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From 박영근(Alex) <alex.p...@nexr.com>
Subject NodeExistsException when creating a znode with sequential and ephemeral mode
Date Tue, 30 Aug 2011 01:50:38 GMT
Hi, all

I met a problem of NodeExistsException when creating a znode with sequential
and ephemeral mode.
the number of total test was 6442314 and 797 errors had occurred.

The related log message is as in the following:
2011-08-27 16:26:17,559 - INFO  [ProcessThread:-1:PrepRequestProcessor@407][]
- Got user-level KeeperException when processing sessionid:0x2320911802a0002
type:create cxid:0x1246d7 zxid:0xfffffffffffffffe txntype:unknown
reqpath:n/a Error
Path:/NexR/MasteElection/__rwLock/readLock-lssm07-0005967078
Error:KeeperErrorCode = NodeExists for
/NexR/MasteElection/__rwLock/readLock-lssm07-0005967078

The sequential number would be created by increasing parent's Cversion in
the PrepRequestProcess.
So, I guess that this problem was caused by inconsistency of parent znode.

Our test scenario is very aggressive:
The grinder agent sends a request of creating a znode of
CreateMode. SEQUENTIAL_EPHEMERAL.
three number of servers compose ensemble.
each NIC of server is down and up repeatedly;
NIC of server1 become down every one minute and sleeping for 9 seconds, then
up
NIC of server2 become down every 2 minute and sleeping for 9 seconds, then
up
NIC of server3 become down every 3 minute and sleeping for 9 seconds, then
up

while the probability of error occurrence is 0.0001 as mentioned above,
if the ZooKeeper cannot guarantee the consistency, it is  a fatal.

Is there any idea or related issue?

thanks in advance.

alex.

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