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https://issues.apache.org/jira/browse/HIVE-8435?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14168829#comment-14168829
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Ashutosh Chauhan edited comment on HIVE-8435 at 10/12/14 10:52 PM:
-------------------------------------------------------------------
This optimization tries to remove SelectOperator from operator tree which
don't do any processing except forwarding columns from its parent to its
children.e.g.,
{code} select * from (select * from src where key = value) t1 join (select *
from src where key = value) t2;
{code}
Query tree
Without this optimization:
{noformat}
TS -> FIL -> SEL -> RS ->
JOIN -> SEL -> FS
TS -> FIL -> SEL -> RS ->
{noformat}
With this optimization
{noformat}
TS -> FIL -> RS ->
JOIN -> FS
TS -> FIL -> RS ->
{noformat}
Note absence of select operator after filter and after join operator.
was (Author: ashutoshc):
This optimization tries to remove SelectOperator from operator tree which
don't do any processing except forwarding columns from its parent to its
children.e.g.,
{code}
select * from (select * from src where key = value) t1 join (select * from src
where key = value) t2;
{code}
{noformat}
Query tree
Without this optimization:
TS -> FIL -> SEL -> RS ->
JOIN -> SEL -> FS
TS -> FIL -> SEL -> RS ->
With this optimization
TS -> FIL -> RS ->
JOIN -> FS
TS -> FIL -> RS ->
{noformat}
Note absence of select operator after filter and after join operator.
> Add identity project remover optimization
> -----------------------------------------
>
> Key: HIVE-8435
> URL: https://issues.apache.org/jira/browse/HIVE-8435
> Project: Hive
> Issue Type: New Feature
> Components: Logical Optimizer
> Affects Versions: 0.9.0, 0.10.0, 0.11.0, 0.12.0, 0.13.0
> Reporter: Ashutosh Chauhan
> Assignee: Ashutosh Chauhan
> Attachments: HIVE-8435.patch
>
>
> In some cases there is an identity project in plan which is useless. Better
> to optimize it away to avoid evaluating it without any benefit at runtime.
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