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https://issues.apache.org/jira/browse/HIVE-17193?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16215590#comment-16215590
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Sahil Takiar commented on HIVE-17193:
-------------------------------------
{quote} The drawback is we'll lose some optimization opportunities - actually
I'm not sure whether it's possible that two target map works share the same DPP
in current implementation. {quote} As far as I know, this isn't possible. A DPP
subtree can only be used to prune a single target {{MapWork}} - although that
is something we want to change in HIVE-17178
{quote} Two DPP works can be considered equivalent as long as they output same
records. {quote} I'm not sure how this would work, you don't know what a DPP
work will output until the query actually starts to run.
I think a good fix here would to be just implement HIVE-17178 (I'm not sure,
but this may be the same as HIVE-17877). If two DPP sinks are completely
equivalent (same source table, filters, operations, etc.), but they only differ
by the value of {{Target Work}}, then I think we should be able to combine them
into a single DPP tree, with multiple target works. The value of the target
work shouldn't change the value of the data that is written by a DPP subtree,
so if the subtrees are equivalent, we can combine them. The main work will be
to change the DPP code so that there can be multiple Target Works.
> HoS: don't combine map works that are targets of different DPPs
> ---------------------------------------------------------------
>
> Key: HIVE-17193
> URL: https://issues.apache.org/jira/browse/HIVE-17193
> Project: Hive
> Issue Type: Bug
> Reporter: Rui Li
> Assignee: Rui Li
>
> Suppose {{srcpart}} is partitioned by {{ds}}. The following query can trigger
> the issue:
> {code}
> explain
> select * from
> (select srcpart.ds,srcpart.key from srcpart join src on srcpart.ds=src.key)
> a
> join
> (select srcpart.ds,srcpart.key from srcpart join src on
> srcpart.ds=src.value) b
> on a.key=b.key;
> {code}
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