Mattias,
Is it possible that after you get NODEEXISTS from creation and before
you do the second getData(), you reconnect to another ZooKeeper
instance? If so, maybe the new connection is to a follower that has not
yet seen the creation. If this is what is happening, then a sync() after
the second NONODE with a third getData() should work. By only doing the
sync() when you hit the unusual race condition it will have no
performance impact.
Bill
On 8/23/2012 8:21 AM, Mattias Persson wrote:
Hi David,
There is nowhere in the code where that node gets deleted. If we refrain
from that suspicion, could there be something else?
2012/8/23 David Nickerson <[email protected]>
It's a little difficult to guess what your application is doing, but it
sounds like there's "someone else" who can create and delete the nodes
you're trying to work with. So when you create the node and check its data,
someone else might have deleted it before you got the chance to check the
data. The same is true when you check that it exists and then check the
data. You could ensure that the node won't be deleted by using ACLs or
giving the node a sequential ephemeral child.
On Thu, Aug 23, 2012 at 6:30 AM, Mattias Persson
<[email protected]>wrote:
Hi,
I've got a problem that I've seen at only a few occasions and which
confuses me a bit. Basically I construct a ZooKeeper client (I'm running
version 3.3.2) where there's a ZK quorum of size 3 running. I get a
SyncConnected event in a Watcher of mine and in that watcher I do a
get-or-create(-if-absent) behaviour where I first do a:
zooKeeper.getData( myPath, false, null );
if that produces a NONODE code I'll try to create it with:
zooKeeper.create( myPath, smallByteArray, OPEN_ACL_UNSAFE, PERSISTENT
);
If that fails with NODEEXISTS code I'll just get it, assuming someone
else
made it before me. What I see from this getData call that I do after
getting this NODEEXISTS code, which is the same as the first one btw, is
that I'll get a NONODE code back. Given in this scenario is that I'm 100%
certain that this node exists in the quorum at myPath in the first place
even.
Questions:
1) How can this happen?
2) Do I use ZooKeeper here in an improper way?
3) Will a later version fix any potential issue I might have hit?
4) What's the guarantees around the state of my ZooKeeper instance after
a
receive a SyncConnected event, is it fully synced with the master at that
point, or will a call to sync() be necessary first?
Best,
Mattias
--
Mattias Persson, [[email protected]]
Hacker, Neo Technology
www.neotechnology.com
