HBase学习笔记1

转载请标注原链接：http://www.cnblogs.com/xczyd/p/5577124.html

客户在使用HBase的时候，经常会抱怨说写入太慢，并发上不去等等。从前我遇到这种情况，一般都二话不说，直接去看HBase集群的负载，看看有什么性能瓶颈等等。

某老司机说，且慢，先看看用户怎么写的客户端访问HBase集群的代码。

于是花了一些时间去看。

不看不知道，一看就吓尿。客户（也包括我们自己的实施）写出来的客户端，很多时候存在很多低级错误，比如：

（1）滥用sychronize；

（2）创建了连接不释放；

（3）明明只需要调用一次的API，却进行了多次调用，要是碰巧遇到比较花时间的API，那性能就可想而知了；

（4）其他各种幺蛾子...

为此，本篇仅从HBase的Java API入手，通过源码分析和简单的实验，找到最合适Java API调用方法（主要服务于高并发场景）。

如果对HBase的Java API不熟悉的话，可以先去官网看一下文档。

下面开始正文：

使用Java API与HBase集群交互时，需要先创建一个HTable的实例，再使用该实例提供的方法来进行插入/删除/查询等操作。

要创建HTable对象，要先创建一个包含了HBase集群信息的配置实例Configuration conf，其一般创建方法如下：

Configuration conf = HBaseConfiguration.create();
//设置HBase集群的IP和端口
conf.set("hbase.zookeeper.quorum", "XX.XXX.X.XX");
conf.set("hbase.zookeeper.property.clientPort", "2181");

在拥有了conf之后，可以通过HTable提供的如下两种构造方法来创建HTable实例：

方法一：直接利用conf来创建HTable实例

对应的构造函数如下：

public HTable(Configuration conf, final TableName tableName)
  throws IOException {
    this.tableName = tableName;
    this.cleanupPoolOnClose = this.cleanupConnectionOnClose = true;
    if (conf == null) {
      this.connection = null;
      return;
    }
    this.connection = HConnectionManager.getConnection(conf);
    this.configuration = conf;

    this.pool = getDefaultExecutor(conf);
    this.finishSetup();
 }

注意红色部分的代码。在这种构造方法中，会调用HConnectionManager的getConnection函数，这个函数以conf作为输入参数，来获取了一个HConnection的实例connection。熟悉odbc，jdbc的话，会知道使用Java API进行数据库操作的时候，都会创建一个类似的connection/connection pool来维护一些数据库与客户端之间相互的连接。对于Hbase来说，承担类似角色的就是HConnection。不过与oracle不同的一点是，HConnection实际上去连接的并不是HBase集群本身，而是维护其关键数据信息的Zookeeper（简称ZK）集群。有关ZK的内容在这里不做展开，不熟悉的话可以单纯地理解为一个独立的元信息管理角色。回过来看getConnection函数，其具体实现如下：

public static HConnection getConnection(final Configuration conf)
  throws IOException {
    HConnectionKey connectionKey = new HConnectionKey(conf);
    synchronized (CONNECTION_INSTANCES) {
      HConnectionImplementation connection = CONNECTION_INSTANCES.get(connectionKey);
      if (connection == null) {
        connection = (HConnectionImplementation)createConnection(conf, true);
        CONNECTION_INSTANCES.put(connectionKey, connection);
      } else if (connection.isClosed()) {
        HConnectionManager.deleteConnection(connectionKey, true);
        connection = (HConnectionImplementation)createConnection(conf, true);
        CONNECTION_INSTANCES.put(connectionKey, connection);
      }
      connection.incCount();
      return connection;
    }
}

其中，CONNECTION_INSTANCES的类型是LinkedHashMap<HConnectionKey，HConnectionImplementation>。所谓HConnectionImplementation其实就是HConnection的具体实现。继续注意红色部分的三行代码。第一行，通过conf创建了一个HConnectionKey的实例connectionKey；第二行，去CONNECTION_INSTANCES中查找是否存在与connectionKey对应的一个HConnection的实例；第三行，如果不存在，那么调用createConnection来创建一个HConnection的实例，否则直接返回刚才从Map中查找得到的HConnection对象

