Zookeeper错过了连续更改中的事件 [英] Zookeeper missed events on successive changes

问题描述

我目前有一个带有单个Zookeeper节点和Curator的设置来访问数据.读取数据是通过Curator TreeCache完成的.

I currently have a setup with a single zookeeper node and Curator to access the data. Reading data is done through a Curator TreeCache.

我进行了以下测试:

public void test_callback_successive_changes_success_global_new_version() throws InterruptedException {

    ZookeeperTestsHelper.createNewNodeInZookeeperSingleCommand("/my/path/new_node", "some string4", curator);
    ZookeeperTestsHelper.createNewNodeInZookeeperSingleCommand("/my/path/new_node", "some string5", curator);

    Thread.sleep(1000);
    assertThat(<check what events the listener heard>);
}

请注意，执行测试之前"new_node"不存在.

Note that "new_node" does not exists before the test is executed.

    public static void createNewNodeInZookeeperSingleCommand(final String fullPathOfValueInZookeeper, final String valueToSet, final CuratorFramework curator) {
    try {
        if (curator.checkExists().forPath(fullPathOfValueInZookeeper) != null) {
            System.out.println("E: " + valueToSet);
            //Node already exists just set it
            curator.setData().forPath(fullPathOfValueInZookeeper, valueToSet.getBytes());
        } else {
            System.out.println("N: " + valueToSet);
            //Node needs to be created
            curator.create().creatingParentsIfNeeded().forPath(fullPathOfValueInZookeeper, valueToSet.getBytes());
        }
    } catch (Exception e) {
        throw new IllegalStateException("Error", e);
    }
}

我期望缓存侦听器将首先听到添加了某些字符串4"的节点的事件，然后听到了另外发生了由某些字符串5"更新的节点的事件.

I'm expecting that the cache listener will first heard the event of a node added with "some string 4" and then heard another event of node updated with "some string 5".

相反，我只收到添加了值"some string 5"的节点的事件

Instead I am only receiving the event for a node added with value "some string 5"

查看日志，两个命令都正在执行.即记录"N:某些字符串4"和"E:某些字符串5".而且Zookeeper中的最终值是正确的(一些字符串5")，但是我不明白为什么馆长缓存只看到一个事件?

Looking at the logs both commands are being executed. i.e. "N: some string 4" and "E: some string 5" are both logged. And the final value in Zookeeper is correct ("some string 5") but I do not understand why the Curator cache is only seeing a single event?

推荐答案

ZooKeeper(或馆长的TreeCache)不保证您不会错过连续更改的事件.保证是您不会看到与其他客户看到的顺序不同的连续更改.

ZooKeeper (or Curator's TreeCache) don't guarantee that you will not miss events on successive changes. The guarantee is that you won't see successive changes in a different order from what other clients would see.

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