My very shaky understanding from skimming those issues was that in some
cases there were two threads handling different types of data that are
related to the same transaction -- but maybe that's only true when
there's a leader and a follower. But I also saw something in there
about restoring data from a snapshot vs. restoring it from a log, which
seems like it could have happened in a single node case.
In any case, now the 3.3.3 is out I'll give it a try and report back if
we keep seeing this.
Thanks!
Jeremy
On 03/01/2011 02:59 PM, Vishal Kher wrote:
Hi Jeremy,
I just realized that you are using a standalone ZK server. I don't
think the bugs apply to you, so I don't have an answer to your question.
I think 3.3.3 should be released soon:
http://zookeeper-dev.578911.n2.nabble.com/VOTE-Release-ZooKeeper-3-3-3-candidate-1-td6059109.html
-Vishal
On Tue, Mar 1, 2011 at 4:15 PM, Jeremy Stribling <[email protected]
<mailto:[email protected]>> wrote:
Thanks for the pointers Vishal, I hadn't seen those. They look
like they could be related, but without knowing how metadata
updates are grouped into transactions, it's hard for me to say. I
would expect the cversion update to happen within the same
transaction as the creation of a new child, but if they get
written to the log in two separate steps, perhaps these issues
could explain it.
Any estimate on when 3.3.3 will be released? I haven't seen any
updates on the user list about it. Thanks,
Jeremy
On 03/01/2011 12:40 PM, Vishal Kher wrote:
Hi Jermy,
One of the main reasons for 3.3.3 release was to include fixes
for znode
inconsistency bugs.
Have you taken a look at
https://issues.apache.org/jira/browse/ZOOKEEPER-962and
https://issues.apache.org/jira/browse/ZOOKEEPER-919?
The problem that you are seeing sounds similar to the ones
reported.
-Vishal
On Mon, Feb 28, 2011 at 8:04 PM, Jeremy
Stribling<[email protected] <mailto:[email protected]>> wrote:
Hi all,
A while back I noticed that my Zookeeper cluster got into
a state where I
would get a "node exists" error back when creating a
sequential znode -- see
the thread starting at
http://mail-archives.apache.org/mod_mbox/hadoop-zookeeper-user/201010.mbox/%[email protected]%3Efor
more details. The summary is that at the time, my
application had a bug
that could have been improperly bringing new nodes into a
cluster.
However, I've seen this a couple more times since fixing
that original bug.
I don't yet know how to reproduce it, but I am going to
keep trying. In
one case, we restarted a node (in a one-node cluster), and
when it came back
up we could no longer create sequential nodes on a certain
parent node, with
a node exists (-110) error code. The biggest child it saw
on restart was
/zkrsm/000000000000002d_record0000120804 (i.e., a sequence
number of
120804), however a stat on the parent node revealed that
the cversion was
only 120710:
[zk:<ip:port>(CONNECTED) 3] stat /zkrsm
cZxid = 0x5
ctime = Mon Jan 17 18:28:19 PST 2011
mZxid = 0x5
mtime = Mon Jan 17 18:28:19 PST 2011
pZxid = 0x1d819
cversion = 120710
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 0
numChildren = 2955
So my question is: how is znode metadata persisted with
respect to the
actual znodes? Is it possible that a node's children will
get synced to
disk before its own metadata, and if it crashes at a bad
time, the metadata
updates will be lost? If so, is there any way to
constrain Zookeeper so
that it will sync its metadata before returning success
for write
operations?
(I'm using Zookeeper 3.3.2 on a Debian Squeeze 64-bit box,
with
openjdk-6-jre 6b18-1.8.3-2.)
I'd be happy to create a JIRA for this if that seems
useful, but without a
way to reproduce it I'm not sure that it is.
Thanks,
Jeremy
