rdblue commented on a change in pull request #3188: URL: https://github.com/apache/iceberg/pull/3188#discussion_r805438864
########## File path: site/docs/view-spec.md ########## @@ -0,0 +1,256 @@ +<!-- + - 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. + --> + +# Iceberg View Spec + +## Background and Motivation + +Most compute engines (e.g. Trino and Apache Spark) support logical views, commonly known as ‘views’. A view is a logical table that can be referenced by future queries. Views do not contain any data. Instead, the query stored by the view is executed every time the view is referenced by another query. Views and tables occupy the same namespace. +Each compute engine stores the metadata of the view in its proprietary format in the metastore of choice. Thus, views created from one engine can not be read or altered easily from another engine even when engines share the metastore as well as the storage system. This document standardizes the view metadata for ease of sharing the views across engines. + +## Goals + +* A common metadata format for view metadata, similar to how Iceberg supports a common table format for tables. +* The view metadata format specification + * Includes storage format as well as APIs to write/read the metadata. + * Supports versioning of views to track how a view evolved over time. + +## Overview + +The view metadata storage and retrieval mirrors how Iceberg table metadata is stored and retrieved. The view metadata is stored in a JSON file on object storage for ease of tracking the evolution of the view. Metastore continues to hold the view object with some properties such as database name, owner, create time, last access time and an indication that the object is a view. + +Each ‘CREATE OR REPLACE VIEW’ statement creates a new view version metadata file for that view. Review comment: Did you intend to use backticks and fixed-width font for `CREATE OR REPLACE VIEW`? Is it necessary to state this in terms of SQL? Above, I suggested "all changes to view state create a new metadata file and completely replace the old metadata ..." That seems sufficient to me. ########## File path: site/docs/view-spec.md ########## @@ -0,0 +1,256 @@ +<!-- + - 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. + --> + +# Iceberg View Spec + +## Background and Motivation + +Most compute engines (e.g. Trino and Apache Spark) support logical views, commonly known as ‘views’. A view is a logical table that can be referenced by future queries. Views do not contain any data. Instead, the query stored by the view is executed every time the view is referenced by another query. Views and tables occupy the same namespace. +Each compute engine stores the metadata of the view in its proprietary format in the metastore of choice. Thus, views created from one engine can not be read or altered easily from another engine even when engines share the metastore as well as the storage system. This document standardizes the view metadata for ease of sharing the views across engines. + +## Goals + +* A common metadata format for view metadata, similar to how Iceberg supports a common table format for tables. +* The view metadata format specification + * Includes storage format as well as APIs to write/read the metadata. + * Supports versioning of views to track how a view evolved over time. + +## Overview + +The view metadata storage and retrieval mirrors how Iceberg table metadata is stored and retrieved. The view metadata is stored in a JSON file on object storage for ease of tracking the evolution of the view. Metastore continues to hold the view object with some properties such as database name, owner, create time, last access time and an indication that the object is a view. Review comment: I think it is good to call out that the metadata model matches tables, but this goes a bit too far and states requirements for the metastore, like tracking "database name, owner, create time, last access time, ..." I think this should be more similar to the table spec and bring in a lot of similar wording: > View metadata storage mirrors how Iceberg table metadata is stored and retrieved. View metadata is maintained in metadata files. All changes to view state create a new view metadata file and completely replace the old metadata using an atomic swap. Like Iceberg tables, this atomic swap is delegated to the metastore that tracks tables and/or views by name. The view metadata file tracks the view schema, custom properties, current and past versions, as well as other metadata. -- 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. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
