[源码分析] Dynomite 分布式存储引擎 之 DynoJedisClient(1)

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[源码分析] Dynomite 分布式存储引擎 之 DynoJedisClient(1)

目录

0x00 摘要

前面我们有文章介绍了Amazon Dynamo系统架构 和 NetFlix Dynomite。

我们今天来看看 NetFlix Dynomite 的 Java 客户端 DynoJedisClient 如何实现。分析客户端是因为,此客户端的作用很类似于集群master,其思路是:java驱动提供多个策略接口,可以用来驱动程序行为调优。包括负载均衡,重试请求,管理节点连接等等。

因为 Dynomite 对于本文来说,过于庞大&底层,而且 DynoJedisClient 与 Dynomite 耦合过于紧密, 所以我们从最简单的功能点出发看看 DynoJedisClient,于是我们可以想到的功能点是:

  • 如何提供基本功能,即提供数据库连接池;
  • 如何管理节点连接;
  • 如何拓扑感知;
  • 如何负载均衡;
  • 如何故障转移;
  • 故障转移;

所以我们接下来就围绕这些基本功能点进行分析。

0x01 背景概念

1.1 Amazon Dynamo

亚马逊在业务发展期间面临一些问题,主要受限于关系型数据库的可扩展性和高可用性,因此研发了一套新的、基于 KV 存储模型的数据库,将之命名为 Dynamo,其主要采取完全的分布式、去中心化的架构。

相较于传统的关系型数据库 MySQLDynamo 的功能目标与之有一些细小的差别,例如: Amazon 的业务场景多数情况并不需要支持复杂查询,却要求必要的单节点故障容错性、数据最终一致性(即牺牲数据强一致优先保障可用性)、较强的可扩展性等。

1.2 NetFlix Dynomite

Dynomite 是 NetFlix 对亚马逊分布式存储引擎 Dynamo 的一个开源通用实现,它不仅支持基于内存的 K/V 数据库,还支持持久化的 Mysql、BerkeleyDb、LevelDb 等数据库,并具有简单、高效、支持跨数据中心的数据复制等优点。

Dynomite 的最终目标是提供数据库存储引擎不能提供的简单、高效、跨数据中心的数据复制功能。目前,Dynomite 已经实现了对 Redis 和 Memcached 的支持。

0x02 Netflix选型思路

Netflix选择Dynomite,是因为:

  • 其具有性能,多数据中心复制和高可用性的特点;

  • Dynomite提供分片和可插拔的数据存储引擎,允许在数据需求增加垂直和水平扩展;

  • Dynomite在Redis之上提供了高可用性、对等复制以及一致性等特性,用于构建分布式集群队列。

  • Dyno为持久连接提供连接池;

  • Dyno可以为连接池配置为拓扑感知;

  • 故障转移:Dyno为应用程序提供特定的本地机架,us-east-1a的客户端将连接到相同区域的Dynomite/Redis节点,除非该节点不可用,在这种情况下该客户端将进行故障转移。这个属性被用于通过区域划分队列。

Dynomite对于本文来说,过于底层。

所以我们重点就看看 DynoJedisClient 如何实现后面几点,当然,这几点其实也无法脱离Dynomite,我们只是力争剥离出来

0x03 基础知识

3.1 Data Center

Data Center 是由多个Rack组成的逻辑集合。

Data Center 可以是一个机房或者一个区域的设备组合。

3.2 Rack

这是一个逻辑集合,有多个彼此临近node的组成。比如一个机架上的所有物理机器。可简单的理解为存放服务器的机柜。

数据中心与机架是什么关系呢?N:1,1:N,M:N。

  • 如果只需要几台服务器就能满足业务需求,这些服务器至少有2个数据中心,那这种情况下多个数据中心可以放在1个机架上,不过这种情况对数据灾备来说是不太保险的。
  • 第2种情况是1个数据中心相当于1个机房,那机房里会有多个机架。
  • 第3种情况M:N为多个机房的多个数据中心置于多个机架上。

3.2 Rings and Tokens

由集群管理的数据就是一个环。环中的每个节点被分配一个或多个由token描述的数据范围,确定在环中的位置。

Token是用于标识每个分区的64位整数ID,范围是-2^63 -- 2^63-1。通过hash算法计算partition key的hash值,以此确定存放在哪个节点。

