近期在优化hiveSQL。

以下是一段排序，分组后取每组第一行记录的SQL

1. INSERT OVERWRITE TABLE t_wa_funnel_distinct_temp PARTITION (pt='${SRCTIME}')
2. SELECT
3. bussiness_id,
4. cookie_id,
5. session_id,
6. funnel_id,
7. group_first(funnel_name) funnel_name,
8. step_id,
9. group_first(step_name) step_name,
10. group_first(log_type) log_type,
11. group_first(url_pattern) url_pattern,
12. group_first(url) url,
13. group_first(refer) refer,
14. group_first(log_time) log_time,
15. group_first(is_new_visitor) is_new_visitor,
16. group_first(is_mobile_traffic) is_mobile_traffic,
17. group_first(is_bounce) is_bounce,
18. group_first(campaign_name) campaign_name,
19. group_first(group_name) group_name,
20. group_first(slot_name) slot_name,
21. group_first(source_type) source_type,
22. group_first(next_page) next_page,
23. group_first(continent) continent,
24. group_first(sub_continent_region) sub_continent_region,
25. group_first(country) country,
26. group_first(region) region,
27. group_first(city) city,
28. group_first(language) language,
29. group_first(browser) browser,
30. group_first(os) os,
31. group_first(screen_color) screen_color,
32. group_first(screen_resolution) screen_resolution,
33. group_first(flash_version) flash_version,
34. group_first(java) java,
35. group_first(host) host
36. FROM
37. (   SELECT *
38. FROM r_wa_funnel
39. WHERE pt='${SRCTIME}'
40. ORDER BY bussiness_id, cookie_id, session_id, funnel_id, step_id, log_time ASC
41. ) t1
42. GROUP BY pt, bussiness_id, cookie_id, session_id, funnel_id, step_id;

group_first: 自己定义函数。用户取每组第一个字段

${SRCTIME}:
由外部oozie调度传入, 作为时间分区，精确到小时.eg: 2011.11.01.21



以下在hive上以SRCTIME = 2011.11.01.21
运行以上SQL. 2011.11.01.21小时分区记录数有10435486

运行时间:

从上面能够看出，reduce阶段仅仅有一个reduce， 这是由于ORDER BY是全局排序，hive仅仅能通过一个reduce进行排序

从业务需求来看， 仅仅要按bussiness_id, cookie_id, session_id, funnel_id, step_id分组，组内按

log_time升序排序就可以.



OK, 这样能够採用hive提供的distribute by 和 sort by,这样能够充分利用hadoop资源， 在多个

reduce中局部按log_time 排序



优化有的hive代码:

1. INSERT OVERWRITE TABLE t_wa_funnel_distinct PARTITION (pt='2011.11.01.21')
2. SELECT
3. bussiness_id,
4. cookie_id,
5. session_id,
6. funnel_id,
7. group_first(funnel_name) funnel_name,
8. step_id,
9. group_first(step_name) step_name,
10. group_first(log_type) log_type,
11. group_first(url_pattern) url_pattern,
12. group_first(url) url,
13. group_first(refer) refer,
14. group_first(log_time) log_time,
15. group_first(is_new_visitor) is_new_visitor,
16. group_first(is_mobile_traffic) is_mobile_traffic,
17. group_first(is_bounce) is_bounce,
18. group_first(campaign_name) campaign_name,
19. group_first(group_name) group_name,
20. group_first(slot_name) slot_name,
21. group_first(source_type) source_type,
22. group_first(next_page) next_page,
23. group_first(continent) continent,
24. group_first(sub_continent_region) sub_continent_region,
25. group_first(country) country,
26. group_first(region) region,
27. group_first(city) city,
28. group_first(language) language,
29. group_first(browser) browser,
30. group_first(os) os,
31. group_first(screen_color) screen_color,
32. group_first(screen_resolution) screen_resolution,
33. group_first(flash_version) flash_version,
34. group_first(java) java,
35. group_first(host) host
36. FROM
37. (   SELECT *
38. FROM r_wa_funnel
39. WHERE pt='2011.11.01.21'
40. distribute by bussiness_id, cookie_id, session_id, funnel_id, step_id sort by log_time ASC
41. ) t1
42. GROUP BY bussiness_id, cookie_id, session_id, funnel_id, step_id;

运行时间:

第一个须要运行6:43， 而优化有仅仅要运行0:35秒。性能得到大幅提升