it is possible for the time to pass without the session expiring. Imagine a session timeout of 15 seconds. there is correlated power outage affecting the zookeeper servers. lets say it takes 5 minutes to recover power and reboot. when the service recovers, it resets expiration times, so when the servers start back up and the client reconnects (assuming it is retrying every few seconds), the session will be recovered and everything will proceed as normal. if the client library generates a session expired, the client could connect with a new session after the service recovers and see its own ephemeral nodes for 15 seconds.
ben ________________________________________ From: Nitay [nit...@gmail.com] Sent: Thursday, March 26, 2009 12:09 PM To: firstname.lastname@example.org Subject: Re: Semantics of ConnectionLoss exception Why is it done that way? How am I supposed to reliably detect that my ephemeral nodes are gone? Why not deliver the Session Expired event on the client side after the right time has passed without communication to any server? On Thu, Mar 26, 2009 at 10:58 AM, Mahadev Konar <maha...@yahoo-inc.com>wrote: > > > > Isn't it the case that the client won't get session expired until it's > > able to connect to a server, right? So what might happen is that the > > client loses connection to the server, the server eventually expires the > > client and deletes ephemerals (notifying all watchers) but the client > > won't see the "session expiration" until it is able to reconnect to one > > of the servers. ie the client doesn't know it's been expired until it's > > able to reconnect to the cluster, at which point it's notified that it's > > been expired. > You are right pat! > > mahadev > > > > >> > http://hadoop.apache.org/zookeeper/docs/r3.0.1/zookeeperProgrammers.html > >> Has this information scattered around, but we should put it in the FAQ > >> specifically. > > > > 3.0.1 is a bit old, try this for the latest docs: > > > http://hadoop.apache.org/zookeeper/docs/current/zookeeperProgrammers.html > > > >> - Is the ZooKeeper handle I'm using dead after this event? > >> Again no. your handle is valid until you get an session expiry event or > you > >> do a zoo_close on your handle. > >> > >> > >> Thanks > >> mahadev > >> > >> > >> > >> > >> On 3/25/09 5:42 PM, "Nitay" <nit...@gmail.com> wrote: > >> > >>> I'm a little unclear about the ConnectionLoss exception as it's > described in > >>> the FAQ and would like some clarification. > >>> > >>> From the state diagram, http://wiki.apache.org/hadoop/ZooKeeper/FAQ#1, > there > >>> are three events that cause a ConnectionLoss: > >>> > >>> 1) In Connecting state, call close(). > >>> 2) In Connected state, call close(). > >>> 3) In Connected state, get disconnected. > >>> > >>> It's the third one I'm unclear about. > >>> > >>> - Does this event happening mean my ephemeral nodes will go away? > >>> - Is the ZooKeeper handle I'm using dead after this event? Meaning > that, > >>> similar to the SessionExpired case, I need to construct a new > connection > >>> handle to ZooKeeper and take care of the restarting myself. It seems > from > >>> the diagram that this should not be the case. Rather, seeing as the > >>> disconnected event sends the user back to the Connecting state, my > handle > >>> should be fine and the library will keep trying to reconnect to > ZooKeeper > >>> internally? I understand my current operation may have failed, what I'm > >>> asking about is future operations. > >>> > >>> Thanks, > >>> -n > >> > >