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Tags : Jedis,一致性哈希发表时间: 2019-06-07 22:15:07
一致性哈希算法介绍:一致性哈希算法

导入Jedis依赖

<dependency>
    <groupId>redis.clients</groupId>
    <artifactId>jedis</artifactId>
    <version>2.9.0</version>
</dependency>
代码如下

import redis.clients.jedis.JedisPoolConfig;
import redis.clients.jedis.JedisShardInfo;
import redis.clients.jedis.ShardedJedis;
import redis.clients.jedis.ShardedJedisPool;
 
import java.util.Arrays;
import java.util.List;
 
public class Test {
    public static void main(String[] args) {
        //连接池配置
        JedisPoolConfig poolConfig = new JedisPoolConfig();
        poolConfig.setMaxTotal(10);
        poolConfig.setMaxIdle(1);
        poolConfig.setMaxWaitMillis(200);
        poolConfig.setTestOnBorrow(false);
        poolConfig.setTestOnReturn(false);
 
        //分片信息
        JedisShardInfo shardInfo1 = new JedisShardInfo("192.168.137.128", 6379, 500);
        JedisShardInfo shardInfo2 = new JedisShardInfo("192.168.137.129", 6379, 500);
 
        //根据分片信息创建连接池
        List<JedisShardInfo> infoList = Arrays.asList(shardInfo1, shardInfo2);
        ShardedJedisPool jedisPool = new ShardedJedisPool(poolConfig, infoList);
 
        ShardedJedis jedis = null;
        try {
            jedis = jedisPool.getResource();
            jedis.set("test", "this is a test");
        } finally {
            if(jedis!=null)
                jedis.close();
        }
 
        try {
            jedis = jedisPool.getResource();
            String value = jedis.get("test");
            System.out.println(value);
        } finally {
            if(jedis!=null)
                jedis.close();
        }
    }
}
实际效果如下:

D:\Redis-x64-2.8.2402>redis-cli.exe -h 192.168.137.128 -p 6379
192.168.137.128:6379> get test
(nil)
192.168.137.128:6379> exit
 
D:\Redis-x64-2.8.2402>redis-cli.exe -h 192.168.137.129 -p 6379
192.168.137.129:6379> get test
"this is a test"
192.168.137.129:6379> exit
由于是从连接池获取连接信息,先来看下连接池的实现方式

public class ShardedJedisPool extends Pool<ShardedJedis> {
    public ShardedJedisPool(final GenericObjectPoolConfig poolConfig, 
            List<JedisShardInfo> shards) {
        this(poolConfig, shards, Hashing.MURMUR_HASH);
    }
    
    public ShardedJedisPool(final GenericObjectPoolConfig poolConfig,
            List<JedisShardInfo> shards, Hashing algo) {
        this(poolConfig, shards, algo, null);
    }
 
    public ShardedJedisPool(final GenericObjectPoolConfig poolConfig, 
            List<JedisShardInfo> shards, Hashing algo, Pattern keyTagPattern) {          
        super(poolConfig, new ShardedJedisFactory(shards, algo, keyTagPattern));
    }
    ......
}
public abstract class Pool<T> implements Closeable {
    
    // 连接池底层使用apache common pool 2.0实现
    // import org.apache.commons.pool2.PooledObjectFactory;
    // import org.apache.commons.pool2.impl.GenericObjectPool;
    protected GenericObjectPool<T> internalPool;
 
    public Pool(final GenericObjectPoolConfig poolConfig, 
            PooledObjectFactory<T> factory) {
        initPool(poolConfig, factory);
    }
    
    // factory = ShardedJedisFactory
    public void initPool(final GenericObjectPoolConfig poolConfig, 
            PooledObjectFactory<T> factory) {
        if (this.internalPool != null) {
            try {
                closeInternalPool();
            } catch (Exception e) {}
        }
        this.internalPool = new GenericObjectPool<T>(factory, poolConfig);
    }
    ......
}
连接池初始化完成后,下一步是从连接池获取连接

public class ShardedJedisPool extends Pool<ShardedJedis> {
    ......
    @Override
    public ShardedJedis getResource() {
        ShardedJedis jedis = super.getResource();
        jedis.setDataSource(this);
        return jedis;
    }
    ......
}
public abstract class Pool<T> implements Closeable {
    ......
    public T getResource() {
        try {
            return internalPool.borrowObject();
        } catch (NoSuchElementException nse) {
               throw new JedisException("Could not get a resource from the pool", nse);
        } catch (Exception e) {
                throw new JedisConnectionException(
                        "Could not get a resource from the pool", e);
        }
    }
    ......
}
public class GenericObjectPool<T> extends BaseGenericObjectPool<T> 
        implements ObjectPool<T>, GenericObjectPoolMXBean, UsageTracking<T> {
    public T borrowObject() throws Exception {
        return this.borrowObject(this.getMaxWaitMillis());
    }
 
    public T borrowObject(long borrowMaxWaitMillis) throws Exception {
        ......
        p = (PooledObject)this.idleObjects.pollFirst();
        if(p == null) {
            p = this.create();
        ......
    }
 
