zookeeper编程（二）
两年前写过ZooKeeper编程(一)，那时候还在实习。近期组内做了个zookeeper编程的分享，就又把各种问题整理了一下。以下只是简单地copy了幻灯片中的内容，写得不够连贯，读者见谅。
ZooKeeper的轮廓
/---root
|
\----child1
|
\----child2
|
\----child3
|
\----grandson1
|
\----grandson2
采用了简化的praxos算法来确保zookeeper集群节点的数据一致性
只要Quorum的成员有一半以上处于正常状态，就能对外提供服务
任何修改命令都需要leader协调。 在leader的协调过程中，需要3次leader与Follower之间的来回请求响应。并且在此过程中还会涉及事务日志的记录，更糟糕的情况是还有take snapshot的操作。因此此过程可能比较耗时。但Zookeeper的通信中最大特点是异步的，如果请求是连续不断的,Zookeeper的处理是集中处理逻辑，然后批量发送，批量的大小也是有控制的。如果请求量不大，则即刻发送。这样当负载很大时也能保证很大的吞吐量，时效性也在一定程度上进行了保证。
Zookeeper特性
▪简单：本质上是一个小型分布式文件系统，其数据结构就是znode树，对znode的读写是原子的。尽量保证单个znode在1MB一下，通常几K。
▪可靠：可以运行在一组服务器上，数据在每台server上都有备份，避免单点失效。
▪快速：数据全部加载到内存中，读写比例为10:1时性能最佳（读是局部性的，写需要由leader通知给所有server）。在更新内存中的znode之前会先序列到磁盘，服务重启后数据可以恢复。
▪松耦合：Watcher机制使得各客户端与服务器的交互变得松耦合，每个客户端无需知晓其他客户端的存在，就可以和其他客户端进行数据交互。
服务端配置
# 心跳间隔时间
tickTime=2000
# 最小SessionTimeou
minSessionTimeout=4000
# 最大SessionTimeou
maxSessionTimeout=100000
# 允许 follower （相对于 leader 而言的“客户端”）连接并同步到 leader 的初始化连接时间为tickTime的多少倍，超过这个时间则连接失败
initLimit=10
# eader 与 follower 之间发送消息，请求和应答时间长度。如果 follower 在设置的时间内不能与 leader 进行通信，那么此 follower 将被丢弃
syncLimit=5
# 客户端连接最大数
maxClientCnxns=30
客户端配置
ZooKeeper zkp = new ZooKeeper("192.168.119.96:2181, 192.168.119.97:2181 , 192.168.119.98:2181 /app/learn", TIMEOUT,null));
▪client连接zookeeper连接的时候，最好指定>=2个zookeeper服务器地址,这样当一个zookeeper当掉后，client会自动failover到其它的连接。这时候default watcher会先收到一个Disconnected事件，连接的新的Zookeeper服务器后会收到一个SyncConnected事件。这种情况下session建立的临时节点不会丢失，所以程序一般不需要对这点做什么特别的工作。
▪如果你指定的zookeeper中有leader,它好像会直接连接到leader，如果是global集群或多机房集群，建议只指定本机房的zooleeper。
▪如果client连接指定的所有zookeeper server都当掉了，先还是会收到一个Disconnected事件，然后临时节点消失，启动zookeeper server后会收到Expired事件。
import java.io.IOException;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.data.Stat;
/**
*
* @description ZooKeeper基本读写操作演示类
* @author zhangchaoyang
* @date 2014-6-22
*/
public class SimplestDemo {
private static final int TIMEOUT = 3000;
public static void main(String[] args) throws IOException, KeeperException,
InterruptedException {
// Client向zookeeper发送连接请求
ZooKeeper zkp = new ZooKeeper("192.168.119.96:2181/app/learn", // 指定zookeeper
// server的IP、端口列表（当client连接不上server时会按照此列表尝试连接下一台server），以及默认的根目录
TIMEOUT,// Session Timeout
null// 是否设置监听器
);
zkp.create("/znodename", // 节点名称
"znodedata".getBytes(), // 节点上的数据
Ids.OPEN_ACL_UNSAFE,// ACL
CreateMode.EPHEMERAL// 节点类型，有三种：PERSISTENT、EPHEMERAL、SEQUENTIAL。EPHEMERAL节点不允许有子节点
);
Stat stat = zkp.exists("/znodename",// 节点名，如果节点不存在，则exists()返回null
false// 是否设置监听器
);
if (zkp.exists("/znodename", false) != null) {
System.out.println("znodename exists now.");
}
// 修改节点上存储的数据，需要提供version，version设为-1表示强制修改
zkp.setData("/znodename", "newdata".getBytes(), stat.getVersion());
// 读取节点上的数据
String data = new String(zkp.getData("/znodename", false, stat));
System.out.println(data);
// client端主动断开连接
zkp.close();
}
}
Session
▪Zookeeper为每个client分配一个Session，Session数据在每台zookeeper节点上都有备份。
▪Server每隔tickTime向Client发送一个心跳。
▪session失效有两种可能性：client主动调用close() ；Server和Client 长时间（时间大于TIMEOUT ）失去联系。
▪Session失效后与Session关联的数据（比如EPHEMERAL节点，Watcher）会从内存中移除。
▪如果Server和Client只是短暂（时间小于TIMEOUT ）地失去联系，则Session不会失效，Client再次请求Zookeeper时会把上次的SessionID带上。
▪Server和Client失去联系有两种情况：Server宕机（Zookeeper集群会让Client与另一台Server建立连接）；网络异常。
import java.io.IOException;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.KeeperException.ConnectionLossException;
import org.apache.zookeeper.KeeperException.SessionExpiredException;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.data.Stat;
import org.apache.zookeeper.ZooKeeper;
/**
