分布式缓存技术之Redis_Redis集群连接及底层源码分析
**本次源码分析基于: jedis-3.0.1 **
1. Jedis 单点连接
当是单点服务时，Java 连接Redis的客户端:
Jedis jedis = null;
try {
jedis = new Jedis("192.168.237.130", 6379);
jedis.hset("hashzz", "k1", "v1");
} catch (Exception e) {
System.out.println(e);
e.printStackTrace();
} finally {
if (null != jedis) {
jedis.disconnect();
}
}
或者
JedisPool pool = null;
try {
pool = new JedisPool("192.168.237.130", 6379);
pool.getResource().hset("hashzz", "k2", "v2");
} catch (Exception e) {
System.out.println(e);
e.printStackTrace();
} finally {
if (null != pool) {
pool.close();
}
}
2. Jedis 基于sentinel连接
基本使用
当为了避免单点故障而使用集群环境，哨兵sentinel会对master进行监听并在master无效时进行重新选举，此种情况不能在Java中直接指定master的IP,port，Jedis提供了sentinel的方式进行连接:
// sentinel 哨兵
// sentinel.conf 中配置的master名称
String masterName = "mymaster";
// sentinel 集群环境
Set<String> sentinelIps = new HashSet<>();
sentinelIps.add("192.168.237.129:26370");
sentinelIps.add("192.168.237.130:26370");
JedisSentinelPool sentinelPool = null;
Jedis jedis = null;
try {
sentinelPool = new JedisSentinelPool(masterName, sentinelIps);
jedis = sentinelPool.getResource();
for (int i = 0; i< 10; i++) {
jedis.lpush("javaRedisClientList" + jedis.getClient().getHost(), new Integer(i).toString());
}
} catch (Exception e) {
System.out.println(e);
e.printStackTrace();
} finally {
if (jedis != null) {
jedis.disconnect();
}
if (sentinelPool != null) {
sentinelPool.close();
}
}
源码分析
- 首先查看
JedisSentinelPool的构造方法，最终都会进入如下构造方法
public JedisSentinelPool(String masterName, Set<String> sentinels,
final GenericObjectPoolConfig poolConfig, final int connectionTimeout, final int soTimeout,
final String password, final int database, final String clientName) {
this.poolConfig = poolConfig;
this.connectionTimeout = connectionTimeout;
this.soTimeout = soTimeout;
this.password = password;
this.database = database;
this.clientName = clientName;
// 初始化sentinel监听列表, 并返回当前master节点
HostAndPort master = initSentinels(sentinels, masterName);
// 初始化
initPool(master);
}
initSentinels()方法
private HostAndPort initSentinels(Set<String> sentinels, final String masterName) {
HostAndPort master = null;
boolean sentinelAvailable = false;
log.info("Trying to find master from available Sentinels...");
// 首先遍历sentinel哨兵节点
for (String sentinel : sentinels) {
final HostAndPort hap = HostAndPort.parseString(sentinel);
log.debug("Connecting to Sentinel {}", hap);
Jedis jedis = null;
try {
jedis = new Jedis(hap);
// 从当前哨兵节点获取当前master
List<String> masterAddr = jedis.sentinelGetMasterAddrByName(masterName);
// connected to sentinel...
