Hbase源码研究（二）-------get最终转化为scan来处理（1）

    昨天和一个互联网公司的leader争执关于get和scan的问题......记得以前粗略看过一次代码，清楚的记得在0.92.1版本里get最终是转化成scan来处理的......就怪自己当时手贱，脑子笨。没记清楚具体转化步骤......今天写个博客再来分析一下。有代码有真相！！！！！！

   首先看下HTable 这个类里get方法

@Override
  public Result get(final Get get) throws IOException {
    return connection.getRegionServerWithRetries(
        new ServerCallable<Result>(connection, tableName, get.getRow(), operationTimeout) {
          public Result call() throws IOException {
            return server.get(location.getRegionInfo().getRegionName(), get);
          }
        }
    );
  }

   可以发现是调用HRegionServer里的get方法来运行的，再看HRegionServer里的get方法

  public Result get(byte[] regionName, Get get) throws IOException {
    checkOpen();
    requestCount.incrementAndGet();
    try {
      HRegion region = getRegion(regionName);
      return region.get(get, getLockFromId(get.getLockId()));
    } catch (Throwable t) {
      throw convertThrowableToIOE(cleanup(t));
    }
  }

   

   这个方法很简单，首先根据regionName得到Region，然后调用region的get方法

public Result get(final Get get, final Integer lockid) throws IOException {
    checkRow(get.getRow(), "Get");
    // Verify families are all valid
    if (get.hasFamilies()) {
      for (byte [] family: get.familySet()) {
        checkFamily(family);
      }
    } else { // Adding all families to scanner
      for (byte[] family: this.htableDescriptor.getFamiliesKeys()) {
        get.addFamily(family);
      }
    }
    List<KeyValue> results = get(get, true);
    return new Result(results);
  }

  这里面调用了另一个私有方法的get

  

private List<KeyValue> get(Get get, boolean withCoprocessor)
  throws IOException {
    List<KeyValue> results = new ArrayList<KeyValue>();

    // pre-get CP hook
    if (withCoprocessor && (coprocessorHost != null)) {
       if (coprocessorHost.preGet(get, results)) {
         return results;
       }
    }

    Scan scan = new Scan(get);

    RegionScanner scanner = null;
    try {
      scanner = getScanner(scan);
      scanner.next(results);
    } finally {
      if (scanner != null)
        scanner.close();
    }

    // post-get CP hook
    if (withCoprocessor && (coprocessorHost != null)) {
      coprocessorHost.postGet(get, results);
    }

    return results;
  }

    亮点出来了......get方法最终是转化成scan来处理的...... 后面的博客会继续分析scan ........