Question

使用mapreduce作业我试图从Hbase表中删除行。

我收到以下错误。

java.lang.ClassCastException: org.apache.hadoop.hbase.client.Delete cannot be cast to org.apache.hadoop.hbase.KeyValue
        at org.apache.hadoop.hbase.mapreduce.HFileOutputFormat$1.write(HFileOutputFormat.java:124)
        at org.apache.hadoop.mapred.ReduceTask$NewTrackingRecordWriter.write(ReduceTask.java:551)
        at org.apache.hadoop.mapreduce.task.TaskInputOutputContextImpl.write(TaskInputOutputContextImpl.java:85)
        at org.apache.hadoop.mapreduce.lib.reduce.WrappedReducer$Context.write(WrappedReducer.java:99)
        at org.apache.hadoop.mapreduce.Reducer.reduce(Reducer.java:144)
        at org.apache.hadoop.mapreduce.Reducer.run(Reducer.java:164)
        at org.apache.hadoop.mapred.ReduceTask.runNewReducer(ReduceTask.java:610)
        at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:444)
        at org.apache.hadoop.mapred.Child$4.run(Child.java:268)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.security.auth.Subject.doAs(Subject.java:396)
        at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.

看起来这是由configureIncrementalLoad设置为KeyValue的输出引起的。它只有PutSortReducer和KeyValueSortReducer，但不是DeleteSortReducer。

我的代码：

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.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.client.Delete;
import org.apache.hadoop.hbase.client.HTable;
import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
import org.apache.hadoop.hbase.mapreduce.HFileOutputFormat;
import org.apache.hadoop.io.LongWritable;
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.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;

public class DeleteRows extends Configured implements Tool {

    public static class Map extends
            Mapper<LongWritable, Text, ImmutableBytesWritable, Delete> {

        ImmutableBytesWritable hKey = new ImmutableBytesWritable();
        Delete delRow;

        @Override
        protected void map(LongWritable key, Text value, Context context)
                throws IOException, InterruptedException {
            hKey.set(value.getBytes());
            delRow = new Delete(hKey.get());
            context.write(hKey, delRow);
            // Update counters
            context.getCounter("RowsDeleted", "Success").increment(1);
        }
    }


    @SuppressWarnings("deprecation")
    public int run(String[] args) throws Exception {
        Configuration conf = new Configuration();
        args = new GenericOptionsParser(conf, args).getRemainingArgs();
        HBaseConfiguration.addHbaseResources(conf);

        Job job = new Job(conf, "Delete stuff!");
        job.setJarByClass(DeleteRows.class);

        job.setMapperClass(Map.class);
        job.setMapOutputKeyClass(ImmutableBytesWritable.class);
        job.setMapOutputValueClass(Delete.class);

        job.setInputFormatClass(TextInputFormat.class);
        FileInputFormat.addInputPath(job, new Path(args[0]));

        HTable hTable = new HTable(args[2]);
        // Auto configure partitioner and reducer
        HFileOutputFormat.configureIncrementalLoad(job, hTable);
        FileOutputFormat.setOutputPath(job, new Path(args[1]));

        job.waitForCompletion(true);
        return (0);
    }

    public static void main(String[] args) throws Exception {
        int exitCode = ToolRunner.run(new DeleteRows(), args);
        System.exit(exitCode);
    }
}

使用行键删除大量行是否有更好/更快的方法？显然删除映射器中的每一行是可能的，但我认为这比批量推送删除到正确的区域服务器要慢。

Answer 1

您的目标是使用Delete流生成HFile（实际上删除标记为KeyValue）。标准方法是使用HFileOutputFormat。实际上，您只能将KeyValue更改流添加到此格式中，并且有2个标准缩减器：PutSortReducer和KeyValueSortReducer。将reduce任务的数量设置为0，您实际上将所有Delete直接传递给输出格式，这当然不能正常工作。

您最明显的选择：

添加缩减器DeleteSortReducer。这种减速器非常简单，几乎可以复制。您只需从Delete中提取单个KeyValue流并对其进行排序。 PutSortReducer是您的好榜样。 Put更改未排序，因此这就是需要此类缩减器的原因。
只构建Delete的流，而不是包含删除标记的适当KeyValue流。这对速度来说可能是最好的。

Answer 2

使用TableMapReduceUtil.initTableReducerJob设置reducer而不是HFileOutputFormat.configureIncrementalLoad，代码工作正常。

TableMapReduceUtil.initTableReducerJob(tableName, null, job);
job.setNumReduceTasks(0);

但是，这仍然不会为completebulkload实用程序创建删除。它只是执行删除RPC。

使用MapReduce作业删除HBase批量删除

2 个答案: