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https://issues.apache.org/jira/browse/CALCITE-1959?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16135787#comment-16135787
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Zain Humayun commented on CALCITE-1959:
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[~jcamachorodriguez] can you please review? Thanks!
https://github.com/apache/calcite/pull/524
> Reduce the amount of Metadata and table name calls in Druid
> -----------------------------------------------------------
>
> Key: CALCITE-1959
> URL: https://issues.apache.org/jira/browse/CALCITE-1959
> Project: Calcite
> Issue Type: Improvement
> Components: druid
> Reporter: Zain Humayun
> Assignee: Zain Humayun
>
> Currently in the Druid adapter, when a model definition file is not provided,
> query times can be quite slow due to excessive metadata and table names
> calls. Initial investigation reveals that a simple query like
> {code:sql}
> SELECT * from table
> {code}
> produces at least 30 http calls for fetching the table names, and another 30
> calls for meta data. This slows down the query considerably, even when the
> individual calls themselves are relatively quick.
> The source of the issue seems to be {{DruidSchema#getTableMap}}, as this
> method dispatches calls to both {{DruidConnectionImpl#metadata}} and
> {{DruidConnectionImpl#tableNames}}. In addition, {{DruidTable#create}} makes
> another call to {{DruidConnectionImpl#metadata}} even if it's given the
> populated fields as arguments.
> {{getTableMap}} is called fairly often indirectly from many places, including
> the validator, so as the query becomes larger, the problems gets a lot worse.
> Ideally, one would provide a model definition to prevent this, but doing so
> is not always possible/preferred for users.
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