> > > If you use N=3, W=3, R=1 in Cassandra, you > > > should get similar behavior > > > to HBase/HDFS with respect to consistency > > > and availability > > > > My understanding is that R=1 does not guarantee that you won't see > > different versions of the data in different reads, in some scenarios. > > Since this is fairly off-topic at this point, I'll keep it short. > The simple rule for Dynamo goes like this: if (R+W>N && W>=Quorum), > then you're guaranteed a consistent result always.
Ok, I'll concede this point rather than go really off-topic with conjecture about corner cases, especially given I'm not a Cassandra expert by any means and could simply be mistaken. However this is still not quite HBase-equivalent consistency. HBase can provide CAS operations and atomic counters because only one regionserver at a time can mediate operations on a given row. Best regards, - Andy Problems worthy of attack prove their worth by hitting back. - Piet Hein (via Tom White) From: Time Less <timelessn...@gmail.com> To: user@hbase.apache.org; Andrew Purtell <apurt...@apache.org> Sent: Wednesday, August 31, 2011 1:47 PM Subject: Re: HBase and Cassandra on StackOverflow > > If you use N=3, W=3, R=1 in Cassandra, you > should get similar behavior > > to HBase/HDFS with respect to consistency > and availability > > My understanding is that R=1 does not guarantee that you won't see > different versions of the data in different reads, in some scenarios. There > was an excellent Quora answer in this regard, I don't remember it offhand, > perhaps you can find the link to it or someone can provide it to you. > Since this is fairly off-topic at this point, I'll keep it short. The simple rule for Dynamo goes like this: if (R+W>N && W>=Quorum), then you're guaranteed a consistent result always. You get eventual consistency if W>=Quorum. If W<Quorum, then you can get inconsistent data that must be detected/fixed by readers (often using timestamps or similar techniques). Joe is right, enforcing (W=3, R=1, N=3) on a Dynamo system gives the same (provably identical?) behaviour as HBase, with respect to consistency. -- Tim Ellis Data Architect, Riot Games
