There is disclosed a data processing system and method for fetching a plurality of data frames for processing in succession at a desired rate. Data frames are fetched into available space in cache. A priority level is then assigned to each data frame by applying a recurring priority level pattern. A suitable priority level cut-off may be selected (e.g. based on available space in cache) and any data frames with a priority level below the priority level cut-off are dropped. Successive data frames having assigned priority levels above the priority level cut-off are selectively fetched into cache.