不嫌麻烦，再看一下HConnectionKey的构造函数和重写的hashCode函数，代码分别如下：

HConnectionKey(Configuration conf) {
    Map<String, String> m = new HashMap<String, String>();
    if (conf != null) {
      for (String property : CONNECTION_PROPERTIES) {
        String value = conf.get(property);
        if (value != null) {
          m.put(property, value);
        }
      }
    }
    this.properties = Collections.unmodifiableMap(m);

    try {
      UserProvider provider = UserProvider.instantiate(conf);
      User currentUser = provider.getCurrent();
      if (currentUser != null) {
        username = currentUser.getName();
      }
    } catch (IOException ioe) {
      HConnectionManager.LOG.warn("Error obtaining current user, skipping username in HConnectionKey", ioe);
    }
}

public int hashCode() {
    final int prime = 31;
    int result = 1;
    if (username != null) {
      result = username.hashCode();
    }
    for (String property : CONNECTION_PROPERTIES) {
      String value = properties.get(property);
      if (value != null) {
        result = prime * result + value.hashCode();
      }
    }

    return result;
}

可以看到，hashCode函数被重写以后，其返回值实际上是username的hashCode函数的返回值，而username来自于currentuser，currentuser又来自于provider，provider是由conf创建的。可以看出，只要有相同的conf，就能创建出相同的username，也就能保证HConnectionKey的hashCode函数被重写以后，能够在username相同时返回相同的值。而CONNECTION_INSTANCES是一个LinkedHashMap，其get函数会调用HConnectionKey的hashCode函数来判断该对象是否已经存在。因此，getConnection函数的本质就是根据conf信息返回connection对象，对每一个内容相同的conf，只会返回一个connection

方法二：调用createConnection方法来显式地创建Hconnection的实例，再将其作为输入参数来创建HTable实例

createConnection方法和Htable对应的构造函数分别如下：

public static HConnection createConnection(Configuration conf)　throws IOException {
    UserProvider provider = UserProvider.instantiate(conf);
    return createConnection(conf, false, null, provider.getCurrent());
}

static HConnection createConnection(final Configuration conf, final boolean managed,final ExecutorService pool, final User user)
throws IOException {
    String className = conf.get("hbase.client.connection.impl",HConnectionManager.HConnectionImplementation.class.getName());
    Class<?> clazz = null;
    try {
      clazz = Class.forName(className);
    } catch (ClassNotFoundException e) {
      throw new IOException(e);
    }
    try {
      // Default HCM#HCI is not accessible; make it so before invoking.
      Constructor<?> constructor =
        clazz.getDeclaredConstructor(Configuration.class,
          boolean.class, ExecutorService.class, User.class);
      constructor.setAccessible(true);
      return (HConnection) constructor.newInstance(conf, managed, pool, user);
    } catch (Exception e) {
      throw new IOException(e);
    }
}

public HTable(TableName tableName, HConnection connection) throws　IOException {
    this.tableName = tableName;
    this.cleanupPoolOnClose = true;
    this.cleanupConnectionOnClose = false;
    this.connection = connection;
    this.configuration = connection.getConfiguration();

    this.pool = getDefaultExecutor(this.configuration);
    this.finishSetup();
 }

可以看出，这种构造HTable的方法会通过反射来创建一个新的HConnection实例，而不像方法一中那样共享一个HConnection实例。

值得一提的是，通过此种方法创建出来的HConnection，是需要在不再使用的时候显式调用close方法去释放掉的，否则容易造成端口占用等问题。

那么，上述两种方法，在执行插入/删除/查找的时候，性能如何呢？不妨先从代码角度分析一下。为了简便，先分析HTable在执行put(插入)操作时具体做的事情。

HTable的put函数如下：

public void put(final Put put)　throws InterruptedIOException, RetriesExhaustedWithDetailsException {
    doPut(put);
    if (autoFlush) {
      flushCommits();
    }
}

private void doPut(Put put) throws InterruptedIOException, RetriesExhaustedWithDetailsException {
    if (ap.hasError()){
      writeAsyncBuffer.add(put);
      backgroundFlushCommits(true);
    }

    validatePut(put);

    currentWriteBufferSize += put.heapSize();
    writeAsyncBuffer.add(put);

