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這裏是我的蜂巢查詢蜂巢查詢執行計劃
Insert into schemaB.employee partition(year)
select * from schemaA.employee;
下面是這個查詢產生的查詢執行計劃。
hive> explain <query>;
STAGE DEPENDENCIES:
Stage-1 is a root stage
Stage-0 depends on stages: Stage-1
Stage-2 depends on stages: Stage-0
STAGE PLANS:
Stage: Stage-1
Map Reduce
Map Operator Tree:
TableScan
alias: employee
Statistics: Num rows: 65412411 Data size: 59121649936 Basic stats: COMPLETE Column stats: NONE
Select Operator
expressions: Col1 (type: binary), col2 (type: binary), col3 (type: array<string>), year (type: int)
outputColumnNames: _col0, _col1, _col2, _col3
Statistics: Num rows: 65412411 Data size: 59121649936 Basic stats: COMPLETE Column stats: NONE
Reduce Output Operator
key expressions: _col3 (type: int)
sort order: +
Map-reduce partition columns: _col3 (type: int)
Statistics: Num rows: 65412411 Data size: 59121649936 Basic stats: COMPLETE Column stats: NONE
value expressions: _col0 (type: binary), _col1 (type: binary), _col2 (type: array<string>), _col3 (type: int)
Reduce Operator Tree:
Extract
Statistics: Num rows: 65412411 Data size: 59121649936 Basic stats: COMPLETE Column stats: NONE
File Output Operator
compressed: true
Statistics: Num rows: 65412411 Data size: 59121649936 Basic stats: COMPLETE Column stats: NONE
table:
input format: org.apache.hadoop.hive.ql.io.orc.OrcInputFormat
output format: org.apache.hadoop.hive.ql.io.orc.OrcOutputFormat
serde: org.apache.hadoop.hive.ql.io.orc.OrcSerde
name: schemaB.employee
Stage: Stage-0
Move Operator
tables:
partition:
year
replace: false
table:
input format: org.apache.hadoop.hive.ql.io.orc.OrcInputFormat
output format: org.apache.hadoop.hive.ql.io.orc.OrcOutputFormat
serde: org.apache.hadoop.hive.ql.io.orc.OrcSerde
name: schemaB.employee
Stage: Stage-2
Stats-Aggr Operator
我有兩個相關的查詢執行計劃問題：
- 爲什麼會出現在查詢計劃減少一步？在我的理解中，它需要做的就是將數據從一個HDFS位置複製到另一個位置，這可以通過映射器單獨實現。減少步驟與表中存在的分區有關嗎？
- 什麼是統計彙總運算符步驟出現在第2階段？我無法找到相關文件解釋這一點。