    // ShardedJedisFactory
    private PooledObject<T> create() throws Exception {
        ......
        p = this.factory.makeObject();
        ......
    }
    ......
}
看下ShardedJedisFactory的实现

public class ShardedJedisPool extends Pool<ShardedJedis> {
    ......
    private static class ShardedJedisFactory 
            implements PooledObjectFactory<ShardedJedis> {
        
        private List<JedisShardInfo> shards;
        private Hashing algo;
        private Pattern keyTagPattern;
        
        // shards = 分片信息
        // algo = Hashing.MURMUR_HASH
        // keyTagPattern = null
        public ShardedJedisFactory(List<JedisShardInfo> shards, 
                Hashing algo, Pattern keyTagPattern) {
            this.shards = shards;
            this.algo = algo;
            this.keyTagPattern = keyTagPattern;
        }
 
        @Override
        public PooledObject<ShardedJedis> makeObject() throws Exception {
            ShardedJedis jedis = new ShardedJedis(shards, algo, keyTagPattern);
            return new DefaultPooledObject<ShardedJedis>(jedis);
        }
        ......
    }
    ......
}
每个连接都保存了所有的Redis实例信息

public class ShardedJedis extends BinaryShardedJedis 
        implements JedisCommands, Closeable {
 
    // shards = 分片信息
    // algo = Hashing.MURMUR_HASH
    // keyTagPattern = null
    public ShardedJedis(List<JedisShardInfo> shards, Hashing algo, Pattern keyTagPattern) {
        super(shards, algo, keyTagPattern);
    }
    ......
}
public class BinaryShardedJedis extends Sharded<Jedis, JedisShardInfo> 
        implements BinaryJedisCommands {
 
    // shards = 分片信息
    // algo = Hashing.MURMUR_HASH
    // keyTagPattern = null
    public BinaryShardedJedis(List<JedisShardInfo> shards, Hashing algo, 
            Pattern keyTagPattern) {
        super(shards, algo, keyTagPattern);
    }
    ......
}
使用Redis实例信息构建一致性哈希环

public class Sharded<R, S extends ShardInfo<R>> {
    // TreeMap<hashkey, "192.168.137.128:6379">
    private TreeMap<Long, S> nodes;
    // Map<"192.168.137.128:6379", Jedis>
    private final Map<ShardInfo<R>, R> resources = 
            new LinkedHashMap<ShardInfo<R>, R>();
 
    // shards = 分片信息
    // algo = Hashing.MURMUR_HASH
    // keyTagPattern = null
    public Sharded(List<S> shards, Hashing algo, Pattern tagPattern) {
        this.algo = algo;
        this.tagPattern = tagPattern;
        initialize(shards);
    }
 
    // 构建一致性哈希环
    private void initialize(List<S> shards) {
        nodes = new TreeMap<Long, S>();
        
        for (int i = 0; i != shards.size(); ++i) {
            final S shardInfo = shards.get(i);
            if (shardInfo.getName() == null) 
                // 乘160是为了构建虚拟节点
                for (int n = 0; n < 160 * shardInfo.getWeight(); n++) {
                    nodes.put(this.algo.hash("SHARD-" + i + "-NODE-" + n), shardInfo);
                }
            else 
                for (int n = 0; n < 160 * shardInfo.getWeight(); n++) {
                    nodes.put(this.algo.hash(shardInfo.getName() 
                            + "*" + shardInfo.getWeight() + n), shardInfo);
                }
            resources.put(shardInfo, shardInfo.createResource());
        }
    }
向Redis中设置缓时,根据缓存的key确定写入的Redis实例

public class ShardedJedis extends BinaryShardedJedis 
        implements JedisCommands, Closeable {
 
    // key = "test", value = "this is a test"
    public String set(String key, String value) {
        Jedis j = getShard(key);
        return j.set(key, value);
    }
    ......
}  
public class Sharded<R, S extends ShardInfo<R>> {
    // TreeMap<hashkey, "192.168.137.128:6379">
    private TreeMap<Long, S> nodes;
    // Map<"192.168.137.128:6379", Jedis>
    private final Map<ShardInfo<R>, R> resources = 
            new LinkedHashMap<ShardInfo<R>, R>();
 
    public R getShard(String key) {
        return resources.get(getShardInfo(key));
    }
 
    public S getShardInfo(String key) {
        return getShardInfo(SafeEncoder.encode(getKeyTag(key)));
    }
 
    public S getShardInfo(byte[] key) {
        SortedMap<Long, S> tail = nodes.tailMap(algo.hash(key));
        if (tail.isEmpty()) {
            return nodes.get(nodes.firstKey());
        }
        return tail.get(tail.firstKey());
    }
    ......
}
 
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