[
https://issues.apache.org/jira/browse/DRILL-6845?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16967216#comment-16967216
]
Boaz Ben-Zvi commented on DRILL-6845:
-------------------------------------
The same problem can also be addressed during plan time with the use of
statistics; see also DRILL-6949
> 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.
>
--
This message was sent by Atlassian Jira
(v8.3.4#803005)
