CQL3 change primary key

Question

Suppose I have a table of the following composition.

CREATE TABLE rollup (
  hashname text,
  key text,
  day timestamp,
  counter_value counter,
  PRIMARY KEY (hashname, key, day)
) WITH
...

I want to run a query that looks like

SELECT * FROM rollup WHERE hashname='some_namespaced_hash' AND day>='2013-07-15' AND day<='2013-07-25';

However, this doesn't work because (I think) the following is also relevant to >,<, etc.

Composite keys means it now makes sense for CQL to sport the ORDER BY syntax in SELECT queries as well, but it’s still not nearly as flexible as you might be used to, doing ad-hoc queries in SQL. ORDER BY clauses can only select a single column, and that column has to be the second column in a composite PRIMARY KEY. This holds even for tables with more than 2 column components in the primary key

and here, day is the third column in the primary column key. The only way I can figure to do this is to change the primary compound key to PRIMARY KEY (hashname, day, key). I can't find any documentation that tells me how to do this. Is it possible?

Alternatively, am I missing the "correct" way to solve this problem/am I misinterpreting the problem?

Answer 1

You are right, the only way is switch the order of your primary key. The reason is that, currently, your keys are in this order:

hashname1 key1 day1: counter_value111
hashname1 key1 day2: counter_value112
hashname1 key2 day1: counter_value121
hashname1 key2 day2: counter_value122
hashname1 key3 day1: counter_value131
hashname1 key3 day2: counter_value132

so to retrieve a range of days, Cassandra would need to 'skip' for each key. This is inefficient and not supported. You need to have them in this order:

hashname1 day1 key1: counter_value111
hashname1 day1 key2: counter_value121
hashname1 day1 key3: counter_value131
hashname1 day2 key1: counter_value112
hashname1 day2 key2: counter_value122
hashname1 day2 key3: counter_value132

Unfortunately the only way to do this is to rewrite all your data, and there is no inbuilt way of doing this in Cassandra. You could write a script to do this by reading in the data from one CF, switching round the order, then write out to a new CF and switch. If this needs to be done live it's harder but still possible.