文章目录

• Pre
• Code
• 初始化
• 槽计算
• 无需手工调用close方法

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Pre

Redis进阶-Redis集群原理剖析及gossip协议初探 集群原理部分 简单的提了下Jest是如何实现Redis Cluster 的 ，这里我们再来梳理一下

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Code

import redis.clients.jedis.HostAndPort; import redis.clients.jedis.JedisCluster; import redis.clients.jedis.JedisPoolConfig;import java.io.IOException; import java.util.HashSet; import java.util.Set;public class JedisClusterDemo {public static void main(String[] args) throws IOException {JedisPoolConfig config = new JedisPoolConfig();config.setMaxTotal(20);config.setMaxIdle(10);config.setMinIdle(5);Set<HostAndPort> jedisClusterNode = new HashSet<HostAndPort>();jedisClusterNode.add(new HostAndPort("192.168.18.131", 8001));jedisClusterNode.add(new HostAndPort("192.168.18.131", 8004));jedisClusterNode.add(new HostAndPort("192.168.18.132", 8002));jedisClusterNode.add(new HostAndPort("192.168.18.132", 8005));jedisClusterNode.add(new HostAndPort("192.168.18.133", 8003));jedisClusterNode.add(new HostAndPort("192.168.18.133", 8006));JedisCluster jedisCluster = null;try {//connectionTimeout：指的是连接一个url的连接等待时间//soTimeout：指的是连接上一个url，获取response的返回等待时间jedisCluster = new JedisCluster(jedisClusterNode, 6000, 5000, 10, "artisan", config);System.out.println(jedisCluster.set("clusterArtisan", "artisanValue"));System.out.println(jedisCluster.get("clusterArtisan"));} catch (Exception e) {e.printStackTrace();} finally {if (jedisCluster != null)jedisCluster.close();}} }

这里是个简单的demo， 生产中用的话，需要确保jedisCluster是单例的，并且无需手工调用close，不然的话 这个连接池就关闭了，你就无法获取到连接了。

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初始化

当 Redis Cluster 的客户端来连接集群时，它也会得到一份集群的槽位配置信息并将其缓存在客户端本地。这样当客户端要查找某个 key 时，可以直接定位到目标节点。

我们来看下jedis的实现

jedisCluster = new JedisCluster(jedisClusterNode, 6000, 5000, 10, "artisan", config);

跟下源码

public JedisClusterConnectionHandler(Set<HostAndPort> nodes,final GenericObjectPoolConfig poolConfig, int connectionTimeout, int soTimeout, String password) {this.cache = new JedisClusterInfoCache(poolConfig, connectionTimeout, soTimeout, password);initializeSlotsCache(nodes, poolConfig, password);}

重点看下 initializeSlotsCache

private void initializeSlotsCache(Set<HostAndPort> startNodes, GenericObjectPoolConfig poolConfig, String password) {for (HostAndPort hostAndPort : startNodes) {Jedis jedis = new Jedis(hostAndPort.getHost(), hostAndPort.getPort());if (password != null) {jedis.auth(password);}try {cache.discoverClusterNodesAndSlots(jedis);break;} catch (JedisConnectionException e) {// try next nodes} finally {if (jedis != null) {jedis.close();}}}}

继续 cache.discoverClusterNodesAndSlots(jedis); cache为 JedisClusterInfoCache 对象。

public void discoverClusterNodesAndSlots(Jedis jedis) {w.lock();try {reset();List<Object> slots = jedis.clusterSlots();for (Object slotInfoObj : slots) {List<Object> slotInfo = (List<Object>) slotInfoObj;if (slotInfo.size() <= MASTER_NODE_INDEX) {continue;}List<Integer> slotNums = getAssignedSlotArray(slotInfo);// hostInfosint size = slotInfo.size();for (int i = MASTER_NODE_INDEX; i < size; i++) {List<Object> hostInfos = (List<Object>) slotInfo.get(i);if (hostInfos.size() <= 0) {continue;}HostAndPort targetNode = generateHostAndPort(hostInfos);setupNodeIfNotExist(targetNode);if (i == MASTER_NODE_INDEX) {assignSlotsToNode(slotNums, targetNode);}}}} finally {w.unlock();}}

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槽计算

set --------> run ----> runWithRetries ----> connectionHandler.getConnectionFromSlot(JedisClusterCRC16.getSlot(key))

CRC16算法，计算key对应的slot connectionHandler.getConnectionFromSlot(JedisClusterCRC16.getSlot(key))

public static int getSlot(byte[] key) {int s = -1;int e = -1;boolean sFound = false;for (int i = 0; i < key.length; i++) {if (key[i] == '{' && !sFound) {s = i;sFound = true;}if (key[i] == '}' && sFound) {e = i;break;}}if (s > -1 && e > -1 && e != s + 1) {return getCRC16(key, s + 1, e) & (16384 - 1);}return getCRC16(key) & (16384 - 1);}

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无需手工调用close方法

进入到set方法中看下源码

jedisCluster.set("clusterArtisan", "artisanValue")

如下：

@Overridepublic String set(final String key, final String value) {return new JedisClusterCommand<String>(connectionHandler, maxAttempts) {@Overridepublic String execute(Jedis connection) {return connection.set(key, value);}}.run(key);}

命令模式， 关注 run方法

public T run(String key) {if (key == null) {throw new JedisClusterException("No way to dispatch this command to Redis Cluster.");}return runWithRetries(SafeEncoder.encode(key), this.maxAttempts, false, false);}

继续 runWithRetries ， 截取核心逻辑

private T runWithRetries(byte[] key, int attempts, boolean tryRandomNode, boolean asking) {Jedis connection = null;try {if (asking) {......} else {if (tryRandomNode) {connection = connectionHandler.getConnection();} else {connection = connectionHandler.getConnectionFromSlot(JedisClusterCRC16.getSlot(key));}}return execute(connection);} finally {releaseConnection(connection);}}

关注点

• CRC16算法，计算key对应的slot connectionHandler.getConnectionFromSlot(JedisClusterCRC16.getSlot(key))

public static int getSlot(byte[] key) {int s = -1;int e = -1;boolean sFound = false;for (int i = 0; i < key.length; i++) {if (key[i] == '{' && !sFound) {s = i;sFound = true;}if (key[i] == '}' && sFound) {e = i;break;}}if (s > -1 && e > -1 && e != s + 1) {return getCRC16(key, s + 1, e) & (16384 - 1);}return getCRC16(key) & (16384 - 1);}

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• getConnectionFromSlot 通过 JedisPool 获取连接

关注下 JedisCluster是如何获取连接的 getConnectionFromSlot 方法

@Overridepublic Jedis getConnectionFromSlot(int slot) {JedisPool connectionPool = cache.getSlotPool(slot);if (connectionPool != null) {// It can't guaranteed to get valid connection because of node// assignmentreturn connectionPool.getResource();} else {renewSlotCache(); //It's abnormal situation for cluster mode, that we have just nothing for slot, try to rediscover stateconnectionPool = cache.getSlotPool(slot);if (connectionPool != null) {return connectionPool.getResource();} else {//no choice, fallback to new connection to random nodereturn getConnection();}}}

本质上还是通过 JedisPool 来获取一个getResource ，跟我们使用Sentinel 啊 单节点获取方法是一样的

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• finally 语句中的 releaseConnection(connection); ,自动释放连接

看下该方法

private void releaseConnection(Jedis connection) {if (connection != null) {connection.close();}}

说白了，JedisCluster set后会自动释放连接，调用的是jedis 的close方法，所以我们无需手工关闭，否则你这个jedis的连接池就挂逼了…

总结

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