Vineet Garg created HIVE-21338:
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Summary: Remove order by and limit for aggregates
Key: HIVE-21338
URL: https://issues.apache.org/jira/browse/HIVE-21338
Project: Hive
Issue Type: Improvement
Components: Query Planning
Reporter: Vineet Garg
Assignee: Vineet Garg
If a query is guaranteed to produce at most one row LIMIT and ORDER BY could be
removed. This saves unnecessary vertex for LIMIT/ORDER BY.
{code:sql}
explain select count(*) cs from store_sales where ss_ext_sales_price > 100.00
order by cs limit 100
{code}
{code}
STAGE PLANS:
Stage: Stage-1
Tez
DagId: vgarg_20190227131959_2914830f-eab6-425d-b9f0-b8cb56f8a1e9:4
Edges:
Reducer 2 <- Map 1 (CUSTOM_SIMPLE_EDGE)
Reducer 3 <- Reducer 2 (SIMPLE_EDGE)
DagName: vgarg_20190227131959_2914830f-eab6-425d-b9f0-b8cb56f8a1e9:4
Vertices:
Map 1
Map Operator Tree:
TableScan
alias: store_sales
filterExpr: (ss_ext_sales_price > 100) (type: boolean)
Statistics: Num rows: 1 Data size: 112 Basic stats: COMPLETE
Column stats: NONE
Filter Operator
predicate: (ss_ext_sales_price > 100) (type: boolean)
Statistics: Num rows: 1 Data size: 112 Basic stats:
COMPLETE Column stats: NONE
Select Operator
Statistics: Num rows: 1 Data size: 112 Basic stats:
COMPLETE Column stats: NONE
Group By Operator
aggregations: count()
mode: hash
outputColumnNames: _col0
Statistics: Num rows: 1 Data size: 120 Basic stats:
COMPLETE Column stats: NONE
Reduce Output Operator
sort order:
Statistics: Num rows: 1 Data size: 120 Basic stats:
COMPLETE Column stats: NONE
value expressions: _col0 (type: bigint)
Execution mode: vectorized
Reducer 2
Execution mode: vectorized
Reduce Operator Tree:
Group By Operator
aggregations: count(VALUE._col0)
mode: mergepartial
outputColumnNames: _col0
Statistics: Num rows: 1 Data size: 120 Basic stats: COMPLETE
Column stats: NONE
Reduce Output Operator
key expressions: _col0 (type: bigint)
sort order: +
Statistics: Num rows: 1 Data size: 120 Basic stats: COMPLETE
Column stats: NONE
TopN Hash Memory Usage: 0.1
Reducer 3
Execution mode: vectorized
Reduce Operator Tree:
Select Operator
expressions: KEY.reducesinkkey0 (type: bigint)
outputColumnNames: _col0
Statistics: Num rows: 1 Data size: 120 Basic stats: COMPLETE
Column stats: NONE
Limit
Number of rows: 100
Statistics: Num rows: 1 Data size: 120 Basic stats: COMPLETE
Column stats: NONE
File Output Operator
compressed: false
Statistics: Num rows: 1 Data size: 120 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: 100
Processor Tree:
ListSink
{code}
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