动物园管理员zk_max_latency是如何计算的？

Question

嗨我刚从我的动物园管理员那里取了一些数据..。

如您所见，zk_max_latency相当高。但这是它曾经达到的最大值，还是始终是当前值？

echo mntr | nc localhost 2181
zk_version  3.4.13-2d71af4dbe22557fda74f9a9b4309b15a7487f03, built on 06/29/2018 04:05 GMT
zk_avg_latency  0
zk_max_latency  4738
zk_min_latency  0
zk_packets_received 2387852
zk_packets_sent 2387928
zk_num_alive_connections    29
zk_outstanding_requests 0
zk_server_state follower
zk_znode_count  7973
zk_watch_count  74
zk_ephemerals_count 22
zk_approximate_data_size    12356979
zk_open_file_descriptor_count   62
zk_max_file_descriptor_count    16384
zk_fsync_threshold_exceed_count 2

Answer 1

zk_max|avg|min_latency度量是从ZK服务器启动开始计算的。

mntr命令由MonitorCommand处理，它从ZooKeeperServer.serverStats.requestLatency查询max/avg/min请求指标

ZKDatabase zkdb = zkServer.getZKDatabase();
ServerStats stats = zkServer.serverStats();

print("version", Version.getFullVersion());

print("avg_latency", stats.getAvgLatency());
print("max_latency", stats.getMaxLatency());
print("min_latency", stats.getMinLatency());

ServerStats.java

// getters
public long getMinLatency() {
    return requestLatency.getMin();
}

public double getAvgLatency() {
    return requestLatency.getAvg();
}

public long getMaxLatency() {
    return requestLatency.getMax();
}

请求延迟在ServerStats.updateLatency()上更新。核心实现类是AvgMinMaxCounter。

public void updateLatency(Request request, long currentTime) {
    long latency = currentTime - request.createTime;
    if (latency < 0) {
        return;
    }
    requestLatency.addDataPoint(latency);
    if (request.getHdr() != null) {
        // Only quorum request should have header
        ServerMetrics.UPDATE_LATENCY.add(latency);
    } else {
        // All read request should goes here
        ServerMetrics.READ_LATENCY.add(latency);
    }
}

Answer 2

zk_max_latency：此ZooKeeper服务器以毫秒为单位处理请求的最长时间。

不，这是自上次重新启动ZooKeeper服务器以来测量的。