Token也决定了每个节点存储的数据的分布范围,每个节点保存的数据的key在(前一个节点Token,本节点Token]的半开半闭区间内,所有的节点形成一个首尾相接的环。

0x04 需求 & 思路

因为要为上层屏蔽信息,所以 DynoJedisClient 就需要应对各种复杂信息,需要对系统有深刻的了解,比如:

  • 如何维护连接,为持久连接提供连接池;
  • 如何维护拓扑;
  • 如何负载均衡;
  • 如何故障转移;
  • 如何自动重试及发现,比如自动重试挂掉的主机。自动发现集群中的其他主机。
  • 如何监控底层机架状态;

因此,DynoJedisClient 的思路是:java驱动提供多个策略接口,可以用来驱动程序行为调优。包括负载均衡,重试请求,管理节点连接等等

0x05 使用

示例代码如下:

public static void main(String[] args) throws IOException {
    final String clusterName = args[0];
    int version = Integer.parseInt(args[1]);
    final DynoQueueDemo demo = new DynoQueueDemo(clusterName, "us-east-1e");
    Properties props = new Properties();
    props.load(DynoQueueDemo.class.getResourceAsStream("/demo.properties"));
    for (String name : props.stringPropertyNames()) {
        System.setProperty(name, props.getProperty(name));
    }
    try {
        demo.initWithRemoteClusterFromEurekaUrl(args[0], 8102, false);
        if (version == 1) {
            demo.runSimpleV1Demo(demo.client);
        } else if (version == 2) {
            demo.runSimpleV2QueueDemo(demo.client);
        }
        Thread.sleep(10000);
    } catch (Exception ex) {
        ex.printStackTrace();
    } finally {
        demo.stop();
        logger.info("Done");
    }
}

以及辅助函数:

public void initWithRemoteClusterFromEurekaUrl(final String clusterName, final int port, boolean lock) throws Exception {
        initWithRemoteCluster(clusterName, getHostsFromDiscovery(clusterName), port, lock);
}
    
private void initWithRemoteCluster(String clusterName, final List<Host> hosts, final int port, boolean lock) throws Exception {
        final HostSupplier clusterHostSupplier = () -> hosts;

        if (lock)
            initDynoLockClient(clusterHostSupplier, null, "test", clusterName);
        else
            init(clusterHostSupplier, port, null);
}
    
public void initDynoLockClient(HostSupplier hostSupplier, TokenMapSupplier tokenMapSupplier, String appName,
                                   String clusterName) {
        dynoLockClient = new DynoLockClient.Builder().withApplicationName(appName)
                .withDynomiteClusterName(clusterName)
                .withTimeoutUnit(TimeUnit.MILLISECONDS)
                .withTimeout(10000)
                .withHostSupplier(hostSupplier)
                .withTokenMapSupplier(tokenMapSupplier).build();
}

0x06 配置

在 DynoJedisClient 之中,有如下重要配置类。

6.1 缺省配置

ConnectionPoolConfigurationImpl主要是提供缺省配置。

public class ConnectionPoolConfigurationImpl implements ConnectionPoolConfiguration {
    // DEFAULTS
    private static final LoadBalancingStrategy DEFAULT_LB_STRATEGY = LoadBalancingStrategy.TokenAware;
    private static final CompressionStrategy DEFAULT_COMPRESSION_STRATEGY = CompressionStrategy.NONE;

    private HostSupplier hostSupplier;
    private TokenMapSupplier tokenSupplier;
    private HostConnectionPoolFactory hostConnectionPoolFactory;
    private HashPartitioner hashPartitioner;
    private LoadBalancingStrategy lbStrategy = DEFAULT_LB_STRATEGY;
    private CompressionStrategy compressionStrategy = DEFAULT_COMPRESSION_STRATEGY;
}

6.2 策略配置

ArchaiusConnectionPoolConfiguration最主要是提供了若干策略,包括负载,压缩,重试:

  • LoadBalancingStrategy parseLBStrategy(String propertyPrefix) 是负载策略;
  • CompressionStrategy parseCompressionStrategy(String propertyPrefix) 是压缩策略;
  • RetryPolicyFactory parseRetryPolicyFactory(String propertyPrefix) 是重试策略;

