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Posted to issues@drill.apache.org by "Arina Ielchiieva (Jira)" <ji...@apache.org> on 2019/11/04 12:40:00 UTC

[jira] [Updated] (DRILL-6845) Eliminate duplicates for Semi Hash Join

     [ https://issues.apache.org/jira/browse/DRILL-6845?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Arina Ielchiieva updated DRILL-6845:
------------------------------------
    Fix Version/s:     (was: 1.17.0)

> Eliminate duplicates for Semi Hash Join
> ---------------------------------------
>
>                 Key: DRILL-6845
>                 URL: https://issues.apache.org/jira/browse/DRILL-6845
>             Project: Apache Drill
>          Issue Type: Improvement
>          Components: Execution - Relational Operators
>    Affects Versions: 1.14.0
>            Reporter: Boaz Ben-Zvi
>            Assignee: Boaz Ben-Zvi
>            Priority: Minor
>
> Following DRILL-6735: The performance of the new Semi Hash Join may degrade if the build side contains excessive number of join-key duplicate rows; this mainly a result of the need to store all those rows first, before the hash table is built.
>   Proposed solution: For Semi, the Hash Agg would create a Hash-Table initially, and use it to eliminate key-duplicate rows as they arrive.
>   Proposed extra: That Hash-Table has an added cost (e.g. resizing). So perform "runtime stats" – Check initial number of incoming rows (e.g. 32k), and if the number of duplicates is less than some threshold (e.g. %20) – cancel that "early" hash table.
>  



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