Hive中可以创建Index。
索引是标准的数据库技术，hive 0.7版本之后支持索引。hive索引采用的不是'one size fites all'的索引实现方式，而是提供插入式接口，并且提供一个具体的索引实现作为参考。
hive索引具有以下特点：
1.索引key冗余存储，提供基于key的数据视图
2.存储设计以优化查询&检索性能
3.对于某些查询减少IO，从而提高性能。
hive索引创建语句：
- CREATE INDEX index_name
- ON TABLE base_table_name (col_name, ...)
- AS 'index.handler.class.name'
- [WITH DEFERRED REBUILD]
- [IDXPROPERTIES (property_name=property_value, ...)]
- [IN TABLE index_table_name]
- [PARTITIONED BY (col_name, ...)]
- [
- [ ROW FORMAT ...] STORED AS ...
- | STORED BY ...
- ]
- [LOCATION hdfs_path]
- [TBLPROPERTIES (...)]
- [COMMENT "index comment"]
注意：
1.index的partition默认和数据表一致
2.视图上不能创建index
3. index可以通过stored as配置存储格式
重建索引：
- ALTER INDEX index_name ON table_name [PARTITION (...)] REBUILD
假如在创建索引是我们使用“ WITH
DEFERRED REBUILD”语句，则索引创建是为空，可以通过“Alter
index ... REBUILD”在一个partition上或所有partition上构建索引。
注意：
1.当hive数据更新时，必须调用该语句更新索引。
2. index
rebuild操作时一个原子操作，因此，当rebuild失败时，先前构建的索引也无法使用
删除索引：
- DROP INDEX index_name ON table_name
示例：
创建表&索引
- hive> create table index_test(id INT, name STRING)
- > partitioned by (dt STRING)
- > row format delimited fields terminated by ',';
- OK
- Time taken: 32.446 seconds
- hive> create table index_tmp(id INT, name STRING, dt STRING)
- > row format delimited fields terminated by ',';
- OK
- Time taken: 0.157 seconds
- hive> load data local inpath '/home/work/data/alter_test.txt' into table index_tmp;
- Copying data from file:/home/work/data/alter_test.txt
- Copying file: file:/home/work/data/alter_test.txt
- Loading data to table default.index_tmp
- OK
- Time taken: 1.587 seconds
- hive> set hive.exec.dynamic.partition.mode=nonstrict;
- hive> set hive.exec.dynamic.partition=true;
- hive> insert overwrite table index_test partition(dt)
- > select id,name,dt
- > from index_tmp;
- Total MapReduce jobs = 2
- ......
- OK
- Time taken: 56.103 seconds
- hive> create index index1_index_test on table index_test(id) AS 'org.apache.hadoop.hive.ql.index.compact.CompactIndexHandler' WITH DEFERRED REBUILD ;
- OK
- Time taken: 0.764 seconds
- hive> alter index index1_index_test on index_test rebuild;
- Total MapReduce jobs = 3
- ......
- OK
- Time taken: 138.589 seconds
- hive> show index on index_test;
- OK
- index1_index_test index_test id default__index_test_index1_index_test__ compact
- Time taken: 0.163 seconds
- hive> show partitions index_test;
- OK
- dt=2012-08-10
- dt=2012-08-11
- dt=2012-08-12
- Time taken: 0.17 seconds
查看索引数据：
$ hadoop fs -ls
/user/hive/warehouse/default__index_test_index1_index_test__
Found 3 items
drwxr-xr-x - work supergroup
0 2012-08-16 18:27
/user/hive/warehouse/default__index_test_index1_index_test__/dt=2012-08-10
drwxr-xr-x - work supergroup
0 2012-08-16 18:27
/user/hive/warehouse/default__index_test_index1_index_test__/dt=2012-08-11
drwxr-xr-x - work supergroup
0 2012-08-16 18:28
/user/hive/warehouse/default__index_test_index1_index_test__/dt=2012-08-12
$ hadoop fs -cat
/user/hive/warehouse/default__index_test_index1_index_test__/dt=2012-08-10/000000_0
5,hdfs://localhost:9000/user/hive/warehouse/index_test/dt=2012-08-10/000000_0,0
6,hdfs://localhost:9000/user/hive/warehouse/index_test/dt=2012-08-10/000000_0,10
7,hdfs://localhost:9000/user/hive/warehouse/index_test/dt=2012-08-10/000000_0,20
删除索引：
- hive> drop index index1_index_test on index_test;
- OK
- Time taken: 0.761 seconds
- hive> show index on index_test;
- OK
- Time taken: 0.095 seconds
索引数据也被删除
$ hadoop fs -ls
/user/hive/warehouse/default__index_test_index1_index_test__
ls: Cannot access
/user/hive/warehouse/default__index_test_index1_index_test__: No
such file or directory.