*
* @description Zookeeper Session演示类
* @author zhangchaoyang
* @date 2014-6-22
*/
public class SessionDemo {
/**
* zoo.cfg中的配置：
*
* <pre>
* tickTime=2000
* minSessionTimeout=4000（至少是tickTime的2倍）
* maxSessionTimeout=40000（最大是tickTime的20倍）
* </pre>
*
* 如果客户端建立连接时指定的TIMEOUT不在[minSessionTimeout,maxSessionTimeout]区间内，
* 服务端会强制把它修改到该区间内
*/
private static final int TIMEOUT = 40000; // Session
// Timeout设为40秒，因为心跳周期为2秒，所以如果server向client连续发送20个心跳都收不到回应，则Session过期失效
private static ZooKeeper zkp = null;
private static void connect() throws IOException {
zkp = new ZooKeeper("192.168.119.96:2181/app/learn", TIMEOUT, null);
}
private static void createNode() throws KeeperException,
InterruptedException {
if (zkp != null) {
zkp.create("/znodename", "znodedata".getBytes(),
Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
}
}
private static String getData() throws KeeperException,
InterruptedException {
if (zkp != null) {
Stat stat = zkp.exists("/znodename", false);
return new String(zkp.getData("/znodename", false, stat));
}
return null;
}
private static void disconnect() throws InterruptedException {
if (zkp != null) {
zkp.close();
}
}
/**
* 休息，在此期间我们有三种选择：<br>
* <ol>
* <li>永久性断开网络连接
* <li>断开网络连接一段时间timespan后再连上，其中timespan<{@code TIMEOUT}
* <li>断开网络连接一段时间timespan后再连上，其中timespan>{@code TIMEOUT}
* </ol>
*/
private static void sleepForNetworkDisturbances() {
try {
Thread.sleep(2 * TIMEOUT);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
try {
connect();
} catch (IOException e) {
System.err
.println("Can't create zookeeper client, please check the network.");
}
System.out.println("Session build.");
try {
createNode();
} catch (Exception e) {
System.err.println("Create znode failed.");
}
System.out.println("znode created.");
sleepForNetworkDisturbances();
try {
String data = getData();
if (data != null) {
// 在“休息”期间做了第2件事情，Sesion没有过期，EPHEMERAL节点依然存在
System.out.println("data=" + data);
}
} catch (KeeperException e) {
e.printStackTrace();
// 在“休息”期间做了第1件事情
if (e instanceof ConnectionLossException) {
System.err
.println("Oops, network is disconnected. Retry getData().");
// 如果session没有失效，而仅仅是网络异常，则可以重新尝试获取数据，可能在重试时网络已经正常了
try {
Thread.sleep(1000);
String data = getData();
if (data != null) {
System.out.println("data=" + data);
} else {
System.out.println("can't get data.");
}
} catch (Exception e1) {
e1.printStackTrace();
}
}
// 在“休息”期间做了第3件事情，则session会过期
else if (e instanceof SessionExpiredException) {
System.err
.println("Session Expired, client will reconnect and create znode again.");
// 当发再Session Expired时，必须重新建立连接，即new一个ZooKeeper
try {
connect();
createNode();
String data = getData();
if (data != null) {
System.out.println("data=" + data);
} else {
System.out.println("can't get data.");
}
} catch (Exception e1) {
e1.printStackTrace();
}
}
} catch (InterruptedException e) {
e.printStackTrace();
}
try {
disconnect();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("Client disconnected.");
}
}
Watcher
▪可以注册watcher的方法：getData、exists、getChildren。
▪可以触发watcher的方法：create、delete、setData。连接断开的情况下触发的watcher会丢失。
▪一个Watcher实例是一个回调函数，被回调一次后就被移除了。如果还需要关注数据的变化，需要再次注册watcher。
▪New ZooKeeper时注册的watcher叫default watcher，它不是一次性的，只对client的连接状态变化作出反应。
什么样的操作会产生什么类型的事件：
|
|
event For “/path” |
event For “/path/child” |
|
create(“/path”) |
EventType.NodeCreated |
-- |
|
delete(“/path”) |
EventType.NodeDeleted |
-- |
|
setData(“/path”) |
EventType.NodeDataChanged |
-- |
|
create(“/path/child”) |
EventType.NodeChildrenChanged |
EventType.NodeCreated |
|
delete(“/path/child”) |
EventType.NodeChildrenChanged |