具体如下:

public class ArchaiusConnectionPoolConfiguration extends ConnectionPoolConfigurationImpl {
    ......

    private final LoadBalancingStrategy loadBalanceStrategy;
    private final CompressionStrategy compressionStrategy;
    private final ErrorRateMonitorConfig errorRateConfig;
    private final RetryPolicyFactory retryPolicyFactory;
    private final DynamicBooleanProperty failOnStartupIfNoHosts;
    private final DynamicIntProperty lockVotingSize;
    
    ......
}

0x07 定义

DynoJedisClient 定义如下,我们可以看到最重要的成员变量就是连接池ConnectionPool。

public class DynoJedisClient implements JedisCommands, BinaryJedisCommands, MultiKeyCommands,ScriptingCommands, MultiKeyBinaryCommands, DynoJedisCommands {

    private final String appName;
    private final String clusterName;
    
    private final ConnectionPool<Jedis> connPool;
    
    private final AtomicReference<DynoJedisPipelineMonitor> pipelineMonitor = new AtomicReference<DynoJedisPipelineMonitor>();

    protected final DynoOPMonitor opMonitor;
    protected final ConnectionPoolMonitor cpMonitor;
}

0x08 逻辑连接池

因为 DynoJedisClient 最主要是管理连接池,所以我们首先介绍 逻辑连接池 ConnectionPoolImpl。

连接池层为应用程序抽象所有连接管理。在这里,我们可以配置所有内容,例如指定池选项,负载平衡策略,重试策略或默认一致性级别。

ConnectionPoolImpl 是核心类,其主要功能是:

  • 对于从HostSupplier获得的各种HostConnectionPool进行维护,形成一个HostConnectionPool集合;
  • 对于HostSupplier检测到的hosts,进行添加删除;
  • 从HostConnectionPool提取Connection,进行Operation的执行;
  • 在执行Operation时,采用HostSelectionStrategy,比如:basically Round Robin 或者 TokenAware策略;
  • 使用health check monitor来进行错误率跟踪。health check monitor可以决定重用HostConnectionPool,以及fallback到remote数据中心的HostConnectionPools执行;
  • 使用RetryPolicy来执行operation;

具体定义如下:

public class ConnectionPoolImpl<CL> implements ConnectionPool<CL>, TopologyView {

    private final ConcurrentHashMap<Host, HostConnectionPool<CL>> cpMap = new ConcurrentHashMap<Host, HostConnectionPool<CL>>();
  
    private final ConnectionPoolHealthTracker<CL> cpHealthTracker;

    private final HostConnectionPoolFactory<CL> hostConnPoolFactory;
    private final ConnectionFactory<CL> connFactory;
    private final ConnectionPoolConfiguration cpConfiguration;
    private final ConnectionPoolMonitor cpMonitor;

    private final ScheduledExecutorService idleThreadPool = Executors.newSingleThreadScheduledExecutor();

    private final HostsUpdater hostsUpdater;
    private final ScheduledExecutorService connPoolThreadPool = Executors.newScheduledThreadPool(1);

    private HostSelectionWithFallback<CL> selectionStrategy;

    private Type poolType;
}

此时逻辑如下:

+------------------------+
|DynoJedisClient         |
|                        |
|                        |            +------------------------+
|                        |            |                        |
|          connPool +-------------->  |   ConnectionPoolImpl   |
|                        |            |                        |
|                        |            +------------------------+
+------------------------+

8.1 启动

连接池 启动逻辑是:

  • 利用hostsUpdater来获取到的host进行配置添加;
  • 启用health check monitor来进行错误率跟踪;

具体如下:

@Override
public Future<Boolean> start() throws DynoException {

        HostSupplier hostSupplier = cpConfiguration.getHostSupplier();
        HostStatusTracker hostStatus = hostsUpdater.refreshHosts();
        cpMonitor.setHostCount(hostStatus.getHostCount());

        Collection<Host> hostsUp = hostStatus.getActiveHosts();
        final ExecutorService threadPool = Executors.newFixedThreadPool(Math.max(10, hostsUp.size()));
        final List<Future<Void>> futures = new ArrayList<Future<Void>>();

