hive SQL优化之distribute by和sort by .

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 最近在优化hiveSQL，

下面是一段排序，分组后取每组第一行记录的SQL

INSERT OVERWRITE TABLE t_wa_funnel_distinct_temp PARTITION (pt='${SRCTIME}')
SELECT
    bussiness_id,
    cookie_id,
    session_id,
    funnel_id,
    group_first(funnel_name) funnel_name,
    step_id,
    group_first(step_name) step_name,
    group_first(log_type) log_type,
    group_first(url_pattern) url_pattern,
    group_first(url) url,
    group_first(refer) refer,
    group_first(log_time) log_time,
    group_first(is_new_visitor) is_new_visitor,
    group_first(is_mobile_traffic) is_mobile_traffic,
    group_first(is_bounce) is_bounce,
    group_first(campaign_name) campaign_name,
    group_first(group_name) group_name,
    group_first(slot_name) slot_name,
    group_first(source_type) source_type,
    group_first(next_page) next_page,
    group_first(continent) continent,
    group_first(sub_continent_region) sub_continent_region,
    group_first(country) country,
    group_first(region) region,
    group_first(city) city,
    group_first(language) language,
    group_first(browser) browser,
    group_first(os) os,
    group_first(screen_color) screen_color,
    group_first(screen_resolution) screen_resolution,
    group_first(flash_version) flash_version,
    group_first(java) java,
    group_first(host) host
FROM
(   SELECT *
    FROM r_wa_funnel
    WHERE pt='${SRCTIME}'
    ORDER BY bussiness_id, cookie_id, session_id, funnel_id, step_id, log_time ASC
) t1
GROUP BY pt, bussiness_id, cookie_id, session_id, funnel_id, step_id;

group_first: 自定义函数， 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

下面在hive上以SRCTIME = 2011.11.01.21 执行以上SQL. 2011.11.01.21 小时分区记录数有10435486

执行时间:

从上面可以看出，reduce阶段只有一个reduce， 这是因为ORDER BY是全局排序，hive只能通过一个reduce进行排序
从业务需求来看， 只要按bussiness_id, cookie_id, session_id, funnel_id, step_id分组，组内按
log_time升序排序即可.

OK, 这样可以采用hive提供的distribute by 和 sort by, 这样可以充分利用hadoop资源， 在多个
reduce中局部按log_time 排序

优化有的hive代码:

INSERT OVERWRITE TABLE t_wa_funnel_distinct PARTITION (pt='2011.11.01.21')
SELECT
    bussiness_id,
    cookie_id,
    session_id,
    funnel_id,
    group_first(funnel_name) funnel_name,
    step_id,
    group_first(step_name) step_name,
    group_first(log_type) log_type,
    group_first(url_pattern) url_pattern,
    group_first(url) url,
    group_first(refer) refer,
    group_first(log_time) log_time,
    group_first(is_new_visitor) is_new_visitor,
    group_first(is_mobile_traffic) is_mobile_traffic,
    group_first(is_bounce) is_bounce,
    group_first(campaign_name) campaign_name,
    group_first(group_name) group_name,
    group_first(slot_name) slot_name,
    group_first(source_type) source_type,
    group_first(next_page) next_page,
    group_first(continent) continent,
    group_first(sub_continent_region) sub_continent_region,
    group_first(country) country,
    group_first(region) region,
    group_first(city) city,
    group_first(language) language,
    group_first(browser) browser,
    group_first(os) os,
    group_first(screen_color) screen_color,
    group_first(screen_resolution) screen_resolution,
    group_first(flash_version) flash_version,
    group_first(java) java,
    group_first(host) host
FROM
(   SELECT *
    FROM r_wa_funnel
    WHERE pt='2011.11.01.21'
    distribute by bussiness_id, cookie_id, session_id, funnel_id, step_id sort by log_time ASC
) t1
GROUP BY bussiness_id, cookie_id, session_id, funnel_id, step_id;

执行时间:

第一个需要执行6:43， 而优化有只要执行0:35秒， 性能得到大幅提升

本文出自 “yyj0531” 博客，出处http://yaoyinjie.blog.51cto.com/3189782/703873