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ZooKeeper Bug ZOOKEEPER-2080: ReconfigRecoveryTest fails intermittently

The JUnit test ReconfigRecoveryTest.testCurrentObserverIsParticipantInNewConfig fails intermittently.

The cause of the bug had been unknown for almost 2 years (since 2013).

Using Namazu, we reproduced the bug and analyzed its cause.

The bug has been caused by race conditions in QuorumCnxManager, which manages sockets for leader election.

To fix the bug gracefully, drastic changes to QuorumCnxManager (suggested since 2010: ZOOKEEPER-901) might be needed.

How to Reproduce the Bug with Namazu

The bug can be easily reproduced by injecting several tens of millisecs sleeps to FLE packets.

Start Namazu

Please see ../../doc/how-to-setup-env.md for how to setup the environment.

$ sudo sh -c 'echo 0 > /proc/sys/net/ipv4/tcp_autocorking' # recommended if you are using Linux 3.14 or later
$ sudo useradd -m nfqhooked # this user is needed for internal sandboxing
$ sudo PYTHONPATH=$(pwd)/../../misc ../../bin/nmz init --force config.toml materials /tmp/zk-2080

Disabling tcp_autocorking is recommended for future zktraffic-based inspection support.

Currently zktraffic does not work well with ZOOKEEPER-2080 scenario, because some packets still somehow get corked even when tcp_autocorking is disabled.

Run Experiments

$ sudo PYTHONPATH=$(pwd)/../../misc ../../bin/nmz run /tmp/zk-2080

If the bug could not be reproduced, you might have to modify the interval parameter in config.toml. (about 30 msecs to 80 msecs)

Analyze

Unlike ZOOKEEPER-2212, you cannot use the Namazu event history for analysis.

Instead, you can estimate the cause of the bug using Namazu branch analyzer for Java.

$ java -jar ../../bin/nmz-analyzer.jar /tmp/zk-2080/ --classes-path /tmp/zk-2080/materials/zookeeper/build/classes
[DEBUG] net.osrg.namazu.ExperimentAnalyzer - Scanning /tmp/zk-2080/00000000: experiment successful=false
[DEBUG] net.osrg.namazu.ExperimentAnalyzer - Scanning /tmp/zk-2080/00000001: experiment successful=true
..
Suspicious: org.apache.zookeeper.server.quorum.QuorumCnxManager::connectAll
	- at line 511: branch on success=0, on failure=4
..
Suspicious: org.apache.zookeeper.server.quorum.QuorumCnxManager::receiveConnection
	- at line 358: branch on success=0, on failure=4
..

Environment Variables

  • NMZ_DISABLE(default: (unset)): disable the substantial part of Namazu if set
  • ZK_GIT_COMMIT(default:(see materials/lib.sh)) : use another ZooKeeper version
  • ZK_SOURCE_DIR(default: (unset)) : use another ZooKeeper source directory if set