sentinelAvailable = true;
if (masterAddr == null || masterAddr.size() != 2) {
log.warn("Can not get master addr, master name: {}. Sentinel: {}", masterName, hap);
continue;
}
master = toHostAndPort(masterAddr);
log.debug("Found Redis master at {}", master);
// 找到master,跳出循环
break;
} catch (JedisException e) {
// resolves #1036, it should handle JedisException there's another chance
// of raising JedisDataException
log.warn(
"Cannot get master address from sentinel running @ {}. Reason: {}. Trying next one.", hap,
e.toString());
} finally {
if (jedis != null) {
jedis.close();
}
}
}
if (master == null) {
// 从哨兵列表中不能获取master
if (sentinelAvailable) {
// 哨兵是可用的,则可能是master有问题
// can connect to sentinel, but master name seems to not
// monitored
throw new JedisException("Can connect to sentinel, but " + masterName
+ " seems to be not monitored...");
} else {
// 所有哨兵可能都宕机不可用
throw new JedisConnectionException("All sentinels down, cannot determine where is "
+ masterName + " master is running...");
}
}
// 进行到这里，master和sentinel都是可用的
log.info("Redis master running at " + master + ", starting Sentinel listeners...");
for (String sentinel : sentinels) {
// 为每个sentinel启动一个后台线程监听
final HostAndPort hap = HostAndPort.parseString(sentinel);
MasterListener masterListener = new MasterListener(masterName, hap.getHost(), hap.getPort());
// whether MasterListener threads are alive or not, process can be stopped
masterListener.setDaemon(true);
masterListeners.add(masterListener);
masterListener.start();
}
return master;
}
- 内部类 MasterListener
protected class MasterListener extends Thread {
protected String masterName;
protected String host;
protected int port;
protected long subscribeRetryWaitTimeMillis = 5000;
protected volatile Jedis j;
protected AtomicBoolean running = new AtomicBoolean(false);
protected MasterListener() {
}
public MasterListener(String masterName, String host, int port) {
super(String.format("MasterListener-%s-[%s:%d]", masterName, host, port));
this.masterName = masterName;
this.host = host;
this.port = port;
}
public MasterListener(String masterName, String host, int port,
long subscribeRetryWaitTimeMillis) {
this(masterName, host, port);
this.subscribeRetryWaitTimeMillis = subscribeRetryWaitTimeMillis;
}
@Override
public void run() {
running.set(true);
while (running.get()) {
j = new Jedis(host, port);
try {
// double check that it is not being shutdown
if (!running.get()) {
break;
}
/*
* Added code for active refresh
*/
// 根据哨兵sentinel连接获取当前master
List<String> masterAddr = j.sentinelGetMasterAddrByName(masterName);
if (masterAddr == null || masterAddr.size() != 2) {
log.warn("Can not get master addr, master name: {}. Sentinel: {}：{}.",masterName,host,port);
}else{
initPool(toHostAndPort(masterAddr));
}
// 基于redis 频道发布订阅(channel pub/sub)实现的java内部master选举的监听
j.subscribe(new JedisPubSub() {
@Override
public void onMessage(String channel, String message) {
log.debug("Sentinel {}:{} published: {}.", host, port, message);
// 订阅的频道发来消息
String[] switchMasterMsg = message.split(" ");
if (switchMasterMsg.length > 3) {
if (masterName.equals(switchMasterMsg[0])) {
// 收到的消息 第一节数据 是 sentinel.conf 内配置的 master名称
// 根据订阅到的新的master信息, 重新初始化 master
initPool(toHostAndPort(Arrays.asList(switchMasterMsg[3], switchMasterMsg[4])));
} else {
log.debug(
"Ignoring message on +switch-master for master name {}, our master name is {}",
switchMasterMsg[0], masterName);
}
} else {
log.error(
"Invalid message received on Sentinel {}:{} on channel +switch-master: {}", host,
port, message);
}
}
// 订阅选举频道 : +switch-master
}, "+switch-master");
} catch (JedisException e) {
if (running.get()) {
log.error("Lost connection to Sentinel at {}:{}. Sleeping 5000ms and retrying.", host,
port, e);
try {
Thread.sleep(subscribeRetryWaitTimeMillis);
} catch (InterruptedException e1) {
log.error("Sleep interrupted: ", e1);
}
} else {
log.debug("Unsubscribing from Sentinel at {}:{}", host, port);
}
} finally {
j.close();
}
}
}
public void shutdown() {
try {
log.debug("Shutting down listener on {}:{}", host, port);
running.set(false);
// This isn't good, the Jedis object is not thread safe
if (j != null) {
j.disconnect();
}
} catch (Exception e) {
log.error("Caught exception while shutting down: ", e);
}
}
}
可见Java Jedis连接Redis集群是基于哨兵集群的监听，首先传入哨兵的地址，根据哨兵信息及哨兵的内部通信得到当前的master连接redis客户端，然后后台为每个哨兵分配线程，线程内基于redis channel pub/sub来设立监听，如果有新的master选举，java内部订阅到消息之后重新对master进行初始化。
