生产环境应用场景描述
每天有很多事实表需要增量同步，在HIVE没有开启事务模式的条件下，需要全表重新写入HDFS中，这在需要巨大的IO时间开销，每天的增量数据占总数据的比列很小，这种方式显得非常低效。
现在的想法是，考虑利用 INSERT OVER TABLE 语句对分区表进行指定分区覆盖插入，来实现增量更新的效果。
1，首先创建测试数据集
- a、全量数据集
CREATE TABLE `ods.employees_all`( `employee_id` double,
`first_name` string,
`last_name` string,
`email` string,
`phone_number` string,
`hire_date` timestamp,
`job_id` string,
`salary` double,
`commission_pct` double,
`manager_id` double,
`department_id` int)
partitioned by (ds string)
stored as orcfile;
INSERT INTO ods.employees_all (employee_id, first_name, last_name, email, phone_number, hire_date, job_id, salary, commission_pct, manager_id, department_id, ds) VALUES(1, 'Eleni', 'Zlotkey', 'EZLOTKEY', '011.44.1344.429018', '2001-01-29 00:00:00', 'SA_MAN', 10500.0, 0.2, 100.0, 80.0, '2001');
INSERT INTO ods.employees_all (employee_id, first_name, last_name, email, phone_number, hire_date, job_id, salary, commission_pct, manager_id, department_id, ds) VALUES(2, 'Mattea', 'Marvins', 'MMARVINS', '011.44.1346.329268', '2001-01-24 00:00:00', 'SA_REP', 7200.0, 0.1, 147.0, 80.0, '2001');
INSERT INTO ods.employees_all (employee_id, first_name, last_name, email, phone_number, hire_date, job_id, salary, commission_pct, manager_id, department_id, ds) VALUES(3, 'David', 'Lee', 'DLEE', '011.44.1346.529268', '2002-02-23 00:00:00', 'SA_REP', 6800.0, 0.1, 147.0, 80.0, '2002');
INSERT INTO ods.employees_all (employee_id, first_name, last_name, email, phone_number, hire_date, job_id, salary, commission_pct, manager_id, department_id, ds) VALUES(4, 'Sundar', 'Ande', 'SANDE', '011.44.1346.629268', '2002-03-24 00:00:00', 'SA_REP', 6400.0, 0.1, 147.0, 80.0, '2002');
INSERT INTO ods.employees_all (employee_id, first_name, last_name, email, phone_number, hire_date, job_id, salary, commission_pct, manager_id, department_id, ds) VALUES(5, 'Amit', 'Banda', 'ABANDA', '011.44.1346.729268', '2003-04-21 00:00:00', 'SA_REP', 6200.0, 0.1, 147.0, 80.0, '2003');
INSERT INTO ods.employees_all (employee_id, first_name, last_name, email, phone_number, hire_date, job_id, salary, commission_pct, manager_id, department_id, ds) VALUES(6, 'shabi', 'shabi', 'shabi', '590.423.4569', '2003-06-25 00:00:00.0', 'IT_PROG', 4800.0, 0.0, 103.0, 60.0, '2003');
INSERT INTO ods.employees_all (employee_id, first_name, last_name, email, phone_number, hire_date, job_id, salary, commission_pct, manager_id, department_id, ds) VALUES(7, 'chunhuo', 'chunhuo', 'chunhuo', '590.423.4560', '2004-02-05 00:00:00.0', 'IT_PROG', 4800.0, 0.0, 103.0, 60.0, '2004');
INSERT INTO ods.employees_all (employee_id, first_name, last_name, email, phone_number, hire_date, job_id, salary, commission_pct, manager_id, department_id, ds) VALUES(8, 'Payam', 'Kaufling', 'PKAUFLIN', '650.123.3234', '2004-05-01 00:00:00.0', 'ST_MAN', 7900.0, 0.0, 100.0, 50.0, '2004');
INSERT INTO ods.employees_all (employee_id, first_name, last_name, email, phone_number, hire_date, job_id, salary, commission_pct, manager_id, department_id, ds) VALUES(9, 'David', 'Bernstein', 'DBERNSTE', '011.44.1344.345268', '2005-03-24 00:00:00.0', 'SA_REP', 9500.0, 0.25, 145.0, 80.0, '2005');
INSERT INTO ods.employees_all (employee_id, first_name, last_name, email, phone_number, hire_date, job_id, salary, commission_pct, manager_id, department_id, ds) VALUES(10, 'Ellen', 'Abel', 'EABEL', '011.44.1644.429267', '2005-05-11 00:00:00.0', 'SA_REP', 11000.0, 0.3, 149.0, 80.0, '2005');
INSERT INTO ods.employees_all (employee_id, first_name, last_name, email, phone_number, hire_date, job_id, salary, commission_pct, manager_id, department_id, ds) VALUES(11, 'Britney', 'Everett', 'BEVERETT', '650.501.2876', '2006-03-03 00:00:00.0', 'SH_CLERK', 3900.0, 0.0, 123.0, 50.0, '2006');
INSERT INTO ods.employees_all (employee_id, first_name, last_name, email, phone_number, hire_date, job_id, salary, commission_pct, manager_id, department_id, ds) VALUES(12, 'Samuel', 'McCain', 'SMCCAIN', '650.501.3876', '2006-07-01 00:00:00.0', 'SH_CLERK', 3200.0, 0.0, 123.0, 50.0, '2006');
