[jira] [Commented] (HIVE-19097) related equals and in operators may cause inaccurate stats estimations

["Zoltan Haindrich (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-19097?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16423923#comment-16423923 ] 

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

I currently see 2 possible ways to fix this...
* a calcite rule might "notice" and simplify {{c in (X,A,B,C) and c=X}} to {{c=X}} ; [~jcamachorodriguez]: would it be hard to implement something like this?
* ensure that stats are overestimating: keep track of the used columns so far during Stats calculation - and skip calculation if it relates to an earlier one

> 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
>            Priority: Major
>
> 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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