For that aspect no difference between a String ring based on compareTo and a BigInteger one. The only difference (and it is an important one for the reasons I gave!) is how the compare works. But for the p2p aspect it does not matter.
On Wed, Apr 1, 2009 at 3:40 PM, Avinash Lakshman <[email protected]> wrote: > Doing what you are suggesting scares the hell out of me for a couple of > reasons - All work in P2P be it random/OPHF does the token handling the way > it is setup. I cannot try something that has not been well explored in > academia. I insist this must be doable. I am going to think about this more. > > Avinash > > On Wed, Apr 1, 2009 at 2:31 PM, Jonathan Ellis <[email protected]> wrote: > >> Avinash already commited his new order-preserving hash function and I >> missed it. It's in OrderPreservingHashPartitioner. It takes the >> approach that Todd and I discussed back in January: turn the string >> into a base-Char.MAX_VALUE number. >> ( >> http://groups.google.com/group/cassandra-dev/browse_thread/thread/6bda8518466210e7/f53b79c19010a9ed >> ). >> I chatted with Avinash a little on IM but we didn't finish, so I'm >> picking it up here. >> >> There are two problems with this approach. One is that the hashes >> will only be order-preserving for a subset of unicode (all of UCS-2, >> but not all of UTF-16; see http://en.wikipedia.org/wiki/UTF-16/UCS-2). >> The other is that this only gives you a naive ordering by code point >> value, which for unicode is not what you want and even for ascii >> sometimes you want another collation. (see >> http://www.unicode.org/reports/tr10/ and >> http://java.sun.com/javase/6/docs/api/java/text/Collator.html). >> >> Say for instance you have inserted keys ['a', 'b', '--a', '--b'] and >> you are going to do range queries on them. The correct >> collation-aware sort is ['a', '--a', 'b', '--b']. But ordering by >> char value gives ['--a', '--b', 'a', 'b']. >> >> Switching to a more flexibile system like the one I wrote for >> CASSANDRA-3 will let use use Token<BigInteger> for random distribution >> or Token<String> for order-preserving, with user-defined collation. I >> don't see a way to get this kind of flexibility from an approach that >> insists on turning everything into BigInteger. >> >> -Jonathan >> >> On Mon, Mar 30, 2009 at 2:16 PM, Jonathan Ellis <[email protected]> wrote: >> > Avinash, >> > >> > You mentioned that you have a new order-preserving hash function that >> > you think will be more generally useful. Can you post it? >> > >> > thanks, >> > >> > -Jonathan >> > >> >
