[jira] [Commented] (TS-145) clarify cache.config actions in admin doc

["Hung Nguyen (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/TS-145?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13092723#comment-13092723 ] 

Hung Nguyen commented on TS-145:
--------------------------------

I think we should clarify 3 concepts: ttl, pin and revalidate. 
TTL (Time to live) is maximum time a cache object is considered as fresh, after that time, no matter that object has been most recently accessed, TS will automatically send request (GET) to original server to get fresh response.
Revalidate: AFAIK, only stale response (which is cached by ATS) must be revalidated. Sometimes ATS caches an object then rewrite Cache-Control header. Although client requests same object without specify Cache-Control: max-age header, cache object was stale already. Then the revalidate=time desires when a stale response should be revalidated before serving client request. In your example, TS will send request with If-Match or If-Not-Modified to original server, if html object is unchanged, original server will reply with 304 Not Modified and cache object is consider as fresh again. Otherwise, TS receives full response from origin server.
Cache pinning: when we use some cache algo like LRU, MRU, PLRU... some cache objects will be removed from cache memory when it's filled. In some case, we dont want special objects to be deleted from cache memory, even when ram (disk) is full, or that object is marked stale, we use pin-in-cache. It means every object is mark with regex url_regex=example.com/documents/article\d+.html will not be delete no matter what happened after 6 hours.




> clarify cache.config actions in admin doc
> -----------------------------------------
>
>                 Key: TS-145
>                 URL: https://issues.apache.org/jira/browse/TS-145
>             Project: Traffic Server
>          Issue Type: Improvement
>          Components: Documentation
>            Reporter: Miles Libbey
>            Priority: Minor
>             Fix For: Doc 3.0
>
>
> The differences between the actions in http://incubator.apache.org/trafficserver/docs/admin/files.htm#48049 don't seem very clear to me.  I don't understand the difference between:
> pin-in-cache
> revalidate
> ttl-in-cache
> Perhaps we could explain what different behaviors would happen if these settings (individually) entered
> url_regex=example.com/documents/article\d+.html pin-in-cache=6h 
> url_regex=example.com/documents/article\d+.html revalidate=6h 
> url_regex=example.com/documents/article\d+.html ttl-in-cache=6h 

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