This is controlled by the (Last-Modified, If-Modified-Since) and (ETag, If-None-Match) header pairs. HTTP is stateless; it does not require any persistence. The

This is controlled by the (Last-Modified, If-Modified-Since) and (ETag, If-None-Match) header pairs. HTTP is stateless; it does not require any persistence. The only thing that defines kind of an optional persistence is the caching layer, for obvious reasons.