Merge branch 'master' into next

kong/tools/database_cache.lua

@@ -125,6 +125,10 @@ function _M.delete_all()
 end
 
 -- Retrieves a piece of data from the cache or loads it.
+-- **IMPORTANT:** the callback function may not exit the request early by e.g.
+-- sending a 404 response from the callback. The callback will be nested inside
+-- lock/unlock calls, and hence it MUST return or the lock will not be
+-- unlocked. Which in turn will lead to deadlocks and timeouts. 
 -- @param key the key under which to retrieve the data from the cache
 -- @param ttl time-to-live for the entry (in seconds)
 -- @param cb callback function. If no data is found under `key`, then the callback