This is because writes are appends to the commit log, which is stored on disk, not memory. The commit log is then flushed to the memtable (in memory), before being written to an sstable on disk.

So, most of the actions in sending out a write are writing to disk.

Also see: http://www.datastax.com/docs/1.2/dml/about_writes


On Fri, Jul 19, 2013 at 1:05 PM, Kanwar Sangha <kanwar@mavenir.com> wrote:

“Insert-heavy workloads will actually be CPU-bound in Cassandra before being memory-bound”


Can someone explain why the internals of why writes are CPU bound ?