1、查看執行計劃方法
語法:explain [extended] Hiveql;
/*例子:*/
explain select count(distinct mobilename) from testtab_small;
2、執行計劃基本要素
- 主要步驟及依賴關係,從上到下
- 各主要步驟關鍵信息,包括:
關鍵信息 | 關鍵字 | 說明 |
---|---|---|
Map或reduce操作 | Map Operator Tree、Reduce Operator Tree | map、reduce階段 |
掃描表 | TableScan | 要查詢的表 |
表數據量統計 | Statistics | 包括行數、數據大小 |
查詢算子 | Select Operator | 要檢索的字段 |
分區算子 | Group By Operator | 聚合如count()等需要 |
排序 | sort order | 是否排序,+表排序,空不排序 |
是否本地任務 | Local Work、Local Tables、Map Local Operator Tree | 見於Map端的連接,有小表參與連接、且auto.convert.join=true |
連接算子 | Join Operator | 連接 |
連接條件 | condition map | 連接條件:Left Outer Join0 to 1 |
2、explain select count(distinct mobilename) from testtab_small
完整的執行計劃示例。之後的主要體現差異,不是全部,比如刪除Stage0部分。
/*整體步驟,從上往下看*/
STAGE DEPENDENCIES:
Stage-1 is a root stage
Stage-0 depends on stages: Stage-1
STAGE PLANS:
Stage: Stage-1
Map Reduce
Map Operator Tree:
/*掃描的表*/
TableScan
alias: testtab_small
/*表數據量統計,13條,629字節?*/
Statistics: Num rows: 13 Data size: 629 Basic stats: COMPLETE Column stats: NONE
Select Operator
/*檢索的字段是mobilename*/
expressions: mobilename (type: string)
outputColumnNames: mobilename
Statistics: Num rows: 13 Data size: 629 Basic stats: COMPLETE Column stats: NONE
Group By Operator
/*聚合操作*/
aggregations: count(DISTINCT mobilename)
keys: mobilename (type: string)
mode: hash
outputColumnNames: _col0, _col1
Statistics: Num rows: 13 Data size: 629 Basic stats: COMPLETE Column stats: NONE
Reduce Output Operator
key expressions: _col0 (type: string)
/*+ 需要排序*/
sort order: +
Statistics: Num rows: 13 Data size: 629 Basic stats: COMPLETE Column stats: NONE
Reduce Operator Tree:
Group By Operator
aggregations: count(DISTINCT KEY._col0:0._col0)
mode: mergepartial
outputColumnNames: _col0
Statistics: Num rows: 1 Data size: 16 Basic stats: COMPLETE Column stats: NONE
File Output Operator
compressed: false
Statistics: Num rows: 1 Data size: 16 Basic stats: COMPLETE Column stats: NONE
table:
input format: org.apache.hadoop.mapred.SequenceFileInputFormat
output format: org.apache.hadoop.hive.ql.io.HiveSequenceFileOutputFormat
serde: org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe
Stage: Stage-0
Fetch Operator
limit: -1
Processor Tree:
ListSink
3、explain select count(mobilename) from testtab_small;
Stage: Stage-1
Map Reduce
Map Operator Tree:
TableScan
alias: testtab_small
Statistics: Num rows: 13 Data size: 629 Basic stats: COMPLETE Column stats: NONE
Select Operator
expressions: mobilename (type: string)
outputColumnNames: mobilename
Statistics: Num rows: 13 Data size: 629 Basic stats: COMPLETE Column stats: NONE
Group By Operator
aggregations: count(mobilename)
mode: hash
outputColumnNames: _col0
Statistics: Num rows: 1 Data size: 8 Basic stats: COMPLETE Column stats: NONE
Reduce Output Operator
sort order:
Statistics: Num rows: 1 Data size: 8 Basic stats: COMPLETE Column stats: NONE
value expressions: _col0 (type: bigint)
Reduce Operator Tree:
Group By Operator
aggregations: count(VALUE._col0)
mode: mergepartial
outputColumnNames: _col0
Statistics: Num rows: 1 Data size: 8 Basic stats: COMPLETE Column stats: NONE
File Output Operator
compressed: false
Statistics: Num rows: 1 Data size: 8 Basic stats: COMPLETE Column stats: NONE
table:
input format: org.apache.hadoop.mapred.SequenceFileInputFormat
output format: org.apache.hadoop.hive.ql.io.HiveSequenceFileOutputFormat
serde: org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe
4、全局排序
explain select * from testtab_small order by mobilename;
- 無聚合算子
- 在Map Operator Tree下的Reduce Output Operator下就有排序了(sort order: +)
Stage: Stage-1
Map Reduce
Map Operator Tree:
TableScan
alias: testtab_small
Statistics: Num rows: 13 Data size: 629 Basic stats: COMPLETE Column stats: NONE
Select Operator
expressions: mobilename (type: string), testrecordid (type: string)
outputColumnNames: _col0, _col1
Statistics: Num rows: 13 Data size: 629 Basic stats: COMPLETE Column stats: NONE
Reduce Output Operator
key expressions: _col0 (type: string)
sort order: +
Statistics: Num rows: 13 Data size: 629 Basic stats: COMPLETE Column stats: NONE
value expressions: _col1 (type: string)
Reduce Operator Tree:
Select Operator
expressions: KEY.reducesinkkey0 (type: string), VALUE._col0 (type: string)
outputColumnNames: _col0, _col1
Statistics: Num rows: 13 Data size: 629 Basic stats: COMPLETE Column stats: NONE
File Output Operator
compressed: false
Statistics: Num rows: 13 Data size: 629 Basic stats: COMPLETE Column stats: NONE
