The disk state should be the authoritative state of a server, so if I remember correctly, we load the database as a way of validating the disk state. I don't claim that this is strictly necessary, but if we are to change it, then I would need to think this through.
About leader election, if a leader loses support from a quorum of followers, then it will drop leadership. Any event that causes a follower to stop receiving messages from the leader or the follower to disconnect from the leader will make it stop supporting the current leader. -Flavio -----Original Message----- From: Sergey Maslyakov [mailto:[email protected]] Sent: 16 July 2013 16:16 To: [email protected] Subject: Re: Maximum size of a snapshot And another extension on top of Kishore's question: do the reelections happen if the previously elected leader remains in the cluster? In other words, what events can trigger re-election and the corresponding temporary degradation of the service provided by Zookeeper? Thank you, /Sergey On Tue, Jul 16, 2013 at 2:21 AM, kishore g <[email protected]> wrote: > Regarding #2. Is that really true that during leader election every > machine reloads snapshot data from disk? Any reason why this is needed > unless it really needs to truncate or undo conflicting transactions already applied? > > > On Mon, Jul 15, 2013 at 9:50 PM, Thawan Kooburat <[email protected]> wrote: > > > Max snapshot size: > > > > Here is my take on these issue, others feel free to add or correct. > > > > 1. Depends on how much RAM your machine has. Snapshot is should be > > less than the available RAM since everything is loaded into memory. > > 2. Depends on what is the availability guarantee that the client needs. > > If there is leader election, every machine need to reload the data > > from disk. So the quorum will be down for at least the same as > > snapshot > loading > > time. The session timeout on the client side should be at least > > longer than expected downtime during leader election. > > > > -- > > Thawan Kooburat > > > > > > > > > > > > On 7/15/13 8:46 PM, "Sergey Maslyakov" <[email protected]> wrote: > > > > >I have a couple of sizing questions to the users and developers. > > >Hope, > you > > >don't mind answering those. > > > > > >What is the guideline for the maximum reasonable size of a DataTree > that a > > >single ZK server can manage? If ZK server writes out a snapshot of > > >about 1GB in size, is it pushed beyond the limits or is it still manageable? > If > > >so, where is the critical threshold when ZK is really being abused? > > > > > >Similarly, how can I estimate the propagation delay of a change > > >across > an > > >ensemble of three ZK servers? > > > > > > > > >Thank you, > > >/Sergey > > > > >
