[jira] [Work started] (IMPALA-8409) STRINGs without stats have too low row-size in explain plan

["Csaba Ringhofer (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/IMPALA-8409?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Work on IMPALA-8409 started by Csaba Ringhofer.
-----------------------------------------------
> 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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