Re: A question about Watcher

2010-08-17 Thread Patrick Hunt
All servers keep a copy - so you can shutdown the zk service entirely (all servers) and restart it and the sessions are maintained. Patrick On 08/16/2010 06:34 PM, Qian Ye wrote: Thx Mahadev and Benjamin, it seems that I've got some misunderstanding about the client. I will check it out. Anot

Re: A question about Watcher

2010-08-16 Thread Ted Dunning
Almost never. There was a bug a while back that could have conceivably caused that under rare circumstances, but I don't know of any current mechanism for this lossage that you are asking about. On Mon, Aug 16, 2010 at 6:34 PM, Qian Ye wrote: > My question is, if the master failed, does that me

Re: A question about Watcher

2010-08-16 Thread Qian Ye
Thx Mahadev and Benjamin, it seems that I've got some misunderstanding about the client. I will check it out. Another relevant question. I noticed that the master zookeeper server keep a track of all the client session which connects to every zookeeper server in the same cluster. So when a slave z

Re: A question about Watcher

2010-08-16 Thread Benjamin Reed
the client does keep track of the watches that it has outstanding. when it reconnects to a new server it tells the server what it is watching for and the last view of the system that it had. ben On 08/16/2010 09:28 AM, Qian Ye wrote: thx for explaination. Since the watcher can be preserved wh

Re: A question about Watcher

2010-08-16 Thread Mahadev Konar
Hi Qian, The watcher information is saved at the client, and the client will reattach the watches to the new server it connects to. Hope that helps. Thanks mahadev On 8/16/10 9:28 AM, "Qian Ye" wrote: > thx for explaination. Since the watcher can be preserved when the client > switch the zo

Re: A question about Watcher

2010-08-16 Thread Qian Ye
thx for explaination. Since the watcher can be preserved when the client switch the zookeeper server it connects to, does that means all the watchers information will be saved on all the zookeeper servers? I didn't find any source of the client can hold the watchers information. On Tue, Aug 17, 2

Re: A question about Watcher

2010-08-16 Thread Benjamin Reed
good point ted! i should have waited a bit longer before responding :) ben On 08/16/2010 09:20 AM, Ted Dunning wrote: There are two different concepts. One is connection loss. Watchers survive this and the client automatically connects to another member of the ZK cluster. The other is sessio

Re: A question about Watcher

2010-08-16 Thread Ted Dunning
I should correct this. The watchers will deliver a session expiration event, but since the connection is closed at that point no further events will be delivered and the cluster will remove them. This is as good as the watchers disappearing. On Mon, Aug 16, 2010 at 9:20 AM, Ted Dunning wrote:

Re: A question about Watcher

2010-08-16 Thread Benjamin Reed
zookeeper takes care of reregistering all watchers on reconnect. you don't need to do anything. ben On 08/16/2010 09:04 AM, Qian Ye wrote: Hi all: Will the watchers of a client be losed when the client disconnects from a Zookeeper server? It is said at http://hadoop.apache.org/zookeeper/docs/

Re: A question about Watcher

2010-08-16 Thread Ted Dunning
There are two different concepts. One is connection loss. Watchers survive this and the client automatically connects to another member of the ZK cluster. The other is session expiration. Watchers do not survive this. This happens when a client does not provide timely evidence that it is alive

A question about Watcher

2010-08-16 Thread Qian Ye
Hi all: Will the watchers of a client be losed when the client disconnects from a Zookeeper server? It is said at http://hadoop.apache.org/zookeeper/docs/current/zookeeperProgrammers.html#ch_zkWatchesthat " *When a client reconnects, any previously registered watches will be reregistered and trigg