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https://issues.apache.org/jira/browse/IMPALA-10785?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17384435#comment-17384435
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Qifan Chen commented on IMPALA-10785:
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For 3), SlotDescriptor in FE has the field called isNullable_
(https://github.com/apache/impala/blob/master/fe/src/main/java/org/apache/impala/analysis/SlotDescriptor.java#L66).
Seems isNullable_ of the union should be set to isNullable_ field of the column
in the hdfs table when that for the corresponding column in the kudu table is
false (not nullable).
> when union kudu table and hdfs table, union passthrough does not take effect
> ----------------------------------------------------------------------------
>
> Key: IMPALA-10785
> URL: https://issues.apache.org/jira/browse/IMPALA-10785
> Project: IMPALA
> Issue Type: Improvement
> Reporter: pengdou1990
> Priority: Major
>
> IMPALA-3586 already supports union passthrough, and brings great performance
> improvements in union， but there is still some problems when union between
> hdfs table and kudu table ，several points cause the problem:
> # in kudu scanner node output TupleDescriptor, string slot is 16B,while in
> hdfs scanner node output TupleDescriptor, string slot is 12B,cause tuple
> memory layout mismatch
> # in kudu scanner node output TupleDescriptor, string slot is 16B, while in
> Union output TupleDescriptor, string slot is 12B,cause tuple memory layout
> mismatch
> # in Kudu Scannode, row key slot is not null, while in hdfs node, not null
> slot can't get from the metadata, cause tuple memory layout mismatch
> I hive resolved the 1st and 2nd points, how should I do with the 3rd point?
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