I believe I heard someone talk at Cassandra SF conference about creating a partitioner that was a derivation of RandomPartitioner. It essentially would look for keys that adhere to a certain pattern, like <key>:<subkey>. The <key> portion would be used for determining the location on the ring, but <key>:<subkey> for actually storing. This would allow groups of data (all having the same <key>) to reside on the same node, while still maintaining uniqueness across the entire keyspace.
Unbalanced nodes could still occur, but I don't think any worse than wide/large rows can cause. On 11/8/11 1:29 AM, "Daniel Doubleday" <daniel.double...@gmx.net> wrote: >Ah cool - thanks for the pointer! > >On Nov 7, 2011, at 5:25 PM, Ed Anuff wrote: > >> This is basically what entity groups are about - >> https://issues.apache.org/jira/browse/CASSANDRA-1684 >> >> On Mon, Nov 7, 2011 at 5:26 AM, Peter Lin <wool...@gmail.com> wrote: >>> This feature interests me, so I thought I'd add some comments. >>> >>> Having used partition features in existing databases like DB2, Oracle >>> and manual partitioning, one of the biggest challenges is keeping the >>> partitions balanced. What I've seen with manual partitioning is that >>> often the partitions get unbalanced. Usually the developers take a >>> best guess and hope it ends up balanced. >>> >>> Some of the approaches I've used in the past were zip code, area code, >>> state and some kind of hash. >>> >>> So my question related deterministic sharding is this, "what rebalance >>> feature(s) would be useful or needed once the partitions get >>> unbalanced?" >>> >>> Without a decent plan for rebalancing, it often ends up being a very >>> painful problem to solve in production. Back when I worked mobile >>> apps, we saw issues with how OpenWave WAP servers partitioned the >>> accounts. The early versions randomly assigned a phone to a server >>> when it is provisioned the first time. Once the phone was associated >>> to that server, it was stuck on that server. If the load on that >>> server was heavier than the others, the only choice was to "scale up" >>> the hardware. >>> >>> My understanding of Cassandra's current sharding is consistent and >>> random. Does the new feature sit some where in-between? Are you >>> thinking of a pluggable API so that you can provide your own hash >>> algorithm for cassandra to use? >>> >>> >>> >>> On Mon, Nov 7, 2011 at 7:54 AM, Daniel Doubleday >>> <daniel.double...@gmx.net> wrote: >>>> Allow for deterministic / manual sharding of rows. >>>> >>>> Right now it seems that there is no way to force rows with different >>>>row keys will be stored on the same nodes in the ring. >>>> This is our number one reason why we get data inconsistencies when >>>>nodes fail. >>>> >>>> Sometimes a logical transaction requires writing rows with different >>>>row keys. If we could use something like this: >>>> >>>> prefix.uniquekey and let the partitioner use only the prefix the >>>>probability that only part of the transaction would be written could >>>>be reduced considerably. >>>> >>>> >>>> >>>> On Nov 1, 2011, at 11:59 PM, Jonathan Ellis wrote: >>>> >>>>> Hi all, >>>>> >>>>> Two years ago I asked for Cassandra use cases and feature requests. >>>>> [1] The results [2] have been extremely useful in setting and >>>>> prioritizing goals for Cassandra development. But with the release >>>>>of >>>>> 1.0 we've accomplished basically everything from our original wish >>>>> list. [3] >>>>> >>>>> I'd love to hear from modern Cassandra users again, especially if >>>>> you're usually a quiet lurker. What does Cassandra do well? What >>>>>are >>>>> your pain points? What's your feature wish list? >>>>> >>>>> As before, if you're in stealth mode or don't want to say anything in >>>>> public, feel free to reply to me privately and I will keep it off the >>>>> record. >>>>> >>>>> [1] >>>>>http://www.mail-archive.com/cassandra-dev@incubator.apache.org/msg0114 >>>>>8.html >>>>> [2] >>>>>http://www.mail-archive.com/cassandra-user@incubator.apache.org/msg014 >>>>>46.html >>>>> [3] >>>>>http://www.mail-archive.com/dev@cassandra.apache.org/msg01524.html >>>>> >>>>> -- >>>>> Jonathan Ellis >>>>> Project Chair, Apache Cassandra >>>>> co-founder of DataStax, the source for professional Cassandra support >>>>> http://www.datastax.com >>>> >>>> >>> >
