The Datastax post on counters says: "Prior to 0.8, Cassandra had no simple and efficient way to count. By “counting,” we mean here to provide an atomic increment operation in a single column value, as opposed to counting the number of columns in a row, or rows in a column family, both of which were already supported."
So, maybe there's a way you can count the # of columns in the row in the application side before you create a new column. You'll pretty much have to add the count + delete + add logic to the application. You might also want to use expiring columns, but depends on your use case. http://www.datastax.com/dev/blog/whats-new-in-cassandra-0-8-part-2-counters On Mon, Jul 18, 2011 at 3:56 PM, aaron morton <aa...@thelastpickle.com>wrote: > There is no support for a feature like that, and i doubt it would ever be > supported. For one there there are no locks during a write, so it's not > possible to definitively say there are 100 columns at a particular instance > of time. > > You would need to read all columns and delete the ones you no longer need. > > You could also try Redis. > > Cheers > > > ----------------- > Aaron Morton > Freelance Cassandra Developer > @aaronmorton > http://www.thelastpickle.com > > On 19 Jul 2011, at 03:22, JKnight JKnight wrote: > > > Dear all, > > > > I want to keep only 100 column of a key: when I add a column for a key, > if the number column of key is 100, another column (by order) will be > deleted. > > > > Does Cassandra have setting for that? > > > > -- > > Best regards, > > JKnight > >
