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https://issues.apache.org/jira/browse/HIVE-22363?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16957011#comment-16957011
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Zoltan Haindrich commented on HIVE-22363:
-----------------------------------------
for a detection of something like this:
{code}
pRS-pGBY-cRS-cGBY
{code}
the problematic case was something like this:
{code}
pRS-pGBY-FIL-cRS-cGBY
{code}
note that it also accepted cases like:
{code}
pRS-xGBY-pGBY-cRS-cGBY
{code}
> ReduceDeduplication may leave an invalid GroupByOperator behind in some cases
> -----------------------------------------------------------------------------
>
> Key: HIVE-22363
> URL: https://issues.apache.org/jira/browse/HIVE-22363
> Project: Hive
> Issue Type: Bug
> Components: Physical Optimizer
> Affects Versions: 3.1.2
> Reporter: Zoltan Haindrich
> Assignee: Zoltan Haindrich
> Priority: Major
> Labels: pull-request-available
> Attachments: HIVE-22363.01.patch, HIVE-22363.02.patch,
> HIVE-22363.03.patch
>
> Time Spent: 0.5h
> Remaining Estimate: 0h
>
> since HIVE-11387 reducededup may traverse {{GroupByOperators}} [as
> well|https://github.com/apache/hive/blob/c6626edb65c2cd00576647e54db1995628fe64da/ql/src/java/org/apache/hadoop/hive/ql/optimizer/correlation/CorrelationUtilities.java#L244]
> But the removal logic only removes the first parent; so if there is some
> other operator (a FIL in this case) between the sink and the gby - the
> removal may not happen
> [here|https://github.com/apache/hive/blob/c6626edb65c2cd00576647e54db1995628fe64da/ql/src/java/org/apache/hadoop/hive/ql/optimizer/correlation/CorrelationUtilities.java#L458]
> {code}
> set hive.cbo.enable=false;
> drop table if exists xl1;
> create table xl1 as
> select '1' as mdl_yr_desc, 2 as seq_no,'3' as opt_desc1,4 as opt_desc,1 as
> row_num;
> explain
> select trim(base.mdl_yr_desc) mdl_yr_desc, trim(base.opt_desc) opt_desc
> from
> (
> SELECT trim(mdl_yr_desc) mdl_yr_desc, concat_ws(' ',
> collect_set(trim(opt_desc1))) AS opt_desc
> from
> (
> select t14304.*
> from
> (
> select * from xl1
> ) t14304
> where row_num = 1
> order by trim(mdl_yr_desc), cast(seq_no as int) asc
> ) x
> group by trim(mdl_yr_desc)
> ) base
> inner join
> (
> select 1 as v
> ) dedup
> on trim(base.mdl_yr_desc) != dedup.v
> group by trim(base.mdl_yr_desc), trim(base.opt_desc) ;
> {code}
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