Hadoop-TsFile

TsFile的Hadoop连接器实现了对Hadoop读取外部Tsfile类型的文件格式的支持。让用户可以使用Hadoop的map、reduce等操作对Tsfile文件进行读取、写入和查询。

有了这个连接器，用户可以

  • 将单个Tsfile文件加载进Hadoop，不论文件是存储在本地文件系统或者是HDFS中
  • 将某个特定目录下的所有文件加载进Hadoop，不论文件是存储在本地文件系统或者是HDFS中
  • 将Hadoop处理完后的结果以Tsfile的格式保存

系统环境要求

Hadoop 版本Java 版本TsFile 版本
2.7.31.80.10.0+

注意：关于如何下载和使用Tsfile, 请参考以下链接: https://github.com/apache/iotdb/tree/master/tsfile.

数据类型对应关系

TsFile 数据类型Hadoop writable
BOOLEANBooleanWritable
INT32IntWritable
INT64LongWritable
FLOATFloatWritable
DOUBLEDoubleWritable
TEXTText

关于TSFInputFormat的说明

TSFInputFormat继承了Hadoop中FileInputFormat类，重写了其中切片的方法。

目前的切片方法是根据每个ChunkGroup的中点的offset是否属于Hadoop所切片的startOffset和endOffset之间，来判断是否将该ChunkGroup放入此切片。

TSFInputFormat将tsfile中的数据以多个MapWritable记录的形式返回给用户。

假设我们想要从Tsfile中获得名为d1的设备的数据，该设备有三个传感器，名称分别为s1, s2, s3。

s1的类型是BOOLEAN, s2的类型是 DOUBLE, s3的类型是TEXT.

MapWritable的结构如下所示：

{
    "time_stamp": 10000000,
    "device_id":  d1,
    "s1":         true,
    "s2":         3.14,
    "s3":         "middle"
}

在Hadoop的Map job中，你可以采用如下方法获得你想要的任何值

mapwritable.get(new Text("s1"))

注意: MapWritable中所有的键值类型都是Text。

使用示例

读示例: 求和

首先，我们需要在TSFInputFormat中配置我们需要哪些数据

// configure reading time enable
TSFInputFormat.setReadTime(job, true); 
// configure reading deviceId enable
TSFInputFormat.setReadDeviceId(job, true); 
// configure reading which deltaObjectIds
String[] deviceIds = {"device_1"};
TSFInputFormat.setReadDeviceIds(job, deltaObjectIds);
// configure reading which measurementIds
String[] measurementIds = {"sensor_1", "sensor_2", "sensor_3"};
TSFInputFormat.setReadMeasurementIds(job, measurementIds);

然后，必须指定mapper和reducer输出的键和值类型

// set inputformat and outputformat
job.setInputFormatClass(TSFInputFormat.class);
// set mapper output key and value
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(DoubleWritable.class);
// set reducer output key and value
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(DoubleWritable.class);

接着，就可以编写包含具体的处理数据逻辑的mapper和reducer类了。

public static class TSMapper extends Mapper<NullWritable, MapWritable, Text, DoubleWritable> {

	@Override
	protected void map(NullWritable key, MapWritable value,
	    Mapper<NullWritable, MapWritable, Text, DoubleWritable>.Context context)
	    throws IOException, InterruptedException {
	
	  Text deltaObjectId = (Text) value.get(new Text("device_id"));
	  context.write(deltaObjectId, (DoubleWritable) value.get(new Text("sensor_3")));
	}
}

public static class TSReducer extends Reducer<Text, DoubleWritable, Text, DoubleWritable> {

	@Override
	protected void reduce(Text key, Iterable<DoubleWritable> values,
	    Reducer<Text, DoubleWritable, Text, DoubleWritable>.Context context)
	    throws IOException, InterruptedException {
	
	  double sum = 0;
	  for (DoubleWritable value : values) {
	    sum = sum + value.get();
	  }
	  context.write(key, new DoubleWritable(sum));
	}
}

注意: 完整的代码示例可以在如下链接中找到：https://github.com/apache/iotdb/blob/master/example/hadoop/src/main/java/org/apache/iotdb/hadoop/tsfile/TSFMRReadExample.java

写示例: 计算平均数并写入Tsfile中

除了OutputFormatClass，剩下的配置代码跟上面的读示例是一样的

job.setOutputFormatClass(TSFOutputFormat.class);
// set reducer output key and value
job.setOutputKeyClass(NullWritable.class);
job.setOutputValueClass(HDFSTSRecord.class);

然后，是包含具体的处理数据逻辑的mapper和reducer类。

public static class TSMapper extends Mapper<NullWritable, MapWritable, Text, MapWritable> {

    @Override
    protected void map(NullWritable key, MapWritable value,
                       Mapper<NullWritable, MapWritable, Text, MapWritable>.Context context)
            throws IOException, InterruptedException {

        Text deltaObjectId = (Text) value.get(new Text("device_id"));
        long timestamp = ((LongWritable)value.get(new Text("timestamp"))).get();
        if (timestamp % 100000 == 0) {
            context.write(deltaObjectId, new MapWritable(value));
        }
    }
}

/**
 * This reducer calculate the average value.
 */
public static class TSReducer extends Reducer<Text, MapWritable, NullWritable, HDFSTSRecord> {

    @Override
    protected void reduce(Text key, Iterable<MapWritable> values,
                          Reducer<Text, MapWritable, NullWritable, HDFSTSRecord>.Context context) throws IOException, InterruptedException {
        long sensor1_value_sum = 0;
        long sensor2_value_sum = 0;
        double sensor3_value_sum = 0;
        long num = 0;
        for (MapWritable value : values) {
            num++;
            sensor1_value_sum += ((LongWritable)value.get(new Text("sensor_1"))).get();
            sensor2_value_sum += ((LongWritable)value.get(new Text("sensor_2"))).get();
            sensor3_value_sum += ((DoubleWritable)value.get(new Text("sensor_3"))).get();
        }
        HDFSTSRecord tsRecord = new HDFSTSRecord(1L, key.toString());
        DataPoint dPoint1 = new LongDataPoint("sensor_1", sensor1_value_sum / num);
        DataPoint dPoint2 = new LongDataPoint("sensor_2", sensor2_value_sum / num);
        DataPoint dPoint3 = new DoubleDataPoint("sensor_3", sensor3_value_sum / num);
        tsRecord.addTuple(dPoint1);
        tsRecord.addTuple(dPoint2);
        tsRecord.addTuple(dPoint3);
        context.write(NullWritable.get(), tsRecord);
    }
}

注意: 完整的代码示例可以在如下链接中找到：https://github.com/apache/iotdb/blob/master/example/hadoop/src/main/java/org/apache/iotdb/hadoop/tsfile/TSMRWriteExample.java