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https://issues.apache.org/jira/browse/CALCITE-1959?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16138839#comment-16138839
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Zain Humayun edited comment on CALCITE-1959 at 8/23/17 6:27 PM:
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There was an edge case where the create method was given correctly populated
fields, and a non-null connection which meant that it fetched the metadata
twice in total, when it should only do it once. This is why I created another
create method. That's why I changed the order of the code at the end of
{{DruidTableFactory}}.
was (Author: zhumayun):
There was an edge case where the create method was given correctly populated
fields, and a non-null connection which meant that it fetch the metadata twice
in total, when it should only do it once. This is why I created another create
method. That's why I changed the order of the code at the end of
{{DruidTableFactory}}.
> 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
> Fix For: 1.14.0
>
>
> 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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