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https://issues.apache.org/jira/browse/IMPALA-8409?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Work on IMPALA-8409 started by Csaba Ringhofer.
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> STRINGs without stats have too low row-size in explain plan
> -----------------------------------------------------------
>
> Key: IMPALA-8409
> URL: https://issues.apache.org/jira/browse/IMPALA-8409
> Project: IMPALA
> Issue Type: Bug
> Components: Frontend
> Affects Versions: Impala 3.2.0
> Reporter: Csaba Ringhofer
> Assignee: Csaba Ringhofer
> Priority: Minor
> Labels: explain, statistics
>
> STRING columns without avg_size statistic are calculated into the row-size as
> 11 bytes, while they take 12 bytes in the tuple (+ more somewhere in the
> memory if they are not empty). The issue is caused by adding -1 (meaning
> unknown) to the 12 byte slot size.
> I think that this doesn't cause problems, as the estimation is probably way
> off without statistics anyway, but row-size >= tuple size seems like a
> meaningful invariant that we shouldn't break.
> Reproduce:
> {code}
> create table test_row_size (s string);
> explain select * from test_row_size;
> Result:
> ...
> WARNING: The following tables are missing relevant table and/or column
> statistics.
> default.test_row_size
> ...
> 00:SCAN HDFS [default.test_row_size]
> partitions=1/1 files=0 size=0B
> row-size=11B cardinality=0
> {code}
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