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From Ivan Kelly <iv...@apache.org>
Subject Re: zookeeper max no of children of znode
Date Sat, 27 Jun 2015 10:47:19 GMT
Hi Shushant

Is there any max number of children limit of a znode?
> As there is a limit of 1MB data of a znode.
>
There's no explicit limit to the number of children. However, there is a
limit to the size of the packet that can be sent back from the server in
response to getChildren which effectly ends up being the limit. This is
controls with a system property, jute.maxbuffer and defaults to 4MB (I
think you can get a around 200,000 znodes into this, though it also depends
on the length of the znode name).


> Does in zookeeper noodes which are behind the leader not accept the
> connection til they come in sync? If yes and only those nodes which are in
> sync with leader accept the connection then How Zookeeper is eventual
> consistent, it should be fully consistent then since client will never get
> connected to unsync nodes.
>
Once they have joined the quorum, all zookeeper nodes will accept client
connections. Followers are not guaranteed to be 100% in sync with the
leader, due to physics (messages take time to travel over the network).
However, a follower does guarantee that all clients connected will see all
updates in the same sequence that they occur on the server, and they should
only be a number of milliseconds behind. This isn't eventual consistency.
Thats what databases like cassandra do where all clients will eventually be
able to see all updates though the order it sees them can change.
ZooKeeper provides sequential consistency. However it only provides this
consistency within a single client session.

-Ivan

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