Fabian Hueske created FLINK-3738:
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Summary: Refactor TableEnvironment and TranslationContext
Key: FLINK-3738
URL: https://issues.apache.org/jira/browse/FLINK-3738
Project: Flink
Issue Type: Task
Components: Table API
Reporter: Fabian Hueske
Currently the TableAPI uses a static object called {{TranslationContext}} which
holds the Calcite table catalog and a Calcite planner instance. Whenever a
{{DataSet}} or {{DataStream}} is converted into a {{Table}} or registered as a
{{Table}} on the {{TableEnvironment}}, a new entry is added to the catalog. The
first time a {{Table}} is added, a planner instance is created. The planner is
used to optimize the query (defined by one or more Table API operations and/or
one ore more SQL queries) when a {{Table}} is converted into a {{DataSet}} or
{{DataStream}}. Since a planner may only be used to optimize a single program,
the choice of a single static object is problematic.
I propose to refactor the {{TableEnvironment}} to take over the responsibility
of holding the catalog and the planner instance.
- A {{TableEnvironment}} holds a catalog of registered tables and a single
planner instance.
- A {{TableEnvironment}} will only allow to translate a single {{Table}}
(possibly composed of several Table API operations and SQL queries) into a
{{DataSet}} or {{DataStream}}.
- A {{TableEnvironment}} is bound to an {{ExecutionEnvironment}} or a
{{StreamExecutionEnvironment}}. This is necessary to create data source or
source functions to read external tables or streams.
- {{DataSet}} and {{DataStream}} need a reference to a {{TableEnvironment}} to
be converted into a {{Table}}. This will prohibit implicit casts as currently
supported for the DataSet Scala API.
- A {{Table}} needs a reference to the {{TableEnvironment}} it is bound to.
Only tables from the same {{TableEnvironment}} can be processed together.
- The {{TranslationContext}} will be completely removed.
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