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From "Zoltan Haindrich (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-19097) related equals and in operators may cause inaccurate stats estimations
Date Mon, 09 Apr 2018 15:20:00 GMT

    [ https://issues.apache.org/jira/browse/HIVE-19097?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16430713#comment-16430713
] 

Zoltan Haindrich commented on HIVE-19097:
-----------------------------------------

[~jcamachorodriguez] I've taken a look at HivePointLookupOptimizerRule.java ; I think it would
be better to place my IN opener there...because that's also a calcite rule; I don't really
need to do any modifications ; however the change still doesn't worth that much - even thru
the in is now gone; I think there is no rule which could simplify  ((a=1 || b=2) &&
a=1) to (a=1)...or I missed it :)

> related equals and in operators may cause inaccurate stats estimations
> ----------------------------------------------------------------------
>
>                 Key: HIVE-19097
>                 URL: https://issues.apache.org/jira/browse/HIVE-19097
>             Project: Hive
>          Issue Type: Bug
>            Reporter: Zoltan Haindrich
>            Assignee: Zoltan Haindrich
>            Priority: Major
>         Attachments: HIVE-19097.01.patch
>
>
> tpcds#74 is optimized in a way that for date_dim the condition contains IN and = for
the same column
> {code:java}
> |             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}
> the "real" row count will be 365
> for separate {{IN}} and {{=}} the estimation is very good; but if both are present it
becomes (very) underestimated.
> {code:java}
> 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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