    	// 利用hostsUpdater来获取到的host进行配置添加
        for (final Host host : hostsUp) {
            // Add host connection pool, but don't init the load balancer yet
            futures.add(threadPool.submit(new Callable<Void>() {
                @Override
                public Void call() throws Exception {
                    addHost(host, false);
                    return null;
                }
            }));
        }

    	// 启用health check monitor来进行错误率跟踪
        boolean success = started.compareAndSet(false, true);
        if (success) {
       
            selectionStrategy = initSelectionStrategy();
            cpHealthTracker.start();
            connPoolThreadPool.scheduleWithFixedDelay(new Runnable() {

                @Override
                public void run() {
                        HostStatusTracker hostStatus = hostsUpdater.refreshHosts();
                        cpMonitor.setHostCount(hostStatus.getHostCount());
                        Logger.debug(hostStatus.toString());
                        updateHosts(hostStatus.getActiveHosts(), hostStatus.getInactiveHosts());
                }

            }, 15 * 1000, 30 * 1000, TimeUnit.MILLISECONDS);

            MonitorConsole.getInstance().registerConnectionPool(this);
            registerMonitorConsoleMBean(MonitorConsole.getInstance());
        }
        return getEmptyFutureTask(true);
}

8.2 配置Host

启动过程中,添加host逻辑如下:

Linux Bash编程

  • 依据host获取HostConnectionPool;
  • 把HostConnectionPool加入到集合;
  • 把 host,HostConnectionPool加入到选择策略selectionStrategy;
  • 依据host设置health check monitor;

具体如下:

public boolean addHost(Host host, boolean refreshLoadBalancer) {

        HostConnectionPool<CL> connPool = cpMap.get(host);

        final HostConnectionPool<CL> hostPool = hostConnPoolFactory.createHostConnectionPool(host, this);

        HostConnectionPool<CL> prevPool = cpMap.putIfAbsent(host, hostPool);
        if (prevPool == null) {
            // This is the first time we are adding this pool.
            try {
                int primed = hostPool.primeConnections();
                if (hostPool.isActive()) {
                    if (refreshLoadBalancer) {
                        selectionStrategy.addHost(host, hostPool);
                    }
                    cpHealthTracker.initializePingHealthchecksForPool(hostPool);
                    cpMonitor.hostAdded(host, hostPool);
                } else {
                    cpMap.remove(host);
                }
                return primed > 0;
            } catch (DynoException e) {
                cpMap.remove(host);
                return false;
            }
        } 
}

8.3 获取HostConnectionPool

关于获取HostConnectionPool,有同步和异步 两种实现方式,具体如下。

private class SyncHostConnectionPoolFactory implements HostConnectionPoolFactory<CL> {
        @Override
        public HostConnectionPool<CL> createHostConnectionPool(Host host, ConnectionPoolImpl<CL> parentPoolImpl) {
            return new HostConnectionPoolImpl<CL>(host, connFactory, cpConfiguration, cpMonitor);
        }
}

private class AsyncHostConnectionPoolFactory implements HostConnectionPoolFactory<CL> {
        @Override
        public HostConnectionPool<CL> createHostConnectionPool(Host host, ConnectionPoolImpl<CL> parentPoolImpl) {
            return new SimpleAsyncConnectionPoolImpl<CL>(host, connFactory, cpConfiguration, cpMonitor);
        }
}

8.4 执行

逻辑连接池 有两种执行方式:executeWithRing 与 executeWithFailover。

  • executeWithRing使用较少,所以不详细介绍。

  • executeWithFailover 是 利用selectionStrategy获取Connection,在此Connection之上进行执行。如果失败就各种重试。

public <R> OperationResult<R> executeWithFailover(Operation<CL, R> op) throws DynoException {

        RetryPolicy retry = cpConfiguration.getRetryPolicyFactory().getRetryPolicy();
        retry.begin();

        do {
            Connection<CL> connection = null;

            try {
                connection = selectionStrategy.getConnectionUsingRetryPolicy(op,
                        cpConfiguration.getMaxTimeoutWhenExhausted(), TimeUnit.MILLISECONDS, retry);

                updateConnectionContext(connection.getContext(), connection.getHost());

                OperationResult<R> result = connection.execute(op);

                // Add context to the result from the successful execution
                result.setNode(connection.getHost()).addMetadata(connection.getContext().getAll());

                retry.success();
                cpMonitor.incOperationSuccess(connection.getHost(), System.currentTimeMillis() - startTime);

                return result;

            } finally {
                if (connection != null) {
                    if (connection.getLastException() != null
                            && connection.getLastException() instanceof FatalConnectionException) {
                        connection.getParentConnectionPool().recycleConnection(connection);
                        // note - don't increment connection closed metric here;
                        // it's done in closeConnection
                    } else {
                        connection.getContext().reset();
                        connection.getParentConnectionPool().returnConnection(connection);
                    }
                }
            }

        } while (retry.allowRetry());
        throw lastException;
    }

此时逻辑如下:

                           +----------------------+
+-------------------+      |ConnectionPoolImpl    |
|DynoJedisClient    |      |                      |
|                   |      |                      |         +--------------+
|                   |      |       hostsUpdater +-------->  | HostSupplier |
|                   |      |                      |         +--------------+
|     connPool +---------> |                      |
|                   |      |                      |         +--------------------------+
|                   |      |              cpMap +-------->  |[Host, HostConnectionPool]|
+-------------------+      |                      |         |               +          |
                           +----------------------+         |               |          |
                                                            +--------------------------+
                                                                            |
                                                                            |
                                                                            |
                                                                            v
                                                            +---------------+-----+
                                                            |                     |
                                                            | HostConnectionPool  |
                                                            |                     |
                                                            +---------------------+

0x09 具体连接池

HostConnectionPool 是具体连接池实现,此类为每一个Host节点维护一个有效连接池

具体是:

  • HostConnectionPool 使用 LinkedBlockingQueue availableConnections 来维护所有有效连接,当client需要一个连接,需要从queue中提取。
  • 所以,availableConnections 就是有效连接池。
  • availableConnections 之中每一个 连接就是一个 Connection;
  • 这个 Connection (JedisConnection)是通过 JedisConnectionFactory 建立的;
  • 另外,每一个 JedisConnection 里面有:
    • HostConnectionPool hostPool;
    • Jedis jedisClient;

具体如下:

public class HostConnectionPoolImpl<CL> implements HostConnectionPool<CL> {

    // The connections available for this connection pool
    private final LinkedBlockingQueue<Connection<CL>> availableConnections = new LinkedBlockingQueue<Connection<CL>>(); 

    // Private members required by this class
    private final Host host;
    private final ConnectionFactory<CL> connFactory;
    private final ConnectionPoolConfiguration cpConfig;
    private final ConnectionPoolMonitor monitor;

    // states that dictate the behavior of the pool

    // cp not inited is the starting state of the pool. The pool will not allow connections to be borrowed in this state
    private final ConnectionPoolState<CL> cpNotInited = new ConnectionPoolNotInited();
    // cp active is where connections of the pool can be borrowed and returned
    private final ConnectionPoolState<CL> cpActive = new ConnectionPoolActive(this);
    // cp reconnecting is where connections cannot be borrowed and all returning connections will be shutdown
    private final ConnectionPoolState<CL> cpReconnecting = new ConnectionPoolReconnectingOrDown();
    // similar to reconnecting
    private final ConnectionPoolState<CL> cpDown = new ConnectionPoolReconnectingOrDown();

    // The thread safe reference to the pool state
    private final AtomicReference<ConnectionPoolState<CL>> cpState = new AtomicReference<ConnectionPoolState<CL>>(cpNotInited);
}

9.1 生成Connection

首先我们要看看 如何生成 Connection,大致就是从 connFactory 中直接获取,然后执行监控等相应操作。

@Override
public Connection<CL> createConnection() {

            try {
                Connection<CL> connection;
                if (cpConfig.isConnectToDatastore()) {
                    
                    // 具体建立连接操作
                    connection = connFactory.createConnectionWithDataStore(pool);
                    
