Re: question about watcher
thanks Patrick, I want to know all watches set by all clients. I would open a jira and write some design think about it later. On Tue, Nov 2, 2010 at 11:53 PM, Patrick Hunt ph...@apache.org wrote: Hi Qian Ye, yes you should open a JIRA for this. If you want to work on a patch we could advise you. One thing not clear to me, are you interested in just the watches set by the particular client, or all watches set by all clients? The first should be relatively easy to get, the second would be more involved (the difference btw getting local watches and having to talk to the server to get all watches). Does this have to be a client api or more administrative in nature? Also see http://hadoop.apache.org/zookeeper/docs/current/zookeeperAdmin.html#sc_zkCommands specifically the wchs,wchp,wchs 4 letter words. Regards, Patrick On Tue, Nov 2, 2010 at 4:11 AM, Qian Ye yeqian@gmail.com wrote: Hi all, Is there any progress about this issue? Should we open a new JIRA for it? We really need a way to know who set watchers on a specific node. thanks~ On Thu, Aug 6, 2009 at 11:01 PM, Qian Ye yeqian@gmail.com wrote: Thanks Mahadev, I think it is a useful feature for many scenarios. On Thu, Aug 6, 2009 at 12:59 PM, Mahadev Konar maha...@yahoo-inc.com wrote: Hi Qian, There isnt any such api. We have been thinking abt adding an api on cancelling a cleints watches. We have been thinking about adding a proc filesystem wherein a cleintt will have a list of all the watches. This data can be used to know which clients are watching what znode, but this has always been in the future discussions for us. We DO NOT have anything planned in the near future for this. Thanks mahadev On 8/5/09 6:57 PM, Qian Ye yeqian@gmail.com wrote: Hi all: Is there a client API for querying the watchers' owner for a specific znode? In some situation, we want to find out who set watchers on the znode. thx -- With Regards! Ye, Qian Made in Zhejiang University -- With Regards! Ye, Qian -- With Regards! Ye, Qian
Re: question about watcher
Definitely checkout the 4letter words then (wch*). Keep in mind getting this data may be expensive (if there's alot of it) and that watches are locak, so servers only know about the watches from sessions est through it (server 1 doesn't know about watches of sessions connected on server 2, 3, etc...). Patrick On Wed, Nov 3, 2010 at 1:13 AM, Qian Ye yeqian@gmail.com wrote: thanks Patrick, I want to know all watches set by all clients. I would open a jira and write some design think about it later. On Tue, Nov 2, 2010 at 11:53 PM, Patrick Hunt ph...@apache.org wrote: Hi Qian Ye, yes you should open a JIRA for this. If you want to work on a patch we could advise you. One thing not clear to me, are you interested in just the watches set by the particular client, or all watches set by all clients? The first should be relatively easy to get, the second would be more involved (the difference btw getting local watches and having to talk to the server to get all watches). Does this have to be a client api or more administrative in nature? Also see http://hadoop.apache.org/zookeeper/docs/current/zookeeperAdmin.html#sc_zkCommands specifically the wchs,wchp,wchs 4 letter words. Regards, Patrick On Tue, Nov 2, 2010 at 4:11 AM, Qian Ye yeqian@gmail.com wrote: Hi all, Is there any progress about this issue? Should we open a new JIRA for it? We really need a way to know who set watchers on a specific node. thanks~ On Thu, Aug 6, 2009 at 11:01 PM, Qian Ye yeqian@gmail.com wrote: Thanks Mahadev, I think it is a useful feature for many scenarios. On Thu, Aug 6, 2009 at 12:59 PM, Mahadev Konar maha...@yahoo-inc.com wrote: Hi Qian, There isnt any such api. We have been thinking abt adding an api on cancelling a cleints watches. We have been thinking about adding a proc filesystem wherein a cleintt will have a list of all the watches. This data can be used to know which clients are watching what znode, but this has always been in the future discussions for us. We DO NOT have anything planned in the near future for this. Thanks mahadev On 8/5/09 6:57 PM, Qian Ye yeqian@gmail.com wrote: Hi all: Is there a client API for querying the watchers' owner for a specific znode? In some situation, we want to find out who set watchers on the znode. thx -- With Regards! Ye, Qian Made in Zhejiang University -- With Regards! Ye, Qian -- With Regards! Ye, Qian
Re: question about watcher
Hi all, Is there any progress about this issue? Should we open a new JIRA for it? We really need a way to know who set watchers on a specific node. thanks~ On Thu, Aug 6, 2009 at 11:01 PM, Qian Ye yeqian@gmail.com wrote: Thanks Mahadev, I think it is a useful feature for many scenarios. On Thu, Aug 6, 2009 at 12:59 PM, Mahadev Konar maha...@yahoo-inc.comwrote: Hi Qian, There isnt any such api. We have been thinking abt adding an api on cancelling a cleints watches. We have been thinking about adding a proc filesystem wherein a cleintt will have a list of all the watches. This data can be used to know which clients are watching what znode, but this has always been in the future discussions for us. We DO NOT have anything planned in the near future for this. Thanks mahadev On 8/5/09 6:57 PM, Qian Ye yeqian@gmail.com wrote: Hi all: Is there a client API for querying the watchers' owner for a specific znode? In some situation, we want to find out who set watchers on the znode. thx -- With Regards! Ye, Qian Made in Zhejiang University -- With Regards! Ye, Qian
Re: question about watcher
Hi Qian Ye, yes you should open a JIRA for this. If you want to work on a patch we could advise you. One thing not clear to me, are you interested in just the watches set by the particular client, or all watches set by all clients? The first should be relatively easy to get, the second would be more involved (the difference btw getting local watches and having to talk to the server to get all watches). Does this have to be a client api or more administrative in nature? Also see http://hadoop.apache.org/zookeeper/docs/current/zookeeperAdmin.html#sc_zkCommands specifically the wchs,wchp,wchs 4 letter words. Regards, Patrick On Tue, Nov 2, 2010 at 4:11 AM, Qian Ye yeqian@gmail.com wrote: Hi all, Is there any progress about this issue? Should we open a new JIRA for it? We really need a way to know who set watchers on a specific node. thanks~ On Thu, Aug 6, 2009 at 11:01 PM, Qian Ye yeqian@gmail.com wrote: Thanks Mahadev, I think it is a useful feature for many scenarios. On Thu, Aug 6, 2009 at 12:59 PM, Mahadev Konar maha...@yahoo-inc.comwrote: Hi Qian, There isnt any such api. We have been thinking abt adding an api on cancelling a cleints watches. We have been thinking about adding a proc filesystem wherein a cleintt will have a list of all the watches. This data can be used to know which clients are watching what znode, but this has always been in the future discussions for us. We DO NOT have anything planned in the near future for this. Thanks mahadev On 8/5/09 6:57 PM, Qian Ye yeqian@gmail.com wrote: Hi all: Is there a client API for querying the watchers' owner for a specific znode? In some situation, we want to find out who set watchers on the znode. thx -- With Regards! Ye, Qian Made in Zhejiang University -- With Regards! Ye, Qian
Re: A question about Watcher
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. 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 zookeeper server failed, the clients it served, can switch to another zookeeper server and keep their old session (the new zookeeper server can get the session information from the master). My question is, if the master failed, does that means some session information will definitely be lost? thx~ On Tue, Aug 17, 2010 at 12:40 AM, Benjamin Reedbr...@yahoo-inc.com wrote: 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 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, 2010 at 12:21 AM, Ted Dunningted.dunn...@gmail.com wrote: 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 Dunningted.dunn...@gmail.com wrote: The other is session expiration. Watchers do not survive this. This happens when a client does not provide timely evidence that it is alive and is marked as having disappeared by the cluster.
A question about Watcher
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 triggered if needed. In general this all occurs transparently.* It means that we need not to do any extra things about watchers if a client disconnected from Zookeeper server A, and reconnect to Zookeeper server B, doesn't it? Or I should reregistered all the watchers if this kind of reconnection happened? thx~ -- With Regards! Ye, Qian
Re: A question about Watcher
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 and is marked as having disappeared by the cluster. On Mon, Aug 16, 2010 at 9:04 AM, Qian Ye yeqian@gmail.com 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/current/zookeeperProgrammers.html#ch_zkWatchesthat *When a client reconnects, any previously registered watches will be reregistered and triggered if needed. In general this all occurs transparently.* It means that we need not to do any extra things about watchers if a client disconnected from Zookeeper server A, and reconnect to Zookeeper server B, doesn't it? Or I should reregistered all the watchers if this kind of reconnection happened? thx~ -- With Regards! Ye, Qian
Re: A question about Watcher
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/current/zookeeperProgrammers.html#ch_zkWatchesthat *When a client reconnects, any previously registered watches will be reregistered and triggered if needed. In general this all occurs transparently.* It means that we need not to do any extra things about watchers if a client disconnected from Zookeeper server A, and reconnect to Zookeeper server B, doesn't it? Or I should reregistered all the watchers if this kind of reconnection happened? thx~
Re: A question about Watcher
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 ted.dunn...@gmail.com wrote: The other is session expiration. Watchers do not survive this. This happens when a client does not provide timely evidence that it is alive and is marked as having disappeared by the cluster.
Re: A question about Watcher
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 session expiration. Watchers do not survive this. This happens when a client does not provide timely evidence that it is alive and is marked as having disappeared by the cluster. On Mon, Aug 16, 2010 at 9:04 AM, Qian Yeyeqian@gmail.com 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/current/zookeeperProgrammers.html#ch_zkWatchesthat *When a client reconnects, any previously registered watches will be reregistered and triggered if needed. In general this all occurs transparently.* It means that we need not to do any extra things about watchers if a client disconnected from Zookeeper server A, and reconnect to Zookeeper server B, doesn't it? Or I should reregistered all the watchers if this kind of reconnection happened? thx~ -- With Regards! Ye, Qian
Re: A question about Watcher
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, 2010 at 12:21 AM, Ted Dunning ted.dunn...@gmail.com wrote: 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 ted.dunn...@gmail.com wrote: The other is session expiration. Watchers do not survive this. This happens when a client does not provide timely evidence that it is alive and is marked as having disappeared by the cluster. -- With Regards! Ye, Qian
Re: A question about Watcher
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 yeqian@gmail.com wrote: 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, 2010 at 12:21 AM, Ted Dunning ted.dunn...@gmail.com wrote: 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 ted.dunn...@gmail.com wrote: The other is session expiration. Watchers do not survive this. This happens when a client does not provide timely evidence that it is alive and is marked as having disappeared by the cluster. -- With Regards! Ye, Qian
Re: A question about Watcher
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 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, 2010 at 12:21 AM, Ted Dunningted.dunn...@gmail.com wrote: 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 Dunningted.dunn...@gmail.com wrote: The other is session expiration. Watchers do not survive this. This happens when a client does not provide timely evidence that it is alive and is marked as having disappeared by the cluster.
Re: A question about Watcher
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 zookeeper server failed, the clients it served, can switch to another zookeeper server and keep their old session (the new zookeeper server can get the session information from the master). My question is, if the master failed, does that means some session information will definitely be lost? thx~ On Tue, Aug 17, 2010 at 12:40 AM, Benjamin Reed br...@yahoo-inc.com wrote: 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 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, 2010 at 12:21 AM, Ted Dunningted.dunn...@gmail.com wrote: 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 Dunningted.dunn...@gmail.com wrote: The other is session expiration. Watchers do not survive this. This happens when a client does not provide timely evidence that it is alive and is marked as having disappeared by the cluster. -- With Regards! Ye, Qian
Re: A question about Watcher
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 yeqian@gmail.com wrote: My question is, if the master failed, does that means some session information will definitely be lost?
Re: question about watcher
Thanks Mahadev, I think it is a useful feature for many scenarios. On Thu, Aug 6, 2009 at 12:59 PM, Mahadev Konar maha...@yahoo-inc.comwrote: Hi Qian, There isnt any such api. We have been thinking abt adding an api on cancelling a cleints watches. We have been thinking about adding a proc filesystem wherein a cleintt will have a list of all the watches. This data can be used to know which clients are watching what znode, but this has always been in the future discussions for us. We DO NOT have anything planned in the near future for this. Thanks mahadev On 8/5/09 6:57 PM, Qian Ye yeqian@gmail.com wrote: Hi all: Is there a client API for querying the watchers' owner for a specific znode? In some situation, we want to find out who set watchers on the znode. thx -- With Regards! Ye, Qian Made in Zhejiang University
Re: question about watcher
Hi Qian, There isnt any such api. We have been thinking abt adding an api on cancelling a cleints watches. We have been thinking about adding a proc filesystem wherein a cleintt will have a list of all the watches. This data can be used to know which clients are watching what znode, but this has always been in the future discussions for us. We DO NOT have anything planned in the near future for this. Thanks mahadev On 8/5/09 6:57 PM, Qian Ye yeqian@gmail.com wrote: Hi all: Is there a client API for querying the watchers' owner for a specific znode? In some situation, we want to find out who set watchers on the znode. thx