    while (currentWriteBufferSize > writeBufferSize) {
      backgroundFlushCommits(false);
    }
}

private void backgroundFlushCommits(boolean synchronous) throws　InterruptedIOException, RetriesExhaustedWithDetailsException {
    try {
      do {
        ap.submit(writeAsyncBuffer, true);
      } while (synchronous && !writeAsyncBuffer.isEmpty());

      if (synchronous) {
        ap.waitUntilDone();
      }

      if (ap.hasError()) {
        LOG.debug(tableName + ": One or more of the operations have failed -" +
            " waiting for all operation in progress to finish (successfully or not)");
        while (!writeAsyncBuffer.isEmpty()) {
          ap.submit(writeAsyncBuffer, true);
        }
        ap.waitUntilDone();

        if (!clearBufferOnFail) {
          // if clearBufferOnFailed is not set, we're supposed to keep the failed operation in the
          //  write buffer. This is a questionable feature kept here for backward compatibility
          writeAsyncBuffer.addAll(ap.getFailedOperations());
        }
        RetriesExhaustedWithDetailsException e = ap.getErrors();
        ap.clearErrors();
        throw e;
      }
    } finally {
      currentWriteBufferSize = 0;
      for (Row mut : writeAsyncBuffer) {
        if (mut instanceof Mutation) {
          currentWriteBufferSize += ((Mutation) mut).heapSize();
        }
      }
    }
}

如红色部分所表示，调用顺序是put->doPut->backgroundFlushCommits->ap.submit，其中ap是类AsyncProcess的对象。因此追踪到AsyncProcess类，其代码如下：

public void submit(List<? extends Row> rows, boolean atLeastOne) throws InterruptedIOException {
    submitLowPriority(rows, atLeastOne, false);
}

public void submitLowPriority(List<? extends Row> rows, boolean atLeastOne, boolean isLowPripority) throws InterruptedIOException {
    if (rows.isEmpty()) {
      return;
    }

    // This looks like we are keying by region but HRegionLocation has a comparator that compares
    // on the server portion only (hostname + port) so this Map collects regions by server.
    Map<HRegionLocation, MultiAction<Row>> actionsByServer =　new HashMap<HRegionLocation, MultiAction<Row>>();
    List<Action<Row>> retainedActions = new ArrayList<Action<Row>>(rows.size());

    long currentTaskCnt = tasksDone.get();
    boolean alreadyLooped = false;

    NonceGenerator ng = this.hConnection.getNonceGenerator();
    do {
      if (alreadyLooped){
        // if, for whatever reason, we looped, we want to be sure that something has changed.
        waitForNextTaskDone(currentTaskCnt);
        currentTaskCnt = tasksDone.get();
      } else {
        alreadyLooped = true;
      }

      // Wait until there is at least one slot for a new task.
      waitForMaximumCurrentTasks(maxTotalConcurrentTasks - 1);

      // Remember the previous decisions about regions or region servers we put in the
      //  final multi.
      Map<Long, Boolean> regionIncluded = new HashMap<Long, Boolean>();
      Map<ServerName, Boolean> serverIncluded = new HashMap<ServerName, Boolean>();

      int posInList = -1;
      Iterator<? extends Row> it = rows.iterator();
      while (it.hasNext()) {
        Row r = it.next();
        HRegionLocation loc = findDestLocation(r, posInList);

        if (loc == null) { // loc is null if there is an error such as meta not available.
          it.remove();
        } else if (canTakeOperation(loc, regionIncluded, serverIncluded)) {
          Action<Row> action = new Action<Row>(r, ++posInList);
          setNonce(ng, r, action);
          retainedActions.add(action);
          addAction(loc, action, actionsByServer, ng);
          it.remove();
        }
      }
    } while (retainedActions.isEmpty() && atLeastOne && !hasError());

