Vary: ETag Extensions \\Sam  posts an interesting proposal.  This is better than the HTTP delta\suggestion but still has a few issues.\\The client needs to know the ETags before it can start performing differential\fetches.  With date ranges you still preserve the initial archive query.  For\example when you first subscribe to a feed you could fetch 30 days worth of\posts.  If you like the feed you can even fetch *older* posts which could be\really cool.  Also even if you still use faster checksum algorithm like CRC32 or\Adler32 you still have an O(N) performance hit for your document.  If you have a\btree on your post dates you will gave O(log(N)) for search for a much smaller\string (64bit in most situations).  F ...\\