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https://issues.apache.org/jira/browse/HIVE-948?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13580784#comment-13580784
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Ashutosh Chauhan commented on HIVE-948:
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New file NonBlockingOpDedup.java is not in phabricator, so commenting here:
// updates schema only (this should be the last optimizer modifying operator
tree)
+ pSEL.setSchema(cSEL.getSchema());
+ }
* Why this needs to be last optimizer? Please add more comments for the reason
for that. Even if it is, currently in Optimizer.java it is not.
* Also, parent should always have child's schema, isnt it? If so, why you have
it in within if () block.
+
+ pSEL.getConf().setSelectStar(cSEL.getConf().isSelectStar());
* Shouldn't parent be selectStar either when child is select-star or parent
itself is select-star. e.g, SEL(sel-star)-SEL(no-sel-star). So, this should be
pSEL.getConf().setSelectStar(cSEL.getConf().isSelectStar() ||
pSEL.getConf().isSelectStar()); If not, please add comments for it, since it
wasn't obvious.
> more query plan optimization rules
> -----------------------------------
>
> Key: HIVE-948
> URL: https://issues.apache.org/jira/browse/HIVE-948
> Project: Hive
> Issue Type: Improvement
> Reporter: Ning Zhang
> Assignee: Navis
> Attachments: HIVE-948.D8463.1.patch, HIVE-948.D8463.2.patch,
> HIVE-948.D8463.3.patch, HIVE-948.D8463.3.patch
>
>
> Many query plans are not optimal in that they contain redundant operators.
> Some examples are unnecessary select operators (select followed by select,
> select output being the same as input etc.). Even though these operators are
> not very expensive, they could account for around 10% of CPU time in some
> simple queries. It seems they are low-hanging fruits that we should pick
> first.
> BTW, it seems these optimization rules should be added at the last stage of
> the physical optimization phase since some redundant operators are added to
> facilitate physical plan generation.
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