table:
input format: org.apache.hadoop.mapred.SequenceFileInputFormat
output format: org.apache.hadoop.hive.ql.io.HiveSequenceFileOutputFormat
serde: org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe
5、關聯小表,Map端連接
hive.auto.convert.join=true /默認值/
hive> explain select a.testrecordid,a.mobilename,b.mobilename from testtab_small a left join testtab_small2 b on a.testrecordid=b.testrecordid;
- 總步驟增至3個
- 多了本地任務,Map Reduce Local Work。即hadoop的分佈式緩存技術
- Map Join Operator
STAGE DEPENDENCIES:
Stage-4 is a root stage
Stage-3 depends on stages: Stage-4
Stage-0 depends on stages: Stage-3
STAGE PLANS:
Stage: Stage-4
Map Reduce Local Work
Alias -> Map Local Tables:
$hdt$_1:b
Fetch Operator
limit: -1
Alias -> Map Local Operator Tree:
$hdt$_1:b
TableScan
alias: b
Statistics: Num rows: 13 Data size: 655 Basic stats: COMPLETE Column stats: NONE
Select Operator
expressions: mobilename (type: string), testrecordid (type: string)
outputColumnNames: _col0, _col1
Statistics: Num rows: 13 Data size: 655 Basic stats: COMPLETE Column stats: NONE
HashTable Sink Operator
keys:
0 _col1 (type: string)
1 _col1 (type: string)
Stage: Stage-3
Map Reduce
Map Operator Tree:
TableScan
alias: a
Statistics: Num rows: 13 Data size: 629 Basic stats: COMPLETE Column stats: NONE
Select Operator
expressions: mobilename (type: string), testrecordid (type: string)
outputColumnNames: _col0, _col1
Statistics: Num rows: 13 Data size: 629 Basic stats: COMPLETE Column stats: NONE
Map Join Operator
condition map:
Left Outer Join0 to 1
keys:
0 _col1 (type: string)
1 _col1 (type: string)
outputColumnNames: _col0, _col1, _col2
Statistics: Num rows: 14 Data size: 691 Basic stats: COMPLETE Column stats: NONE
Select Operator
expressions: _col1 (type: string), _col0 (type: string), _col2 (type: string)
outputColumnNames: _col0, _col1, _col2
Statistics: Num rows: 14 Data size: 691 Basic stats: COMPLETE Column stats: NONE
File Output Operator
compressed: false
Statistics: Num rows: 14 Data size: 691 Basic stats: COMPLETE Column stats: NONE
table:
input format: org.apache.hadoop.mapred.SequenceFileInputFormat
output format: org.apache.hadoop.hive.ql.io.HiveSequenceFileOutputFormat
serde: org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe
Local Work:
Map Reduce Local Work
6、Reduce端連接
hive.auto.convert.join=false
與5相同的語句,Reduce端連接執行計劃:
- Map Operator Tree裏有2個評級的TableScan,對應Mapper多個數據來源
- Reduce Operator Tree下Join Operator:reduce端連接。
STAGE PLANS:
Stage: Stage-1
Map Reduce
Map Operator Tree:
TableScan
alias: a
Statistics: Num rows: 13 Data size: 629 Basic stats: COMPLETE Column stats: NONE
Select Operator
expressions: mobilename (type: string), testrecordid (type: string)
outputColumnNames: _col0, _col1
Statistics: Num rows: 13 Data size: 629 Basic stats: COMPLETE Column stats: NONE
Reduce Output Operator
key expressions: _col1 (type: string)
sort order: +
Map-reduce partition columns: _col1 (type: string)
Statistics: Num rows: 13 Data size: 629 Basic stats: COMPLETE Column stats: NONE
value expressions: _col0 (type: string)
TableScan
alias: b
Statistics: Num rows: 13 Data size: 655 Basic stats: COMPLETE Column stats: NONE
Select Operator
expressions: mobilename (type: string), testrecordid (type: string)
outputColumnNames: _col0, _col1
Statistics: Num rows: 13 Data size: 655 Basic stats: COMPLETE Column stats: NONE
Reduce Output Operator
key expressions: _col1 (type: string)
sort order: +
Map-reduce partition columns: _col1 (type: string)
Statistics: Num rows: 13 Data size: 655 Basic stats: COMPLETE Column stats: NONE
value expressions: _col0 (type: string)
Reduce Operator Tree:
Join Operator
condition map:
Left Outer Join0 to 1
keys:
0 _col1 (type: string)
1 _col1 (type: string)
outputColumnNames: _col0, _col1, _col2
Statistics: Num rows: 14 Data size: 691 Basic stats: COMPLETE Column stats: NONE
Select Operator
expressions: _col1 (type: string), _col0 (type: string), _col2 (type: string)
outputColumnNames: _col0, _col1, _col2
Statistics: Num rows: 14 Data size: 691 Basic stats: COMPLETE Column stats: NONE
File Output Operator
compressed: false
Statistics: Num rows: 14 Data size: 691 Basic stats: COMPLETE Column stats: NONE
table:
input format: org.apache.hadoop.mapred.SequenceFileInputFormat
output format: org.apache.hadoop.hive.ql.io.HiveSequenceFileOutputFormat
serde: org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe