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Posted to dev@hive.apache.org by "Zoltan Haindrich (JIRA)" <ji...@apache.org> on 2018/04/03 11:46:00 UTC
[jira] [Created] (HIVE-19097) related equals and in operators may
result in a high inaccurate stat estimation
Zoltan Haindrich created HIVE-19097:
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Summary: related equals and in operators may result in a high inaccurate stat estimation
Key: HIVE-19097
URL: https://issues.apache.org/jira/browse/HIVE-19097
Project: Hive
Issue Type: Bug
Reporter: Zoltan Haindrich
tpcds#74 is optimized in a way that for date_dim the condition contains IN and = for the same column
{code}
| Map Operator Tree: |
| TableScan |
| alias: date_dim |
| filterExpr: (((d_year) IN (2001, 2002) and (d_year = 2002) and d_date_sk is not null) or ((d_year) IN (2001, 2002) and (d_year = 2001) and d_date_sk is not null)) (type: boolean) |
| Statistics: Num rows: 73049 Data size: 876588 Basic stats: COMPLETE Column stats: COMPLETE |
| Filter Operator |
| predicate: ((d_year) IN (2001, 2002) and (d_year = 2002) and d_date_sk is not null) (type: boolean) |
| Statistics: Num rows: 4 Data size: 48 Basic stats: COMPLETE Column stats: COMPLETE |
{code}
for separate {{IN}} and {{=}} the estimation is very good; but if both are present it becomes (very) underestimated.
{code}
set hive.query.results.cache.enabled=false;
drop table if exists t1;
drop table if exists t8;
create table t1 (a integer,b integer);
create table t8 like t1;
insert into t1 values (1,1),(2,2),(3,3),(4,4),(5,5);
insert into t8
select * from t1 union all select * from t1 union all select * from t1 union all select * from t1 union all
select * from t1 union all select * from t1 union all select * from t1 union all select * from t1
;
analyze table t1 compute statistics for columns;
analyze table t8 compute statistics for columns;
explain analyze select sum(a) from t8 where b in (2,3) group by b;
explain analyze select sum(a) from t8 where b=2 group by b;
explain analyze select sum(a) from t1 where b in (2,3) and b=2 group by b;
explain analyze select sum(a) from t8 where b in (2,3) and b=2 group by b;
{code}
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