    HConnectionManager.ServerErrorTracker errorsByServer = createServerErrorTracker();
    sendMultiAction(retainedActions, actionsByServer, 1, errorsByServer, isLowPripority);
}

private HRegionLocation findDestLocation(Row row, int posInList) {
  if (row == null) throw new IllegalArgumentException("#" + id + ", row cannot be null");
  HRegionLocation loc = null;
  IOException locationException = null;
  try {
    loc = hConnection.locateRegion(this.tableName, row.getRow());
    if (loc == null) {
      locationException = new IOException("#" + id + ", no location found, aborting submit for" +
          " tableName=" + tableName +
          " rowkey=" + Arrays.toString(row.getRow()));
    }
  } catch (IOException e) {
    locationException = e;
  }
  if (locationException != null) {
    // There are multiple retries in locateRegion already. No need to add new.
    // We can't continue with this row, hence it's the last retry.
    manageError(posInList, row, false, locationException, null);
    return null;
  }

  return loc;
}

这里代码的主要实现机制是异步调用，也就是说，并非每一次put操作都是直接往HBase里面写数据的，而是等到缓存区域内的数据多到一定程度（默认设置是２Ｍ），再进行一次写操作。当然这次操作在Server端应当还是要排队执行的，具体执行机制这里不作展开。可以确定的是，HConnection在插入/查询/删除的Java API中，只是起到一个定位RegionServer的作用，在定位到RegionServer之后，操作都是由client端通过rpc调用完成的，与客户端创建的connection的数目无关。另外，locateRegion其实只有在没有命中缓存的时候才会进行rpc通信，其他时候都是直接从缓存中获取RegionServer信息，详情可以查看locateRegion的源码，这里也不再展开。

代码分析告一段落，通过分析可以确定，createConnection的方法创建出大量的HConnection并不会对写入性能有任何帮助。相反，由于白白浪费了资源，还会比getConnection更慢。但是慢多少，无法仅凭代码作出判断。

不妨简单做一个实验来验证上述论断：

服务器环境：四台linux服务器组成的HBase集群， 内存64G，ping一次平均约5ms（严谨一点的话应该再提供一下cpu核数、频率，以及磁盘转速等信息）

客户端环境：在Mac上装的ubuntu虚拟机，分配内存10G，CPU、网络和磁盘读写速度都要比物理机慢不少，但是不影响结论

实验代码如下：

public class HbaseConectionTest {

    public static void main(String[] args) throws Exception{

        Configuration conf = HBaseConfiguration.create();

        conf.set("hbase.zookeeper.quorum", "XX.XXX.X.XX");
        conf.set("hbase.zookeeper.property.clientPort", "2181");

        ThreadInfo info = new ThreadInfo();
        info.setTableNamePrefix("test");
        info.setColNames("col1,col2");
        info.setTableCount(1);
        info.setConnStrategy("CREATEWITHCONF");//CREATEWITHCONF,CREATEWITHCONN
        info.setWriteStrategy("SEPERATE");//OVERLAP,SEPERATE
        info.setLifeCycle(60000L);

        int threadCount = 100;

        for(int i=0;i<threadCount;i++){
            //createTable(tableNamePrefix+i,colNames,conf);
        }

        //
        for(int i=0;i<threadCount;i++){
            new Thread(new WriteThread(conf,info,i)).start();
        }

        //HBaseAdmin admin = new HBaseAdmin(conf);

        //System.out.println(admin.tableExists("test"));

    }

    public static void createTable(String tableName,String[] colNames,Configuration conf) {
        System.out.println("start create table "+tableName);
        try {

            HBaseAdmin hBaseAdmin = new HBaseAdmin(conf);
            if (hBaseAdmin.tableExists(tableName)) {
                System.out.println(tableName + " is exist");
                //hBaseAdmin.disableTable(tableName);
                //hBaseAdmin.deleteTable(tableName);
                return;
            }
            HTableDescriptor tableDescriptor = new HTableDescriptor(tableName);
            for(int i=0;i<colNames.length;i++) {
                tableDescriptor.addFamily(new HColumnDescriptor(colNames[i]));
            }
            hBaseAdmin.createTable(tableDescriptor);
        } catch (Exception ex) {
            ex.printStackTrace();
        }
        System.out.println("end create table "+tableName);
    }

}

//Thread执行操作的配置信息
class ThreadInfo {

    private int tableCount;

    String tableNamePrefix;
    String[] colNames;

    //CREATEBYCONF or CREATEBYCONN
    String connStrategy;

