|  
> |www.zoho.com|n6|  
> |www.quora.com|n7|  
> |www.elastic.co|n8|

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"
> }
> stdout{}
> }
> 
> ```

Here's the sample data passing through logstash:

> ```
> {
> "@version" => "1",
> "path" => "/home/paulsteven/log_cars/cars_dns.csv",
> "website" => "104.28.5.86",
> "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

---

<div class="post-metadata">

**Author:** ![Badger](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/badger/32/25190_2.png) [@Badger](https://discuss.elastic.co/u/Badger)\
**Post date:** [April 23, 2019, 12:07pm UTC](https://discuss.elastic.co/t/hit-cache-size-hit-cache-ttl-not-working/178026/2 "2019-04-23T12:07:39Z")

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> [@Smack\_Alpha](#):
>
> I want to know about "hit\_cache\_size". What is the use of it.

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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<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [May 21, 2019, 12:07pm UTC](https://discuss.elastic.co/t/hit-cache-size-hit-cache-ttl-not-working/178026/3 "2019-05-21T12:07:48Z")

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