Hi, Sequential Order Guarantee: ---------------------------
Server view:- It will process the requests in sequential fashion. Say, there are two clients connected with the server, client-1 and client-2. Assume application had created a znode /myapp and there is a logic to do distributed locking mechanism. Now both these clients will try to acquire lock by creating '/myapp/lock' znode. I'm calling these requests as request-1(create /myapp/lock) and request-2(create /myapp/lock). Again assume, server receives the requests in the order of request-2 and then request-1. For simplicity, you can imagine there is a Queue maintained at the server and all these requests will be put into this Queue and executes in FIFO order. First, server will pick request-2 and creates /myapp/lock znode. Also, it will send watcher notifications if anyone has registered. Then move on to the next request-2(create /myapp/lock), while executing this will throw exception saying NodeExistsException. ZooKeeper maintains global ordering but how? - Every write is assigned a globally unique id, sequentially ordered identifier called a zxid, or ZooKeeper transaction id. This guarantees a global order to all updates in a ZooKeeper ensemble. Regards, Rakesh -----Original Message----- From: [email protected] [mailto:[email protected]] Sent: 23 October 2014 08:46 To: user Subject: A question about sequential order consistency that zookeeper garantees Hi,Zookeepers, I'd like to ask a question about sequential order consistency that zookeeper garantees. Say, 2 zookeeper clients want to update the same znode data one after the other.Client1 sends the request 1 second before Client2. What would be the end result? There is no order gurantee here, dure to network delay, it is likely that clients1 send the request before client2, but the zookeeper servers first execute the request from Client1 before client2 If this is not what sequential order consistency means, then what exactly does sequential order consistencymeans, what does zookeeper exactly garantee? Thanks. [email protected]
