HBase中截断表并没有释放HDFS空间

这是因为HBase是在HDFS之上运行的，当HBase截断表的时候，它只是删除了元数据和数据目录指针，但实际上并没有删除HDFS上的数据，因此不会释放HDFS空间。为了解决这个问题，需要手动清除已删除HBase表的HDFS数据。

以下是使用Java API手动清理已删除HBase表的HDFS数据的示例代码：

public class HBaseHDFSDataCleaner {

    public static void main(String[] args) throws Exception {
        Configuration conf = HBaseConfiguration.create();
        Job job = Job.getInstance(conf, "HDFSDataCleaner");
        job.setJarByClass(HBaseHDFSDataCleaner.class);
        job.setMapperClass(HBaseHDFSDataCleanerMapper.class);
        job.setOutputKeyClass(NullWritable.class);
        job.setOutputValueClass(NullWritable.class);
        FileInputFormat.setInputPaths(job, new Path(args[0]));
        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }

    public static class HBaseHDFSDataCleanerMapper extends Mapper<LongWritable, Text, NullWritable, NullWritable> {

        private Connection conn = null;

        @Override
        protected void setup(Context context) throws IOException {
            conn = ConnectionFactory.createConnection();
        }

        @Override
        protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {

            String tableName = value.toString();
            HBaseAdmin admin = (HBaseAdmin) conn.getAdmin();

            if (admin.tableExists(TableName.valueOf(tableName))) {
                context.getCounter("HBaseCleanerMapper", "Skip Table").increment(1);
                return;
            }

            context.getCounter("HBaseCleanerMapper", "Removing Data from HDFS").increment(1);

            Configuration conf = HBaseConfiguration.create();
            HdfsHelper.delete(conf, "/" + tableName);

            context.getCounter("HBaseCleanerMapper", "Table Data Removed from HDFS").increment(1);
        }

        @Override
        protected void cleanup(Context context) throws IOException {
            if (conn != null) {
                conn