                } else if (cpConfig.isConnectionPoolConsistencyProvided()) {
                    connection = connFactory.createConnectionWithConsistencyLevel(pool, cpConfig.getConnectionPoolConsistency());
                } else {
                    connection = connFactory.createConnection(pool);
                }

                connection.open();
                availableConnections.add(connection);

                monitor.incConnectionCreated(host);
                numActiveConnections.incrementAndGet();

                return connection;
            } 
}

9.2 JedisConnectionFactory

JedisConnectionFactory 的 createConnectionWithDataStore 函数执行了具体 建立连接操作,涉及到 Jedis 很多朋友应该都很熟悉。

简略版代码如下:

public class JedisConnectionFactory implements ConnectionFactory<Jedis> {

    private final OperationMonitor opMonitor;
    private final SSLSocketFactory sslSocketFactory;

    public JedisConnectionFactory(OperationMonitor monitor, SSLSocketFactory sslSocketFactory) {
        this.opMonitor = monitor;
        this.sslSocketFactory = sslSocketFactory;
    }

    @Override
    public Connection<Jedis> createConnectionWithDataStore(HostConnectionPool<Jedis> pool) {
        return new JedisConnection(pool, true);
    }

    // TODO: raghu compose redisconnection with jedisconnection in it
    public class JedisConnection implements Connection<Jedis> {

        private final HostConnectionPool<Jedis> hostPool;
        private final Jedis jedisClient;

        public JedisConnection(HostConnectionPool<Jedis> hostPool, boolean connectDataStore) {
            this.hostPool = hostPool;
            Host host = hostPool.getHost();

            int port = connectDataStore ? host.getDatastorePort() : host.getPort();

            if (sslSocketFactory == null) {
                JedisShardInfo shardInfo = new JedisShardInfo(host.getHostAddress(), port,
                        hostPool.getConnectionTimeout(), hostPool.getSocketTimeout(), Sharded.DEFAULT_WEIGHT);

                jedisClient = new Jedis(shardInfo);
            } else {
                JedisShardInfo shardInfo = new JedisShardInfo(host.getHostAddress(), port,
                        hostPool.getConnectionTimeout(), hostPool.getSocketTimeout(), Sharded.DEFAULT_WEIGHT,
                        true, sslSocketFactory, new SSLParameters(), null);

                jedisClient = new Jedis(shardInfo);
            }
        }

        @Override
        public HostConnectionPool<Jedis> getParentConnectionPool() {
            return hostPool;
        }

        public Jedis getClient() {
            return jedisClient;
        }
    }
}

此时逻辑如下:

                                              +----------------------+
                   +-------------------+      |ConnectionPoolImpl    |
                   |DynoJedisClient    |      |                      |
                   |                   |      |                      |         +--------------+
                   |                   |      |       hostsUpdater +-------->  | HostSupplier |
                   |                   |      |                      |         +--------------+
                   |     connPool +---------> |                      |
                   |                   |      |                      |         +--------------------------+
                   |                   |      |              cpMap +-------->  |[Host, HostConnectionPool]|
                   +-------------------+      |                      |         |               +          |
                                              +----------------------+         |               |          |
                                                                               +--------------------------+
                                                                                               |
                                                                                               |
+-----------------------------+                                                                |
| JedisConnectionFactory      |                                                                v
|                             |                                                +---------------+-------------------------------------------+
|                             |          createConnectionWithDataStore         | HostConnectionPool                                        |
|                             |                                                |                                                           |
|  sslSocketFactory           |  <------------------------------------------------+ connFactory      Host                                  |
|                             |                                                |                                                           |
|                             |                                                |  LinkedBlockingQueue<Connection<CL<> availableConnections |
+-----------------------------+                                                |                                                           |
                                                                               +------------------------------+----------------------------+
               +                                                                                              ^
               |                  +----------------------------------------+                                  |
               |                  |JedisConnection                         |                                  |
               |                  |                                        |                                  |
               |   return         |                                        |   return                         |
               |                  |     HostConnectionPool<Jedis> hostPool |                                  |
               +--------------->  |                                        | +--------------------------------+
                                  |     Jedis(shardInfo) jedisClient       |
                                  |                                        |
                                  +----------------------------------------+


手机上如下:

