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From "jingzhang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-5568) Introduce interface for catalog, and provide an in-memory implementation, and integrate with calcite schema
Date Thu, 23 Feb 2017 02:43:44 GMT

    [ https://issues.apache.org/jira/browse/FLINK-5568?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15879755#comment-15879755

jingzhang commented on FLINK-5568:

[~fhueske], thanks for your response. There is still a detail problem need to discuss, that
is, how to convert ExternalCatalogTable to TableSourceTable. I add the question and one solution
in the description. Looking forward to your advices.

> Introduce interface for catalog, and provide an in-memory implementation, and integrate
with calcite schema
> -----------------------------------------------------------------------------------------------------------
>                 Key: FLINK-5568
>                 URL: https://issues.apache.org/jira/browse/FLINK-5568
>             Project: Flink
>          Issue Type: Sub-task
>          Components: Table API & SQL
>            Reporter: Kurt Young
>            Assignee: jingzhang
> The {{TableEnvironment}} now provides a mechanism to register temporary table. It registers
the temp table to calcite catalog, so SQL and TableAPI queries can access to those temp tables.
Now DatasetTable,  DataStreamTable and TableSourceTable can be registered to  {{TableEnvironment}}
as temporary tables.
> This issue wants to provides a mechanism to connect external catalogs such as HCatalog
to the {{TableEnvironment}}, so SQL and TableAPI queries could access to tables in the external
catalogs without register those tables to {{TableEnvironment}} beforehand.
> First, we should point out that there are two kinds of catalog in Flink actually. 
> The first one is external catalog as we mentioned before, it provides CRUD operations
to databases/tables.
> The second one is calcite catalog, it defines namespace that can be accessed in Calcite
queries. It depends on Calcite Schema/Table abstraction. SqlValidator and SqlConverter depends
on the calcite catalog to fetch the tables in SQL or TableAPI.
> So we need to do the following things:
> 1. introduce interface for external catalog, maybe provide an in-memory implementation
first for test and develop environment.
> 2. introduce a mechanism to connect external catalog with Calcite catalog so the tables/databases
in external catalog can be accessed in Calcite catalog. Including convert databases of externalCatalog
to Calcite sub-schemas, convert tables in a database of externalCatalog to  Calcite tables
(only support {{TableSourceTable}}).
> 3. register external catalog to {{TableEnvironment}}.
> There is still a detail problem need to be take into consideration, that is , how to
convert  {{ExternalCatalogTable}} to {{TableSourceTable}}. The question is equals to  convert
 {{ExternalCatalogTable}} to {{TableSource}} because we could  easily get {{TableSourceTable}}
from {{TableSource}}.
> Because different {{TableSource}} often contains different fields to initiate an instance.
E.g. {{CsvTableSource}}  needs path, fieldName, fieldTypes, fieldDelim, rowDelim and so on
to create a new instance , {{KafkaTableSource}} needs configuration and tableName to create
a new instance. So it's not a good idea to let Flink framework be responsible for translate
 {{ExternalCatalogTable}} to different kind of {{TableSourceTable}}. 
> Here is one solution. Let {{TableSource}} specify a converter.
> 1. provide  an Annatition named {{ExternalCatalogCompatible}}. The {{TableSource}} with
the annotation means it is compatible with external catalog, that is, it could be converted
to or from ExternalCatalogTable. This annotation specifies the tabletype and converter of
the tableSource. For example, for {{CsvTableSource}}, it specifies the tableType is csv and
converter class is CsvTableSourceConverter.
> {code}
> @ExternalCatalogCompatible(tableType = "csv", converter = classOf[CsvTableSourceConverter])
> class CsvTableSource(...) {
> ...}
> {code}
> 2. Scan all TableSources with the ExternalCatalogCompatible annotation, save the tableType
and converter in a Map
> 3. When need to convert {{ExternalCatalogTable}} to {{TableSource}} , get the converter
based on tableType. and let converter do convert

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