We use ZK for some incrementing counters and this is method that does it (this is wrapped in a Thrift call) :

 public long getNextSequenceId()
    {
      Stat stat = null;
      String path = "/<cluster name>/" +  "/SequenceId";
      try
      {
        stat = zk_.setData( path , new byte[0] , -1);
      }
      catch (InterruptedException ie)
      {
        // handle it.
      }
      catch (KeeperException ke)
      {
        // handle it.
      }
      return stat.getMzxid();
    }


Avinash




On Mon, Mar 29, 2010 at 11:40 AM, Eric Hauser <ewhauser@gmail.com> wrote:
That's good to know.  I've often seen high latency between availability zones.

BTW, does anyone from Digg patrol the list?  I'm really interested in some additional the implementation of atomic counters with ZooKeeper.


On Mon, Mar 29, 2010 at 1:58 PM, Joe Stump <joe@joestump.net> wrote:

On Mar 29, 2010, at 11:55 AM, Eric Hauser wrote:

> Does the information is the below link about Cassandra and replication over WAN have any merit or is it just FUD?

I can attest Cassandra works fine over inter-DC connections. We have ~20 nodes spread across three Amazon "Availability Zones". I know Digg is doing bi-coastal Cassandra as well without issues.

Cassandra was specifically built to work well over WAN / intermittently failing connections / setups.

--Joe