It seams that JIRA REST calls do not respect the HTTP protocol specification that states that a web resource has to report the "Last-Modified" date-time inside the header.

This is essential because this controls how HTTP caching works, a proper implementation would considerably speed-up JIRA and lower the load on the server too.

It seems that the same problem was reported and fixed for non-REST calls, but for REST calls it's still happening.

For example, if a REST call is made for a search using JQL, the server should return the Last-modified field of the newest changed Issue returned.

Also, when receiving a REST call with Last-Modified setup by the client, the JIRA server should first check the latest change for the returned query and to return 301 / Not Modified if it's the server side one is less or equal to the value being specified.