What version are you on ? 

 but we are finding a secondary index is performing slow 
Not sure what you mean here. 

Are secondary indexes concurrent or single threaded?
Rebuilding a secondary index (via node tool) is a single threaded operation, but *all* indexes specified on the command line are built at the same time. Rebuilding any one index requires reading all the rows in the CF.

Cheers

-----------------
Aaron Morton
Freelance Cassandra Developer
New Zealand

@aaronmorton

On 23/11/2012, at 8:20 AM, Simon Guindon <simon.guindon@jsitelecom.com> wrote:

We are importing data from one column family into a second column family via “nodetool refresh” but we are finding a secondary index is performing slow and the machine CPU is pretty much idle. We are trying to bulk load data as fast as possible.
 
Are secondary indexes concurrent or single threaded?