    //overlap or seperate
    String writeStrategy;

    long lifeCycle;

    public ThreadInfo(){

    }

    public int getTableCount() {
        return tableCount;
    }

    public void setTableCount(int tableCount) {
        this.tableCount = tableCount;
    }

    public String getTableNamePrefix() {
        return tableNamePrefix;
    }

    public void setTableNamePrefix(String tableNamePrefix) {
        this.tableNamePrefix = tableNamePrefix;
    }

    public String[] getColNames() {
        return colNames;
    }

    public void setColNames(String[] colNames) {
        this.colNames = colNames;
    }

    public void setColNames(String colNames) {
        if(colNames == null){
            this.colNames = null;
        }
        else{
            this.colNames = colNames.split(",");
        }
    }

    public String getWriteStrategy() {
        return writeStrategy;
    }

    public void setWriteStrategy(String writeStrategy) {
        this.writeStrategy = writeStrategy;
    }

    public String getConnStrategy() {
        return connStrategy;
    }

    public void setConnStrategy(String connStrategy) {
        this.connStrategy = connStrategy;
    }

    public long getLifeCycle() {
        return lifeCycle;
    }

    public void setLifeCycle(long lifeCycle) {
        this.lifeCycle = lifeCycle;
    }

}

class WriteThread implements Runnable{

    private Configuration conf;
    private ThreadInfo info;
    private int index;

    public WriteThread(Configuration conf,ThreadInfo info,int index){
        this.conf = conf;
        this.info = info;
        this.index = index;
    }

    @Override
    public void run(){

        String threadName = Thread.currentThread().getName();
        int operationCount = 0;

        HTable[] htables = null;
        HConnection conn = null;

        int tableCount = info.getTableCount();

        String tableNamePrefix = info.getTableNamePrefix();
        String[] colNames = info.getColNames();

        String connStrategy = info.getConnStrategy();
        String writeStrategy = info.getWriteStrategy();

        long lifeCycle = info.getLifeCycle();

        System.out.println(threadName+": started with index "+index);

        try{
            if (connStrategy.equals("CREATEWITHCONN")) {

                conn = HConnectionManager.createConnection(conf);

                if (writeStrategy.equals("SEPERATE")) {
                    htables = new HTable[1];
                    htables[0] = new HTable(TableName.valueOf(tableNamePrefix+(index%tableCount)), conn);
                }
                else if(writeStrategy.equals("OVERLAP")) {
                    htables = new HTable[tableCount];
                    for (int i = 0; i < tableCount; i++) {
                        htables[i] = new HTable(TableName.valueOf(tableNamePrefix+i), conn);
                    }
                }
                else{
                    return;
                }
            }
            else if (connStrategy.equals("CREATEWITHCONF")) {

                conn = null;

                if (writeStrategy.equals("SEPERATE")) {
                    htables = new HTable[1];
                    htables[0] = new HTable(conf,TableName.valueOf(tableNamePrefix+(index%tableCount)));
                }
                else if(writeStrategy.equals("OVERLAP")) {
                    htables = new HTable[tableCount];
                    for (int i = 0; i < tableCount; i++) {
                        htables[i] = new HTable(conf,TableName.valueOf(tableNamePrefix+i));
                    }
                }
                else{
                    return;
                }
            }
            else {
                return;
            }

            long start = System.currentTimeMillis();
            long end = System.currentTimeMillis();

            Map<HTable,HColumnDescriptor[]> table_columnFamilies = new HashMap<HTable,HColumnDescriptor[]>();
            for(int i=0;i<htables.length;i++){
                table_columnFamilies.put(htables[i],htables[i].getTableDescriptor().getColumnFamilies());
            }

            while(end-start<=lifeCycle){
                HTable table = htables.length==1?htables[0]:htables[(int)Math.random()*htables.length];
                long s1 = System.currentTimeMillis();
                double r = Math.random();
                HColumnDescriptor[] columnFamilies = table_columnFamilies.get(table);
                Put put = generatePut(threadName,columnFamilies,colNames,operationCount);
                table.put(put);
                if(r>0.999){
                    System.out.println(System.currentTimeMillis()-s1);
                }
                operationCount++;
                end = System.currentTimeMillis();
            }

