Zain Humayun created CALCITE-1959:
-------------------------------------
Summary: 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
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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