Hive：有什么方法可以自定义HiveInputFormat吗？

Question

/root/20140901/part-0
/root/20140901/part-1
/root/20140901/part-2
/root/20140902/part-0
/root/20140902/part-1
/root/20140902/part-2
/root/20140903/part-0
/root/20140903/part-1
/root/20140903/part-2

在创建命令如下所示的配置单元表之后，我调用hql=[select*from hive_combine_test where rdm>50000；]，这将花费9个映射器，与HDFS中的文件数量相同。

CREATE EXTERNAL table hive_combine_test
(id string, 
rdm string)
PARTITIONED BY (dateid string)
row format delimited fields terminated by '\t'
stored as textfile;

ALTER TABLE hive_combine_test
ADD PARTITION (dateid='20140901')
location '/root/20140901';

ALTER TABLE hive_combine_test
ADD PARTITION (dateid='20140902')
location '/root/20140902';

ALTER TABLE hive_combine_test
ADD PARTITION (dateid='20140903')
location '/root/20140903';

但我想要的是把所有的部分-I在一个分裂中，这样，应该只有三个映射器。

我尝试从org.apache.hadoop.hive.ql.io.hiveInputFormat继承，以测试自定义的JudhiveInputFormat是否可以工作。

public class JudHiveInputFormat<K extends WritableComparable, V extends Writable>
                    extends HiveInputFormat<WritableComparable, Writable> {

}

但是当我将它挂载到配置单元中时，它返回异常：

hive> add jar /my_path/jud_udf.jar;
hive> set hive.input.format=com.judking.hive.inputformat.JudHiveInputFormat;
hive> select * from hive_combine_test where rdm > 50000;

java.lang.RuntimeException: com.judking.hive.inputformat.JudCombineHiveInputFormat
    at org.apache.hadoop.hive.ql.exec.mr.ExecDriver.execute(ExecDriver.java:290)
    at org.apache.hadoop.hive.ql.exec.mr.MapRedTask.execute(MapRedTask.java:136)
    at org.apache.hadoop.hive.ql.exec.Task.executeTask(Task.java:153)
    at org.apache.hadoop.hive.ql.exec.TaskRunner.runSequential(TaskRunner.java:85)
    at org.apache.hadoop.hive.ql.Driver.launchTask(Driver.java:1472)
    at org.apache.hadoop.hive.ql.Driver.execute(Driver.java:1239)
    at org.apache.hadoop.hive.ql.Driver.runInternal(Driver.java:1057)
    at org.apache.hadoop.hive.ql.Driver.run(Driver.java:880)
    at org.apache.hadoop.hive.ql.Driver.run(Driver.java:870)
    at org.apache.hadoop.hive.cli.CliDriver.processLocalCmd(CliDriver.java:268)
    at org.apache.hadoop.hive.cli.CliDriver.processCmd(CliDriver.java:220)
    at org.apache.hadoop.hive.cli.CliDriver.processLine(CliDriver.java:423)
    at org.apache.hadoop.hive.cli.CliDriver.executeDriver(CliDriver.java:792)
    at org.apache.hadoop.hive.cli.CliDriver.run(CliDriver.java:686)
    at org.apache.hadoop.hive.cli.CliDriver.main(CliDriver.java:625)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at org.apache.hadoop.util.RunJar.main(RunJar.java:212)

有人能给我点线索吗？多谢！

Answer 1

据我所知，要在Hive中添加自定义输入/输出格式，需要在create table语句中提到该格式。像这样的事情：

CREATE TABLE (...)
ROW FORMAT DELIMITED FIELDS TERMINATED BY '\t' 
STORED AS INPUTFORMAT '<your input format class name >' OUTPUTFORMAT '<your output format class name>';

因为您只需要InputFormat,所以您的create table语句如下所示：

CREATE TABLE (...)
ROW FORMAT DELIMITED FIELDS TERMINATED BY '\t' 
STORED AS INPUTFORMAT 'JudHiveInputFormat' OUTPUTFORMAT 'org.apache.hadoop.hive.ql.io.IgnoreKeyTextOutputFormat';

为什么需要提到这个输出格式类，因为您已经覆盖了输入格式Hive也需要输出类，所以这里我们需要说Hive使用它的默认输出格式类。