EventType.NodeDeleted |
|
setData(“/path/child”) |
-- |
EventType.NodeDataChanged |
什么操作会触发EventType.None？
事件类型与watcher的对应关系：
|
event For “/path” |
Default Watcher |
exists |
getData |
getChildren |
|
EventType.None |
√ |
√ |
√ |
√ |
|
EventType.NodeCreated |
|
√ |
√ |
|
|
EventType.NodeDeleted |
|
√ |
√ |
|
|
EventType.NodeDataChanged |
|
√ |
√ |
|
|
EventType.NodeChildrenChanged |
|
|
|
√ |
操作与watcher的对应关系：
|
"/path" |
"/path/child" |
|||||
|
|
exists |
getData |
getChildren |
exists |
getData |
getChildren |
|
create(“/path”) |
√ |
√ |
|
|
|
|
|
delete(“/path”) |
√ |
√ |
√ |
|
|
|
|
setData(“/path”) |
√ |
√ |
|
|
|
|
|
create(“/path/child”) |
|
|
√ |
√ |
√ |
|
|
delete(“/path/child”) |
|
|
√ |
√ |
√ |
√ |
|
setData(“/path/child”) |
|
|
|
√ |
√ |
|
import java.io.IOException;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.data.Stat;
/**
*
* @description Zookeeper Watcher演示类
* @author zhangchaoyang
* @date 2014-6-22
*/
public class WatcherDemo {
private static ZooKeeper zkp = null;
private static final int TIMEOUT = 6000;
private static Watcher getWatcher(final String msg) {
return new Watcher() {
@Override
public void process(WatchedEvent event) {
System.out.println(msg + "上的监听被触发\t事件类型" + event.getType()
+ "\t发生变化的节点" + event.getPath());
}
};
}
public static void main(String[] args) throws IOException, KeeperException,
InterruptedException {
System.out.println("--------------1----------------");
zkp = new ZooKeeper("192.168.119.96:2181/app/learn", TIMEOUT,
getWatcher("CONNECT"));
Thread.sleep(1000);
System.out.println("--------------2----------------");
zkp.create("/znodename", "znodedata".getBytes(), Ids.OPEN_ACL_UNSAFE,
CreateMode.PERSISTENT);
zkp.create("/znodename/childnode", new byte[0], Ids.OPEN_ACL_UNSAFE,
CreateMode.PERSISTENT);
Stat stat = zkp.exists("/znodename", getWatcher("EXISTS"));
zkp.getChildren("/", getWatcher("GETCHILDREN"));
zkp.getData("/znodename", getWatcher("GETDATA"), stat);
stat = zkp.exists("/znodename/childnode", getWatcher("EXISTS"));
zkp.getChildren("/znodename", getWatcher("GETCHILDREN"));
zkp.getData("/znodename/childnode", getWatcher("GETDATA"), stat);
// zkp.close();
zkp = new ZooKeeper("192.168.119.96:2181/app/learn", TIMEOUT,
getWatcher("CONNECT"));
Thread.sleep(1000);
System.out.println("--------------3----------------");
zkp.delete("/znodename/childnode", -1);
zkp.delete("/znodename", -1);
zkp.close();
}
}
import java.io.IOException;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.KeeperException.ConnectionLossException;
import org.apache.zookeeper.KeeperException.SessionExpiredException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.EventType;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.Stat;
/**
*
* @description 自定义持久性的zookeeper watcher
* @author zhangchaoyang
* @date 2014-6-22
*/
public class PersistWatcher {
private static final int TIMEOUT = 6000;
private static final String znode = "/globalconfnode";
private static String globalConfData = "";
private static Watcher getConnectWatcher() {
return new Watcher() {
@Override
public void process(WatchedEvent event) {
if (event.getType().equals(EventType.None)) {
System.out.println("连接状态发生变化。");
}
}
};
}
private static Watcher getExistsWatcher(final ZooKeeper zkp) {
return new Watcher() {
@Override
public void process(WatchedEvent event) {
try {
if (event.getType().equals(EventType.NodeDataChanged)
|| event.getType().equals(EventType.NodeCreated)) {
// 节点被创建或修改时更新缓存中的值
Stat stat = zkp.exists(znode, this);// 再次注册监听
String data = new String(
zkp.getData(znode, false, stat));
globalConfData = data;
} else if (event.getType().equals(EventType.NodeDeleted)) {
// 节点被删除时报警
System.out
.println("global configuration node have been deleted!");
try {
// 再次注册监听
zkp.exists(znode, this);
} catch (KeeperException e) {
if (e instanceof ConnectionLossException) {
System.out.println("连接已断开。");
}
}
}
} catch (KeeperException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
}
public static void main(String[] args) {
try {
ZooKeeper zkp = new ZooKeeper("192.168.119.96:2181/app/learn",
TIMEOUT,
getConnectWatcher());
zkp.exists(znode, getExistsWatcher(zkp));
zkp.create(znode, "config_value".getBytes(), Ids.OPEN_ACL_UNSAFE,
CreateMode.EPHEMERAL);
Thread.sleep(500);// 修改节点后必须sleep，等待watcher回调完成
System.out.println(globalConfData);
for (int i = 0; i < 4; i++) {
zkp.setData(znode, ("config_value" + i).getBytes(), -1);
Thread.sleep(500);// 修改节点后必须sleep，等待watcher回调完成
System.out.println(globalConfData);
}
zkp.close();// EPHEMERAL节点会被删除，但Session并不会马上失效(只不过ConnectionLoss了)，所以还是会触发watcher
try {
// 此时Session已失效
zkp.exists(znode, false);
} catch (KeeperException e) {
if (e instanceof SessionExpiredException)
System.out.println("Session已失效。");
}
} catch (IOException e) {
e.printStackTrace();
} catch (KeeperException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
ACL
▪每个节点有单独的ACL，子节点不能继承父节点的ACL
▪ACL有三个维度：schema,id,permision
▪Schema有7种：
▪world: 它下面只有一个id, 叫anyone
▪auth: 它不需要id
▪digest: 它对应的id为username:BASE64(SHA1(password))
▪ip: 它对应的id为客户机的IP地址，设置的时候可以设置一个ip段，比如ip:192.168.1.0/16, 表示匹配前16个bit的IP段
▪super: 在这种scheme情况下，对应的id拥有超级权限
▪sasl: sasl的对应的id，是一个通过了kerberos认证的用户id
▪Permission有5种:
▪CREATE(c),DELETE(d),READ(r),WRITE(w),ADMIN(a)
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.KeeperException.NoAuthException;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.ACL;
/**
*
* @description Zookeeper ACL演示类
* @author zhangchaoyang
* @date 2014-6-22
*/
public class AclDemo {
private static final int TIMEOUT = 6000;
public static void main(String[] args) throws IOException, KeeperException,
InterruptedException {
ZooKeeper zkp = new ZooKeeper("192.168.119.96:2181/app/learn", TIMEOUT,
null);
String schema = "digest";// schema类型有：world,auth,digest,ip,super
String auth = "username:password";
zkp.addAuthInfo(schema, auth.getBytes());
List<ACL> acls = new ArrayList<ACL>();
for (ACL id : Ids.CREATOR_ALL_ACL) {
acls.add(id);
}
zkp.create("/znodename", "znodedata".getBytes(), acls,
CreateMode.PERSISTENT);
ZooKeeper zoo = null;
try {
zoo = new ZooKeeper("192.168.119.96:2181/app/learn", TIMEOUT, null);
System.out.println("采用不合法的认证方式：");
String badAuthentication = "username:wrongpass";
zoo.addAuthInfo(schema, badAuthentication.getBytes());
zoo.getData("/znodename", null, null);
} catch (KeeperException e) {
if (e instanceof NoAuthException) {
System.out.println("认证失败：" + e.getMessage());
}
System.out.println("采用合法的认证方式：");
zoo.addAuthInfo(schema, auth.getBytes());
String data = new String(zoo.getData("/znodename", null, null));
if (data != null) {
System.out.println("认证成功：data=" + data);
}
} finally {
if (zoo != null && zoo.getState().isAlive()) {
zoo.close();
}
}
zkp.delete("/znodename", -1);
zkp.close();
}
}
开源工具menagerie
▪基于ZooKeeper实现了分布式的：
▪ReentrantZkLock
▪ReentrantZkReadWriteLock
▪Semaphore
▪CyclicBarrier
▪CountDownLatch
▪BlockingQueue
▪HashMap
▪ListSet
import java.io.IOException;
import java.util.Date;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import org.apache.log4j.Logger;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.KeeperState;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.ZooKeeper.States;
