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 > > >