            if(conn != null){
                conn.close();
            }

        }catch(Exception ex){
            ex.printStackTrace();
        }

        System.out.println(threadName+": ended with operation count:"+operationCount);
    }

    private Put generatePut(String threadName,HColumnDescriptor[] columnFamilies,String[] colNames,int operationCount){
        Put put = new Put(Bytes.toBytes(threadName+"_"+operationCount));
        for (int i = 0; i < columnFamilies.length; i++) {
            String familyName = columnFamilies[i].getNameAsString();
            //System.out.println("familyName:"+familyName);
            for(int j=0;j<colNames.length;j++){
                if(familyName.equals(colNames[j])) { //
                    String columnName = familyName+(int)(Math.floor(Math.random()*5+10*j));
                    String val = ""+columnName.hashCode()%100;
                    put.add(Bytes.toBytes(familyName),Bytes.toBytes(columnName),Bytes.toBytes(val));
                }
            }
        }
        //System.out.println(put.toString());
        return put;
    }
}

简单来说就是先创建一些有两列的HBase表，然后创建一些线程分别采用getConnection策略和createConnection策略来写１分钟的数据。当然写几张表，写多久，写什么，怎么写都可以调整。比如我这里就设计了固定写一张表或者随机写一张表几种逻辑。需要注意一下红色部分的代码，这里预先获得了要写的HBase表的列信息。做这个动作的原因是getTableDescriptor是会产生网络开销的，建议写代码时尽量少调用，以免增加不必要的额外开销（事实上这个额外开销是很巨大的）。

具体实验数据如下表所示，具体值因为网络波动等原因会有所差异。总的来说，在并发较高（线程数大于30）的时候，getConnection方法速度要明显快于createConnection；在并发较低的(线程数小于等于10)的时候，createConnection则稍微占优。另外，使用getConnection的时候，写一张表的速度在高并发场景下要明显快于写多张表，但是在低并发情况下此现象不明显；使用createConnection的时候，无论并发高低，写一张表的速度与写多张表大致相同，甚至还偏慢。

上述现象与代码分析的结果并不完全一致。不一致的地方主要包括如下两点：

（1）为什么线程少的时候，createConnection占优？理论上应该持平才是。这一点无法得到很合理的解释，存疑；

（2）为什么线程很多的时候，createConnection会慢这么多？这里猜测服务端的ZK要维护大量连接会负载过大，即便是多个regionServer在负责具体的写操作，也仍旧会导致性能下降。

这两个疑点还有待进一步论证。尽管如此，还是可以先建议大家在使用Java API与HBase交互时，尤其是处理高并发场景的时候，尽量使用getConnection的办法去创建HTable对象，避免维护不必要的connection导致浪费资源。

thread_count	table_count	conn_strategy	write_strategy	interval	result
1	1	CONF	OVERLAP	60s	10000*1=10000
5	1	CONF	OVERLAP	60s	11000*5=55000
10	1	CONF	OVERLAP	60s	12000*10=120000
30	1	CONF	OVERLAP	60s	8300*30=249000
60	1	CONF	OVERLAP	60s	6000*60=360000
100	1	CONF	OVERLAP	60s	4700*100=470000
1	1	CONN	OVERLAP	60s	12000*1=12000
5	1	CONN	OVERLAP	60s	16000*5=80000
10	1	CONN	OVERLAP	60s	10000*10=100000
30	1	CONN	OVERLAP	60s	2500*30=75000
60	1	CONN	OVERLAP	60s	1200*60=72000
100	1	CONN	OVERLAP	60s	1000*100=100000
5	5	CONF	SEPERATE	60s	10600*5=53000
10	10	CONF	SEPERATE	60s	11900*10=119000
30	30	CONF	SEPERATE	60s	6900*30=207000
60	60	CONF	SEPERATE	60s	3650*60=219000
100	100	CONF	SEPERATE	60s	2500*100=250000
5	5	CONN	SEPERATE	60s	14000*5=70000
10	10	CONN	SEPERATE	60s	10500*10=105000
30	30	CONN	SEPERATE	60s	3250*30=97500
60	60	CONN	SEPERATE	60s	1450*60=87000
100	100	CONN	SEPERATE	60s	930*100=93000