/**
*
* @description 使用ZooKeeper实现分布式锁
* @author zhangchaoyang
* @date 2014-6-22
*/
public class ZooKeeperLock {
private static Logger logger = Logger.getLogger(ZooKeeperLock.class);
private static ZooKeeper zk = null;
private static final int TIMEOUT = 1000 * 60;
private static String connStr = null;
public static void setServerPath(String path) {
connStr = path + "/app/bqas/lock";
logger.info("ZooKeeperLock zookeeper node:" + connStr);
}
public static boolean getLock(String lockname) throws KeeperException,
InterruptedException, IOException {
connect(connStr, TIMEOUT);
if (lockname.contains("-")) {
throw new RuntimeException("锁名称不能包含'-'");
}
boolean lock = false;
String path = zk.create("/" + lockname + "-", new byte[0],
Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
int selfIndex = getIndex(path);
List<String> children = zk.getChildren("/", false);
int min = getMinIndex(children);
if (min == selfIndex) {
lock = true;
}
return lock;
}
public static void releaseLock(String lockname)
throws InterruptedException, KeeperException {
disconnect();
}
private static int getIndex(String str) {
int index = -1;
int pos = str.lastIndexOf("-");
if (pos >= 0) {
try {
index = Integer.parseInt(str.substring(pos + 1));
} catch (NumberFormatException e) {
e.printStackTrace();
}
}
return index;
}
private static int getMinIndex(List<String> list) {
int min = Integer.MAX_VALUE;
for (String ele : list) {
int index = getIndex(ele);
if (index < 0) {
throw new RuntimeException("SEQUENTIAL节点名中不包含数字：" + ele);
}
if (index < min) {
min = index;
}
}
return min;
}
private static void waitUntilConnected(CountDownLatch connectedLatch) {
if (States.CONNECTING == zk.getState()) {
try {
connectedLatch.await();
} catch (InterruptedException e) {
throw new IllegalStateException(e);
}
}
}
public static boolean connect(String hostPath, int sessionTimeout) {
if (zk == null || zk.getState() == States.CLOSED) {
try {
CountDownLatch connectedLatch = new CountDownLatch(1);
Watcher watcher = new ConnectedWatcher(connectedLatch);
zk = new ZooKeeper(hostPath, sessionTimeout, watcher);
waitUntilConnected(connectedLatch);
} catch (Exception e) {
logger.error("Connect to Zookeeper failed:", e);
return false;
}
}
return true;
}
public static boolean disconnect() {
if (zk != null) {
if (States.CLOSED != zk.getState()) {
try {
zk.close();
} catch (InterruptedException e) {
logger.error("Disconnect from Zookeeper failed:", e);
return false;
}
}
}
return true;
}
static class ConnectedWatcher implements Watcher {
private CountDownLatch connectedLatch;
ConnectedWatcher(CountDownLatch connectedLatch) {
this.connectedLatch = connectedLatch;
}
@Override
public void process(WatchedEvent event) {
// 事件状态为SyncConnected时，说明与服务端的连接已建立好
if (event.getState() == KeeperState.SyncConnected) {
connectedLatch.countDown();
}
}
}
public static void main(String[] args) {
String lockname = "writeHitCount2DBlock";
System.out.println("begin to run.");
ZooKeeperLock.setServerPath("192.168.119.96:2181");
try {
boolean havelock = ZooKeeperLock.getLock(lockname);
if (havelock) {
Date date = new Date();
System.out
.println("I got the lock,and I will write DB!" + date);
Thread.sleep(1000);// 休息一段时间之后再释放锁
}
System.out.println("Job done, I will release the lock.");
ZooKeeperLock.releaseLock(lockname);
} catch (KeeperException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
本文来自博客园，作者：张朝阳，转载请注明原文链接：https://www.cnblogs.com/zhangchaoyang/articles/3813217.html
