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https://issues.apache.org/jira/browse/HIVE-23716?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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mahesh kumar behera reassigned HIVE-23716:
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> Support Anti Join in Hive
> --------------------------
>
> Key: HIVE-23716
> URL: https://issues.apache.org/jira/browse/HIVE-23716
> Project: Hive
> Issue Type: Bug
> Reporter: mahesh kumar behera
> Assignee: mahesh kumar behera
> Priority: Major
>
> Currently hive does not support Anti join. The query for anti join is
> converted to left outer join and null filter on right side join key is added
> to get the desired result. This is causing
> # Extra computation — The left outer join projects the redundant columns
> from right side. Along with that, filtering is done to remove the redundant
> rows. This is can be avoided in case of anti join as anti join will project
> only the required columns and rows from the left side table.
> # Extra shuffle — In case of anti join the duplicate records moved to join
> node can be avoided from the child node. This can reduce significant amount
> of data movement if the number of distinct rows( join keys) is significant.
> # Extra Memory Usage - In case of map based anti join , hash set is
> sufficient as just the key is required to check if the records matches the
> join condition. In case of left join, we need the key and the non key columns
> also and thus a hash table will be required.
> For a query like
> {code:java}
> select wr_order_number FROM web_returns LEFT JOIN web_sales ON
> wr_order_number = ws_order_number WHERE ws_order_number IS NULL;{code}
> The number of distinct ws_order_number in web_sales table in a typical 10TB
> TPCDS set up is just 10% of total records. So when we convert this query to
> anti join, instead of 7 billion rows, only 600 million rows are moved to join
> node.
> In the current patch, just one conversion is done. The pattern of
> project->filter->left-join is converted to project->anti-join. This will take
> care of sub queries with “not exists” clause. The queries with “not exists”
> are converted first to filter + left-join and then its converted to anti
> join. The queries with “not in” are not handled in the current patch.
> From execution side, both merge join and map join with vectorized execution
> is supported for anti join.
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