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https://issues.apache.org/jira/browse/IMPALA-13411?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17890754#comment-17890754
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ASF subversion and git services commented on IMPALA-13411:
----------------------------------------------------------
Commit f5a8771a982cb270bbd7bce8e8253198c35c5ab4 in impala's branch
refs/heads/master from Yida Wu
[ https://gitbox.apache.org/repos/asf?p=impala.git;h=f5a8771a9 ]
IMPALA-13411: Fix DCHECK fires for scan nodes that produce zero-length tuples
Removed the DCHECK assertion that tuple_data_len must be greater
than zero in tuple-file-writer.cc and tuple-file-reader.cc,
because in certain cases, such as count(*), tuple_data_len can
be zero, as no column data is returned and only the row count
matters.
Tests:
Adds TestTupleCacheCountStar for the regression test.
Change-Id: I264b537f0eb678b65081e90c21726198f254513d
Reviewed-on: http://gerrit.cloudera.org:8080/21953
Reviewed-by: Impala Public Jenkins <[email protected]>
Tested-by: Impala Public Jenkins <[email protected]>
> DCHECK can fire for scan nodes that produce zero-length tuples
> --------------------------------------------------------------
>
> Key: IMPALA-13411
> URL: https://issues.apache.org/jira/browse/IMPALA-13411
> Project: IMPALA
> Issue Type: Bug
> Components: Backend
> Affects Versions: Impala 4.5.0
> Reporter: Joe McDonnell
> Assignee: Michael Smith
> Priority: Major
>
> This query crashes when using the tuple cache:
> {noformat}
> select count(*) from functional.alltypes;{noformat}
> It hits this assert:
> [https://github.com/apache/impala/blob/6121c4f7d61fb9f2341cf14e1be3404325fb35b9/be/src/exec/tuple-file-writer.cc#L105]
> {noformat}
> DCHECK_GT(tuple_data_len, 0);{noformat}
> For this count(*) query, it is not actually returning any columns. Instead,
> only the row count matters and the count does not require any tuple data. So,
> the tuple data is empty.
> We can revisit this DCHECK and either remove it or modify the condition to
> check if the tuple size is zero.
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