5、如何生成 RCFile 文件
上面说了这么多，想必你已经知道 RCFile 主要用于提升 hive 的查询效率，那如何生成这种格式的文件呢？
（1）hive 中直接通过textfile表进行insert转换例如：
insert overwrite table http_RCTable partition(dt='2013-09-30') select p_id,tm,idate,phone from tmp_testp where dt='2013-09-30';
（2）通过 mapreduce 生成目前为止，mapreduce 并没有提供内置 API 对 RCFile 进行支持，倒是 pig、hive、hcatalog 等 Hadoop生态圈里的其他项目进行了支持，究其原因是因为 RCFile 相比 textfile 等其它文件格式，对于 mapreduce 的应用场景来说没有显著的优势。
为了避免重复造轮子，下面的生成 RCFile 的 mapreduce 代码调用了 hive 和 hcatalog 的相关类，注意你在测试下面的代码时，你的 hadoop、hive、hcatalog 版本要一致，否则。。。你懂的。。。
比如我用的 hive-0.10.0+198-1.cdh4.4.0，那么就应该下载对应的版本：
PS：下面的代码已经测试通过，木有问题。
import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hive.serde2.columnar.BytesRefArrayWritable;
import org.apache.hadoop.hive.serde2.columnar.BytesRefWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.util.GenericOptionsParser;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;
import org.apache.hcatalog.rcfile.RCFileMapReduceInputFormat;
import org.apache.hcatalog.rcfile.RCFileMapReduceOutputFormat;
public class TextToRCFile extends Configured implements Tool{
public static class Map
extends Mapper<Object, Text, NullWritable, BytesRefArrayWritable>{
private byte[] fieldData;
private int numCols;
private BytesRefArrayWritable bytes;
@Override
protected void setup(Context context) throws IOException, InterruptedException {
numCols = context.getConfiguration().getInt("hive.io.rcfile.column.number.conf", 0);
bytes = new BytesRefArrayWritable(numCols);
}
public void map(Object key, Text line, Context context
) throws IOException, InterruptedException {
bytes.clear();
String[] cols = line.toString().split("\\|");
System.out.println("SIZE : "+cols.length);
for (int i=0; i<numCols; i++){
fieldData = cols[i].getBytes("UTF-8");
BytesRefWritable cu = null;
cu = new BytesRefWritable(fieldData, 0, fieldData.length);
bytes.set(i, cu);
}
context.write(NullWritable.get(), bytes);
}
}
@Override
public int run(String[] args) throws Exception {
Configuration conf = new Configuration();
String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
if(otherArgs.length < 2){
System.out.println("Usage: " +
"hadoop jar RCFileLoader.jar <main class> " +
"-tableName <tableName> -numCols <numberOfColumns> -input <input path> " +
"-output <output path> -rowGroupSize <rowGroupSize> -ioBufferSize <ioBufferSize>");
System.out.println("For test");
System.out.println("$HADOOP jar RCFileLoader.jar edu.osu.cse.rsam.rcfile.mapreduce.LoadTable " +
"-tableName test1 -numCols 10 -input RCFileLoaderTest/test1 " +
"-output RCFileLoaderTest/RCFile_test1");
System.out.println("$HADOOP jar RCFileLoader.jar edu.osu.cse.rsam.rcfile.mapreduce.LoadTable " +
"-tableName test2 -numCols 5 -input RCFileLoaderTest/test2 " +
"-output RCFileLoaderTest/RCFile_test2");
return 2;
}
/* For test
*/
String tableName = "";
int numCols = 0;
String inputPath = "";
String outputPath = "";
int rowGroupSize = 16 *1024*1024;
int ioBufferSize = 128*1024;
for (int i=0; i<otherArgs.length - 1; i++){
if("-tableName".equals(otherArgs[i])){
tableName = otherArgs[i+1];
}else if ("-numCols".equals(otherArgs[i])){
numCols = Integer.parseInt(otherArgs[i+1]);
}else if ("-input".equals(otherArgs[i])){
inputPath = otherArgs[i+1];
}else if("-output".equals(otherArgs[i])){
outputPath = otherArgs[i+1];
}else if("-rowGroupSize".equals(otherArgs[i])){
rowGroupSize = Integer.parseInt(otherArgs[i+1]);
}else if("-ioBufferSize".equals(otherArgs[i])){
ioBufferSize = Integer.parseInt(otherArgs[i+1]);
}
}
conf.setInt("hive.io.rcfile.record.buffer.size", rowGroupSize);
conf.setInt("io.file.buffer.size", ioBufferSize);
Job job = new Job(conf, "RCFile loader: loading table " + tableName + " with " + numCols + " columns");
job.setJarByClass(TextToRCFile.class);
job.setMapperClass(Map.class);
job.setMapOutputKeyClass(NullWritable.class);
job.setMapOutputValueClass(BytesRefArrayWritable.class);
// job.setNumReduceTasks(0);
FileInputFormat.addInputPath(job, new Path(inputPath));
job.setOutputFormatClass(RCFileMapReduceOutputFormat.class);
RCFileMapReduceOutputFormat.setColumnNumber(job.getConfiguration(), numCols);
RCFileMapReduceOutputFormat.setOutputPath(job, new Path(outputPath));
RCFileMapReduceOutputFormat.setCompressOutput(job, false);
System.out.println("Loading table " + tableName + " from " + inputPath + " to RCFile located at " + outputPath);
System.out.println("number of columns:" + job.getConfiguration().get("hive.io.rcfile.column.number.conf"));
System.out.println("RCFile row group size:" + job.getConfiguration().get("hive.io.rcfile.record.buffer.size"));
System.out.println("io bufer size:" + job.getConfiguration().get("io.file.buffer.size"));
return (job.waitForCompletion(true) ? 0 : 1);
}
public static void main(String[] args) throws Exception {
int res = ToolRunner.run(new Configuration(), new TextToRCFile(), args);
System.exit(res);
}
}