bowenli86 commented on a change in pull request #8976: [FLINK-12277][table/hive/doc] Add documentation for catalogs URL: https://github.com/apache/flink/pull/8976#discussion_r301241339
########## File path: docs/dev/table/catalog.md ########## @@ -0,0 +1,345 @@ +--- +title: "Catalog" +is_beta: true +nav-parent_id: tableapi +nav-pos: 100 +--- +<!-- +Licensed to the Apache Software Foundation (ASF) under one +or more contributor license agreements. See the NOTICE file +distributed with this work for additional information +regarding copyright ownership. The ASF licenses this file +to you under the Apache License, Version 2.0 (the +"License"); you may not use this file except in compliance +with the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + +Unless required by applicable law or agreed to in writing, +software distributed under the License is distributed on an +"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +KIND, either express or implied. See the License for the +specific language governing permissions and limitations +under the License. +--> + +A catalog can provide information about metadata, such as names, schemas, statistics of tables, and information about how to access data stored in a database or table. Once a catalog is registered to a `TableEnvironment`, all meta-objects defined in a catalog can be accessed from Table API or SQL queries. + + +* This will be replaced by the TOC +{:toc} + + +Catalog Interface +----------------- + +APIs are defined in `Catalog` interface. The interface defines a set of APIs to read and write catalog meta-objects such as database, tables, partitions, views, and functions. + +Users can develop their own catalogs by implementing the interface. + + +Naming Structure in Catalog +--------------------------- + +Flink's catalogs use a strict two-level structure, that is, catalogs contain databases, and databases contain meta-objects. Thus, the full name of a meta-object is always structured as `catalogName`.`databaseName`.`objectName`. + +All registered catalogs are managed by a `CatalogManager` instance in `TableEnvironment`. In order to ease access to meta-objects, `CatalogManager` has a concept of current catalog and current database. Usually how users access meta-objects in a catalog is to specify its full name in the format of `catalogName`.`databaseName`.`objectName`. By setting current catalog and current database, users can use just the meta-object's name in their queries. This greatly simplifies user experience. For example, a previous query as Review comment: I rephrased the sentence in another way ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services
