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  1. ZooKeeper
  2. ZOOKEEPER-1319

Missing data after restarting+expanding a cluster



    • Bug
    • Status: Closed
    • Blocker
    • Resolution: Fixed
    • 3.4.0
    • 3.4.1, 3.5.0
    • None
    • Linux (Debian Squeeze)

    • Reviewed


      I've been trying to update to ZK 3.4.0 and have had some issues where some data become inaccessible after adding a node to a cluster. My use case is a bit strange (as explained before on this list) in that I try to grow the cluster dynamically by having an external program automatically restart Zookeeper servers in a controlled way whenever the list of participating ZK servers needs to change. This used to work just fine in 3.3.3 (and before), so this represents a regression.

      The scenario I see is this:

      1) Start up a 1-server ZK cluster (the server has ZK ID 0).
      2) A client connects to the server, and makes a bunch of znodes, in particular a znode called "/membership".
      3) Shut down the cluster.
      4) Bring up a 2-server ZK cluster, including the original server 0 with its existing data, and a new server with ZK ID 1.
      5) Node 0 has the highest zxid and is elected leader.
      6) A client connecting to server 1 tries to "get /membership" and gets back a -101 error code (no such znode).
      7) The same client then tries to "create /membership" and gets back a -110 error code (znode already exists).
      8) Clients connecting to server 0 can successfully "get /membership".

      I will attach a tarball with debug logs for both servers, annotating where steps #1 and #4 happen. You can see that the election involves a proposal for zxid 110 from server 0, but immediately following the election server 1 has these lines:

      2011-12-05 17:18:48,308 9299 [QuorumPeer[myid=1]/] WARN org.apache.zookeeper.server.quorum.Learner - Got zxid 0x100000001 expected 0x1
      2011-12-05 17:18:48,313 9304 [SyncThread:1] INFO org.apache.zookeeper.server.persistence.FileTxnLog - Creating new log file: log.100000001

      Perhaps that's not relevant, but it struck me as odd. At the end of server 1's log you can see a repeated cycle of getData->create->getData as the client tries to make sense of the inconsistent responses.

      The other piece of information is that if I try to use the on-disk directories for either of the servers to start a new one-node ZK cluster, all the data are accessible.

      I haven't tried writing a program outside of my application to reproduce this, but I can do it very easily with some of my app's tests if anyone needs more information.


        1. logs.tgz
          90 kB
          Jeremy Stribling
        2. ZOOKEEPER-1319_trunk.patch
          8 kB
          Patrick D. Hunt
        3. ZOOKEEPER-1319_trunk2.patch
          8 kB
          Benjamin Reed
        4. ZOOKEEPER-1319.patch
          9 kB
          Patrick D. Hunt
        5. ZOOKEEPER-1319.patch
          9 kB
          Patrick D. Hunt



            phunt Patrick D. Hunt
            strib Jeremy Stribling
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