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https://issues.apache.org/jira/browse/HIVE-23479?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17108721#comment-17108721
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Stamatis Zampetakis commented on HIVE-23479:
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Credits for this discovery go to [~kgyrtkirk]! :)
> Avoid regenerating JdbcSchema for every table in a query
> --------------------------------------------------------
>
> Key: HIVE-23479
> URL: https://issues.apache.org/jira/browse/HIVE-23479
> Project: Hive
> Issue Type: Improvement
> Components: Query Planning
> Reporter: Stamatis Zampetakis
> Priority: Major
>
> Currently {{CalcitePlanner}} generates a complete {{JdbcSchema}} for every
> {{JdbcTable}} in the query.
> https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/parse/CalcitePlanner.java#L3174
> This wastes some resources since every call to {{JdbcSchema#getTable}} needs
> to communicate with the database to bring back the tables belonging to the
> schema. Moreover, the fact that a schema is created during planning is
> counter-intuitive since in principle the schema shouldn't change.
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