- b、增量数据集
CREATE TABLE `ods.employees_all`( `employee_id` double,
`first_name` string,
`last_name` string,
`email` string,
`phone_number` string,
`hire_date` timestamp,
`job_id` string,
`salary` double,
`commission_pct` double,
`manager_id` double,
`department_id` int)
partitioned by (ds string)
stored as orcfile;
INSERT INTO ods.employees_tmp (employee_id, first_name, last_name, email, phone_number, hire_date, job_id, salary, commission_pct, manager_id, department_id, ds) VALUES(4, 'Sundar_update', 'Sundar_update', 'Sundar_update', '011.44.1346.629268', '2002-03-24 00:00:00', 'SA_REP', 6400.0, 0.1, 147.0, 80.0, '2002');
INSERT INTO ods.employees_tmp (employee_id, first_name, last_name, email, phone_number, hire_date, job_id, salary, commission_pct, manager_id, department_id, ds) VALUES(6, 'shabi_update', 'shabi_update', 'shabi_update', '590.423.4569', '2003-06-25 00:00:00.0', 'IT_PROG', 4800.0, 0.0, 103.0, 60.0, '2003');
INSERT INTO ods.employees_tmp (employee_id, first_name, last_name, email, phone_number, hire_date, job_id, salary, commission_pct, manager_id, department_id, ds) VALUES(8, 'Payam_update', 'Payam_update', 'Payam_update', '650.123.3234', '2004-05-01 00:00:00.0', 'ST_MAN', 7900.0, 0.0, 100.0, 50.0, '2004');
INSERT INTO ods.employees_tmp (employee_id, first_name, last_name, email, phone_number, hire_date, job_id, salary, commission_pct, manager_id, department_id, ds) VALUES(13, 'David_incremental', 'David_incremental', 'David_incremental', '011.44.1344.345268', '2007-03-24 00:00:00.0', 'SA_REP', 9500.0, 0.25, 145.0, 80.0, '2007');
INSERT INTO ods.employees_tmp (employee_id, first_name, last_name, email, phone_number, hire_date, job_id, salary, commission_pct, manager_id, department_id, ds) VALUES(14, 'Ellen_incremental', 'Ellen_incremental', 'Ellen_incremental', '011.44.1644.429267', '2007-05-11 00:00:00.0', 'SA_REP', 11000.0, 0.3, 149.0, 80.0, '2007');
INSERT INTO ods.employees_tmp (employee_id, first_name, last_name, email, phone_number, hire_date, job_id, salary, commission_pct, manager_id, department_id, ds) VALUES(15, 'Britney_incremental', 'Britney_incremental', 'Britney_incremental', '650.501.2876', '2008-03-03 00:00:00.0', 'SH_CLERK', 3900.0, 0.0, 123.0, 50.0, '2008');
INSERT INTO ods.employees_tmp (employee_id, first_name, last_name, email, phone_number, hire_date, job_id, salary, commission_pct, manager_id, department_id, ds) VALUES(16, 'Samuel_incremental', 'Samuel_incremental', 'Samuel_incremental', '650.501.3876', '2008-07-01 00:00:00.0', 'SH_CLERK', 3200.0, 0.0, 123.0, 50.0, '2008');
2，预览测试数据
-
全量
全量数据 -
增量
增量数据
3，查看全量表HDFS分区的目录情况
全量表HDFS分区目录
4，用INSER OVERWRITE TABLE语句定向更新目标分区
通过预览表数据，我知道全量表当前有12条数据，6个分区；增量表有7条数据，5个分区，其中2007和2008是新增分区，2002,2003,2004是更新分区。更新语句如下：
INSERT OVERWRITE TABLE ods.employees_all PARTITION(ds)
SELECT t1.* FROM (
SELECT a.*
FROM ods.employees_all a
LEFT join ods.employees_tmp b ON a.employee_id = b.employee_id
WHERE b.employee_id IS NULL
AND EXISTS (SELECT 1 FROM ods.employees_tmp c WHERE a.ds=c.ds )
UNION ALL
SELECT * FROM ods.employees_tmp
) t1
其中表t1的结果集为：
t1表数据集，各数据行变化或来源图中已做详细标注
这里需要解释一下的被动更新行，他的意思是这些行本身并不在新增数据集中，但因为其分区与新增数据集中的某些行的分区相同，因此也被命中以便覆盖全量数据集中的目标分区。
由t1数据集中有共有10条数据，其中新增4条，更新3条，被动更新3条，因此如果INSERT OVERWRITE TABLE语句执行成功后，ods.employees_all中应该有16条数据。
以下是更新后的全量数据集：
更新后的全量数据集
数据如预期的完全一致，说明INSERT OVERWRITE TABLE语句确实是分区表做增量更新的最优选择，这种更新方式逻辑清晰简单，实现方式优雅，绝对是不二之选。
5，更新后全量表HDFS分区的目录情况
更新后全量表HDFS分区的目录情况
可以看到，在HDFS目录中，语句执行成功后，自动创建了新增的4条记录所对应的分区。
6，总结
之前一直苦于在HIVE不开启事务的模式下，怎么做增量更新。
刚接触hive，思维还停留在传统的关系型数据库中，对不能DELETE，UPDATE操作的数仓方式非常不适应，对这种无法更新数据行的数仓深感蛋疼（认识还处于低级水平所致）。经过这番探索后发现，其实hive远比自己想的要强大的多，一般常规性的问题，前人早已给出解决方案，自己的困惑完全是来自于低级的无知。
上面的这个例子中，如果有数据库日志更新表或原表中有一个可用的update_time时间戳，t1数据集其实可以在sqoop中的query选项使用，导入HDFS后生成一个临时表，然后直接用这个临时表insert overwrite table到目标全量表。
完。