9.3 获取Connection

用户使用 borrowConnection 来得到 连接,并且做监控。

@Override
public Connection<CL> borrowConnection(int duration, TimeUnit unit) {
            // Start recording how long it takes to get the connection - for insight/metrics
            long startTime = System.nanoTime() / 1000;
            Connection<CL> conn = null;
            // wait on the connection pool with a timeout
            conn = availableConnections.poll(duration, unit);
            long delay = System.nanoTime() / 1000 - startTime;
            monitor.incConnectionBorrowed(host, delay);
}

0x10 拓扑

这里拓扑主要指的是token环,我们再复习下概念。

在 Dynomite 之中,由集群管理的数据就是一个环。环中的每个节点被分配一个或多个由token描述的数据范围,toekn 可以确定在环中的位置。

Token是用于标识每个分区的64位整数ID,范围是-2^63 -- 2^63-1。通过hash算法计算partition key的hash值,以此确定存放在哪个节点。

Token决定了每个节点存储的数据的分布范围,每个节点保存的数据的key在(前一个节点Token,本节点Token]的半开半闭区间内,所有的节点形成一个首尾相接的环。

10.1 只读视图

TopologyView代表了服务器拓扑的只读视图。

public interface TopologyView {
    /**
     * Retrieves a read-only view of the server topology
     *
     * @return An unmodifiable map of server-id to list of token status
     */
    Map<String, List<TokenPoolTopology.TokenStatus>> getTopologySnapshot();

    /**
     * Returns the token for the given key.
     *
     * @param key The key of the record stored in dynomite
     * @return Long The token that owns the given key
     */
    Long getTokenForKey(String key);

}

ConnectionPoolImpl 实现了 TopologyView,即 implements TopologyView

所以 ConnectionPoolImpl 本身就是一个 TopologyView。

public class ConnectionPoolImpl<CL> implements ConnectionPool<CL>, TopologyView {
    public TokenPoolTopology getTopology() {
        return selectionStrategy.getTokenPoolTopology();
    }

    @Override
    public Map<String, List<TokenPoolTopology.TokenStatus>> getTopologySnapshot() {
        return Collections.unmodifiableMap(selectionStrategy.getTokenPoolTopology().getAllTokens());
    }

    @Override
    public Long getTokenForKey(String key) {
        if (cpConfiguration
                .getLoadBalancingStrategy() == ConnectionPoolConfiguration.LoadBalancingStrategy.TokenAware) {
            return selectionStrategy.getTokenForKey(key);
        }

        return null;
    }
}  

在 DynoJedisClient 中获取 TopologyView 就是直接 获取了 ConnectionPoolImpl。

public TopologyView getTopologyView() {
		return this.getConnPool();
}

所以此时逻辑图上加入了 TopologyView 。

                                              +----------------------+
                   +-------------------+      |ConnectionPoolImpl    |
                   |DynoJedisClient    |      |                      |
                   |                   |      |                      |         +--------------+
                   |                   |      |       hostsUpdater +-------->  | HostSupplier |
                   |                   |      |                      |         +--------------+
                   |     connPool +---------> |                      |
                   |                   |      |                      |         +--------------------------+
                   |    TopologyView +------> |              cpMap +-------->  |[Host, HostConnectionPool]|
                   |                   |      |                      |         |               +          |
                   +-------------------+      +----------------------+         |               |          |
                                                                               +--------------------------+
                                                                                               |
                                                                                               |
+-----------------------------+                                                                |
| JedisConnectionFactory      |                                                                v
|                             |                                                +---------------+-------------------------------------------+
|                             |          createConnectionWithDataStore         | HostConnectionPool                                        |
|                             |                                                |                                                           |
|  sslSocketFactory           |  <------------------------------------------------+ connFactory      Host                                  |
|                             |                                                |                                                           |
|                             |                                                |  LinkedBlockingQueue<Connection<CL<> availableConnections |
+-----------------------------+                                                |                                                           |
                                                                               +------------------------------+----------------------------+
               +                                                                                              ^
               |                  +----------------------------------------+                                  |
               |                  |JedisConnection                         |                                  |
               |                  |                                        |                                  |
               |   return         |                                        |   return                         |
               |                  |     HostConnectionPool<Jedis> hostPool |                                  |
               +--------------->  |                                        | +--------------------------------+
                                  |     Jedis(shardInfo) jedisClient       |
                                  |                                        |
                                  +----------------------------------------+


手机如下:

10.2 具体实现

TokenPoolTopology 属于 拓扑 的具体实现。

getTopologySnapshot就是return map。就是得到对应了所有 rack 的 TokenStatus,这就是拓扑。

其实大家仔细想想就可以理解,拓扑不就是 “当前所有机架上分别有哪些东西,这些东西是什么状态" 的一个逻辑集合嘛

具体定义如下,其核心成员是两个:

  • map 可以理解为 rack 作为key,value 是一个list,即 "该 rack 上对应的 token status 被整理成 list";
  • rackTokenHostMap 可以理解为 rack 作为 key,value 是一个map,即 "该 rack 上的 token status <---> host 之间的关系被整理成一个 map";

这样就有两个不同维度可以分别处理这些 token了。

public class TokenPoolTopology {
    
    private final ConcurrentHashMap<String, List<TokenStatus>> map = new ConcurrentHashMap<String, List<TokenStatus>>();
    
    private final ConcurrentHashMap<String, Map<Long, Host>> rackTokenHostMap = new ConcurrentHashMap<String, Map<Long, Host>>();
  
    public ConcurrentHashMap<String, List<TokenStatus>> getAllTokens() {
        return map;
    }
  
    public void addToken(String rack, Long token, HostConnectionPool<?> hostPool) {
        List<TokenStatus> list = map.get(rack);
        if (list == null) {
            list = new ArrayList<TokenStatus>();
            map.put(rack, list);
        }

        list.add(new TokenStatus(token, hostPool));
    }

    public void addHostToken(String rack, Long token, Host host) {
        Map<Long, Host> tokenHostMap = rackTokenHostMap.get(rack);
        if (tokenHostMap == null) {
            tokenHostMap = new HashMap<>();
            rackTokenHostMap.put(rack, tokenHostMap);
        }
        tokenHostMap.put(token, host);
    }
}

10.3 如何使用

TokenPoolTopology 具体在 ConnectionPoolImpl 和 HostSelectionWithFallback 都有使用

10.3.1 ConnectionPoolImpl

ConnectionPoolImpl中如下处理,或者直接返回由上层再处理,或者就是直接返回 TokenPoolTopology 之中的所有 token 给上层:

public TokenPoolTopology getTopology() {
        return selectionStrategy.getTokenPoolTopology();
}

public Map<String, List<TokenPoolTopology.TokenStatus>> getTopologySnapshot() {
        return Collections.unmodifiableMap(selectionStrategy.getTokenPoolTopology().getAllTokens());
}

10.3.2 HostSelectionWithFallback

HostSelectionWithFallback中也有TokenPoolTopology的使用,只是用来 failover/fallback使用。

public class HostSelectionWithFallback<CL> {
    // Represents the *initial* topology from the token supplier. This does not affect selection of a host connection
    // pool for traffic. It only affects metrics such as failover/fallback
    private final AtomicReference<TokenPoolTopology> topology = new AtomicReference<>(null);
}

HostSelectionWithFallback中 也利用 host tokens 来建立或者更新已有的 TokenPoolTopology。

/**
* Create token pool topology from the host tokens
*
* @param allHostTokens
* @return tokenPoolTopology with the host information
*/
public TokenPoolTopology createTokenPoolTopology(List<HostToken> allHostTokens) {
        TokenPoolTopology topology = new TokenPoolTopology(replicationFactor.get());
    
        for (HostToken hostToken : allHostTokens) {
            String rack = hostToken.getHost().getRack();
            topology.addHostToken(rack, hostToken.getToken(), hostToken.getHost());
        }
    
        updateTokenPoolTopology(topology);
        return topology;
}

至此,连接管理和拓扑感知部分已经分析完毕,下文将继续分析自动发现和故障转移。

0xFF 参考

Cassandra系列(二):系统流程

Cassandra JAVA客户端是如何做到高性能高并发的

Cassandra之Token

http://www.ningoo.net/html/2010/cassandra_token.html

cassandra权威指南读书笔记--客户端

关于cassandra集群的数据一致性问题

黑客练手入门| pwnable.kr—幼儿瓶—01:fd

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