Hi Patrick,
You are correct, the test restarts both ZooKeeper server and the client. The
client opens a new connection after restarting. So we would expect that the
ephmeral znode (/foo) to expire after the session timeout. However, the
client with the new session creates the ephemeral znode (/foo) again after
it reboots (it sets a watch for /foo and recreates /foo if it is deleted or
doesn't exist). The client is not reusing the session ID. What I expect to
see is that the older /foo should expire after which a new /foo should get
created. Is my expectation correct?
What confuses me is the following output of 3 successive getstat /foo
requests on A (the zxid, time and owner fields). Notice that the older
znode reappeared.
At the same time when I do getstat at B and C, I see the newer /foo.
log4j:WARN No appenders could be found for logger
(org.apache.zookeeper.ZooKeeper).
log4j:WARN Please initialize the log4j system properly.
cZxid = 0x105ef
ctime = Tue Oct 05 15:00:50 UTC 2010
mZxid = 0x105ef
mtime = Tue Oct 05 15:00:50 UTC 2010
pZxid = 0x105ef
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x2b7ce57ce4
dataLength = 54
numChildren = 0
log4j:WARN No appenders could be found for logger
(org.apache.zookeeper.ZooKeeper).
log4j:WARN Please initialize the log4j system properly.
cZxid = 0x10607
ctime = Tue Oct 05 15:01:07 UTC 2010
mZxid = 0x10607
mtime = Tue Oct 05 15:01:07 UTC 2010
pZxid = 0x10607
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x2b7ce5bda4
dataLength = 54
numChildren = 0
log4j:WARN No appenders could be found for logger
(org.apache.zookeeper.ZooKeeper).
log4j:WARN Please initialize the log4j system properly.
cZxid = 0x105ef
ctime = Tue Oct 05 15:00:50 UTC 2010
mZxid = 0x105ef
mtime = Tue Oct 05 15:00:50 UTC 2010
pZxid = 0x105ef
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x2b7ce57ce4
dataLength = 54
numChildren = 0
Thanks for your help.
-Vishal
On Wed, Oct 6, 2010 at 4:45 PM, Patrick Hunt ph...@apache.org wrote:
Vishal the attachment seems to be getting removed by the list daemon (I
don't have it), can you create a JIRA and attach? Also this is a good
question for the ppl on zookeeper-user. (ccing)
You are aware that ephemeral znodes are tied to the session? And that
sessions only expire after the session timeout period? At which time any
znodes created during that session are then deleted. The fact that you are
killing your client process leads me to believe that you are not closing
the session cleanly (meaning that it will eventually expire after the
session timeout period), in which case the ephemeral znodes _should_
reappear when A is restarted and successfully rejoins the cluster. (at
least
until the session timeout is exceeded)
Patrick
On Tue, Oct 5, 2010 at 11:04 AM, Vishal K vishalm...@gmail.com wrote:
Hi,
I have a 3 node ZK cluster (A, B, C). On one of the the nodes (node A), I
have a ZK client running that connects to the local server and creates an
ephemeral znode to indicate clients on other nodes that it is online.
I have test script that reboots the zookeeper server as well as client on
A. The test does a getstat on the ephemeral znode created by the client
on
A. I am seeing that the view of znodes on A is different from the other 2
nodes. I can tell this from the session ID that the client gets after
reconnecting to the local ZK server.
So the test is simple:
- kill zookeeper server and client process
- wait for a few seconds
- do zkCli.sh stat ... test.out
What I am seeing is that the ephemeral znode with old zxid, time, and
session ID is reappearing on node A. I have attached the output of 3
consecutive getstat requests of the test (see client_getstat.out). Notice
that the third output is the same as the first one. That is, the old
ephemeral znode reappeared at A. However, both B and C are showing the
latest znode with correct time, zxid and session ID (output not
attached).
After this point, all following getstat requests on A are showing the old
znode. Whereas, B and C show the correct znode every time the client on A
comes online. This is something very perplexing. Earlier I thought this
was
a bug in my client implementation. But the test shows that the ZK server
on
A after reboot is out of sync with rest of the servers.
The stat command to each server shows that the servers are in sync as far
as zxid's are concerned (see stat.out). So there is something wrong with
A's
local database that is causing this problem.
Has anyone seen this before? I will be doing more debugging in the next
few
days. Comments/suggestions for further debugging are welcomed.
-Vishal
