Not in the same sense as an SQL database. You can freely add columns and rows, just not Column Families or Keyspaces. This is because a KS+CF combo is stored in it's own file, in a certain order, so that it can be efficiently traversed using natural ordering. If you don't have this need and just need a flat K/V database, you can use a single KS+CF for everything.
Comments
"Cassandra requires all nodes to be restarted to apply a schema change, which can be quite a big deal."
That's no longer true. In 0.7, keyspaces and column families may be created, altered, or dropped live.
I thought it might have been fixed by now.
Anyway, you still need a schema with Cassandra.
Not in the same sense as an SQL database. You can freely add columns and rows, just not Column Families or Keyspaces. This is because a KS+CF combo is stored in it's own file, in a certain order, so that it can be efficiently traversed using natural ordering. If you don't have this need and just need a flat K/V database, you can use a single KS+CF for everything.