[ZOOKEEPER-2774] Ephemeral znode will not be removed when sesstion timeout, if the system time of ZooKeeper node changes unexpectedly.

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.4.8, 3.4.9, 3.4.10
• Fix Version/s: 3.4.11
• Component/s: server

Environment

Centos6.5

• Assignee: Jiafu Jiang
• Reporter: Jiafu Jiang
• Created: 04/May/17 02:28
• Updated: 13/Jul/17 02:59
• Resolved: 18/May/17 21:31

Description

1. Deploy a ZooKeeper cluster with one node.
2. Create a Ephemeral znode.
3. Change the system time of the ZooKeeper node to a earlier point.
4. Disconnect the client with the ZooKeeper server.

Then the ephemeral znode will exist for a long time even when session timeout.

I have read the ZooKeeper source code and I find the code int SessionTrackerImpl.java，

SessionTrackerImpl.java

    @Override
    synchronized public void run() {
        try {
            while (running) {
                currentTime = System.currentTimeMillis();
                if (nextExpirationTime > currentTime) {
                    this.wait(nextExpirationTime - currentTime);
                    continue;
                }
                SessionSet set;
                set = sessionSets.remove(nextExpirationTime);
                if (set != null) {
                    for (SessionImpl s : set.sessions) {
                        setSessionClosing(s.sessionId);
                        expirer.expire(s);
                    }
                }
                nextExpirationTime += expirationInterval;
            }
        } catch (InterruptedException e) {
            handleException(this.getName(), e);
        }
        LOG.info("SessionTrackerImpl exited loop!");
    }

I think it may be better to use System.nanoTime(), not System.currentTimeMillis, because the later can be changed manually or automatically by a NTP client.

Issue Links

• requires: ZOOKEEPER-1366 Zookeeper should be tolerant of clock adjustments
• links to: GitHub Pull Request #253