$_SERVER[HTTP_CACHE_CONTROL] set to NO CACHE always even though cache on

I checked $_SERVER['HTTP_CAC开发者_StackOverflowHE_CONTROL'] and it is saying no cache even though i have the meta tag:

<meta http-equiv="Cache-control" content="public">

and I've tried this as well

<meta http-equiv="Cache-control" content="cache">

still saying same "No CACHE"

Should I be worried that search engine spider gets same value as $_SERVER?

That value refers to the Cache-Control HTTP header sent in the request, i.e. the client sent this information to you. You have no control over it, but it doesn't have any real influence on your server either.