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处理Hive中的数据倾斜的方法

发布者: Error | 发布时间: 2025-6-20 09:03| 查看数: 105| 评论数: 0|帖子模式

1 groupby(大表分组-局部聚合+全局聚合)

示例1：

select label,sum(cnt) as all from
(
select rd,label,sum(1) as cnt from
(
select id,label,round(rand(),2) as rd,value from tmp1
) as tmp
group by rd,label
) as tmp
group by label;

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示例2：

select
split(new_source,'\\_')[0] as source
,sum(cnt) as cnt
from
(select
concat(source,'_', rand()*100) as new_source
,count(1) as cnt
from test_table
where day ='2022-01-01'
group by
concat(source,'_', rand()*100)
)tt
group by
split(new_source,'\\_')[0]

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2 join（大中表Join - 加salt + 小表膨胀）

示例1：

select label,sum(value) as all from
(
select rd,label,sum(value) as cnt from
(
select tmp1.rd as rd,tmp1.label as label,tmp1.value*tmp2.value as value
from
(
select id,round(rand(),1) as rd,label,value from tmp1
) as tmp1
join
(
select id,rd,label,value from tmp2
lateral view explode(split('0.0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9',',')) mytable as rd
) as tmp2
on tmp1.rd = tmp2.rd and tmp1.label = tmp2.label
) as tmp1
group by rd,label
) as tmp1
group by label;

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示例2：

select
source
,source_name
,sum(cnt) as cnt
from
(select
t1.source
,new_source
,nvl(source_name,'未知') as source_name
,count(imei) as cnt
from
(select
imei
,source
,concat(cast(rand()*10 as int ),'_',source ) as new_source
from test_table_1
where day ='2022-01-01'
) t1
inner join
(
select
source_name
,concat(preflix,'_',source) as new_source
from test_table_1
where day ='2022-01-01'
lateral view explode(split('0,1,2,3,4,5,6,7,8,9,10',','))b as preflix
) t2
on t1.new_source =t2.new_source
group by
t1.source
,new_source
,nvl(source_name,'未知')
) tta
group by
source
,source_name

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3 双大表Join - 抽样取倾斜key+BroadJoin

##优化前：
create table test.tmp_table_test_all as
select
imei
,lable_id
,nvl(label_name,'未知')
from tmp_table_1 t1
left join
(select
lable_id
,label_name
from tmp_table_2
where day ='2024-01-01') t2
on t1.lable_id =t2.lable_id
where t1.day ='2024-01-01'
;
## 优化后：
create table test.tmp_table_test_all_new as
with tmp_table_test_1 as
(select
lable_id
,count(1) as cnt
from tmp_table_1 t1
tablesample(5 percent) --抽样取5%的数据，减少table scan的量
group by lable_id
order by cnt desc
limit 100
)
select
imei
,lable_id
,nvl(label_name,'未知') as label_name
from tmp_table_1 t1
left join tmp_table_test_1 t2
on t1.lable_id =t2.lable_id
left join
(select
lable_id
,label_name
from tmp_table_2
where day ='2024-01-01') t3
on t1.lable_id =t3.lable_id
where t1.day ='2024-01-01' and t2.lable_id is null
union all
select
imei
,lable_id
,nvl(label_name,'未知') as label_name
from tmp_table_1 t1
inner join
(select
lable_id
from tmp_table_test_1 t1
left join tmp_table_2 t2
on t1.lable_id =t2.lable_id
where t2.day ='2024-01-01') t3
on t1.lable_id =t3.lable_id
where t1.day ='2024-01-01'
;

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4 小结

到此这篇关于处理Hive中的数据倾斜的方法的文章就介绍到这了,更多相关处理Hive数据倾斜内容请搜索脚本之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持脚本之家！

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处理Hive中的数据倾斜的方法

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