Details
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Bug
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Status: Closed
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Critical
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Resolution: Fixed
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0.6.0
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None
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ppd
Description
Query is over-optimized by PPD when sub-queries have the same alias name, see the query:
-------------------------------
create table if not exists dm_fact_buyer_prd_info_d (
category_id string
,gmv_trade_num int
,user_id int
)
PARTITIONED BY (ds int);
set hive.optimize.ppd=true;
set hive.map.aggr=true;
explain select category_id1,category_id2,assoc_idx
from (
select
category_id1
, category_id2
, count(distinct user_id) as assoc_idx
from (
select
t1.category_id as category_id1
, t2.category_id as category_id2
, t1.user_id
from (
select category_id, user_id
from dm_fact_buyer_prd_info_d
group by category_id, user_id ) t1
join (
select category_id, user_id
from dm_fact_buyer_prd_info_d
group by category_id, user_id ) t2 on t1.user_id=t2.user_id
) t1
group by category_id1, category_id2 ) t_o
where category_id1 <> category_id2
and assoc_idx > 2;
-----------------------------
The query above will fail when execute, throwing exception: "can not cast UDFOpNotEqual(Text, IntWritable) to UDFOpNotEqual(Text, Text)".
I explained the query and the execute plan looks really wired ( only Stage-1, see the highlighted predicate):
-------------------------------
Stage: Stage-1
Map Reduce
Alias -> Map Operator Tree:
t_o:t1:t1:dm_fact_buyer_prd_info_d
TableScan
alias: dm_fact_buyer_prd_info_d
Filter Operator
predicate:
expr: (category_id <> user_id)
type: boolean
Select Operator
expressions:
expr: category_id
type: string
expr: user_id
type: bigint
outputColumnNames: category_id, user_id
Group By Operator
keys:
expr: category_id
type: string
expr: user_id
type: bigint
mode: hash
outputColumnNames: _col0, _col1
Reduce Output Operator
key expressions:
expr: _col0
type: string
expr: _col1
type: bigint
sort order: ++
Map-reduce partition columns:
expr: _col0
type: string
expr: _col1
type: bigint
tag: -1
Reduce Operator Tree:
Group By Operator
keys:
expr: KEY._col0
type: string
expr: KEY._col1
type: bigint
mode: mergepartial
outputColumnNames: _col0, _col1
Select Operator
expressions:
expr: _col0
type: string
expr: _col1
type: bigint
outputColumnNames: _col0, _col1
File Output Operator
compressed: true
GlobalTableId: 0
table:
input format: org.apache.hadoop.mapred.SequenceFileInputFormat
output format: org.apache.hadoop.hive.ql.io.HiveSequenceFileOutputFormat
----------------------------------
If disabling predicate push down (set hive.optimize.ppd=true), the error is gone; I tried disabling map side aggregate, the error is gone,too.
Changing the alias of subquery 't1' (either the inner one or the join result), the bug disappears, too.
