[jira] [Work started] (IMPALA-8095) Detailed expression cardinality tests

["Paul Rogers (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/IMPALA-8095?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Work on IMPALA-8095 started by Paul Rogers.
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> Detailed expression cardinality tests
> -------------------------------------
>
>                 Key: IMPALA-8095
>                 URL: https://issues.apache.org/jira/browse/IMPALA-8095
>             Project: IMPALA
>          Issue Type: Improvement
>          Components: Frontend
>    Affects Versions: Impala 3.1.0
>            Reporter: Paul Rogers
>            Assignee: Paul Rogers
>            Priority: Minor
>
> Cardinality is a critical input to the query planning process, especially join planning. Impala has many high-level end-to-end tests that implicitly test cardinality at the "wholesale" level: A test will produce a wrong result if the cardinality is badly wrong.
> But, at present, no detailed unit tests exist for this topic. This ticket asks to add tests for:
> * Table cardinality, NDV values and null count in metadata retrieved from HMS.
> * Table cardinality, NDV values and null counts in metadata presented to the query.
> * Expression NDV and selectivity values (which derive from table cardinality and column NDV.)
> Since none of the existing "functional" tables provide the level of detail needed for these tests, add a new test table specifically for this task.



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