The dataset concept is useful for grouping files and directories into manageable chunks. At its simplest, a dataset may be thought of as simply a toplevel directory. Regular expression support is available to define more sophisticated groupings, according to requirement.
The cache structure is updated with another layer, dataset, to accelerate processing of filter-by-dataset. Also, the cache filelist format is updated (removed user field, which may be inferred from parent directory). In short, the cache has undergone a breaking change. Rebuild your cache.