jackye1995 commented on code in PR #10280: URL: https://github.com/apache/iceberg/pull/10280#discussion_r1606896688
########## format/materialized-view-spec.md: ########## @@ -0,0 +1,132 @@ +<!-- + - 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 Materialized View Spec + +## Background and Motivation +Iceberg views are a powerful tool to abstract complex queries and share them among different engines. +However, such views are not materialized by default, which means that they are re-computed every time they are queried. +This can be inefficient for complex queries that are computed frequently. +Iceberg Materialized views are a way to store the results of an Iceberg view to reuse the computation in subsequent queries. + +## Goals +The goal of this spec is to define the metadata associated with materialized views in Iceberg. +Such metadata allows creating and querying Iceberg materialized views across different engines. + +## Specification +A materialized view is an Iceberg view with a respective Iceberg table that stores the results of the view query. +An Iceberg view is considered a materialized view if it has the `materialized.view` property set to `true`. +A materialized view must also reference the storage table identifier in its `materialized.view.storage.table` property. + +The specification for the materialized view properties on the view is as follows: +| Property name | Description | +|--------------------------------------------|-------------------------------------------------------------------------| +| `materialized.view` | This property is used to mark whether a view is a materialized view. If set to `true`, the view is treated as a materialized view.| +| `materialized.view.storage.table` | This property specifies the identifier of the storage table associated with the materialized view.| + +In addition to the properties on the view, the storage table associated with the materialized view has the following properties: + +| Property name | Description | +|--------------------------------------|-------------------------------------------------------------------------------| +| `base.snapshot.[UUID]` | These properties store the snapshot IDs of the base tables at the time the materialized view's data was last updated. Each property is prefixed with `base.snapshot.` followed by the UUID of the base table.| Review Comment: +1. I think supporting time travel is required given it is now a standard ANSI syntax that can be referenced in any MV SQL. Blocking it actually requires more effort to check for time travel query and then fail MV creation. And when you travel by time, I think you need to fix the version it travels to by recording its snapshot ID. Time travel looks at the history entries to identify the snapshot to read. The entry might be removed due to setting of `write.metadata.previous-versions-max`. It might also be modified by accident. So at MV read time the reader should check if the specific version is still there and matches the recorded version in MV. -- 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: issues-unsubscr...@iceberg.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: issues-unsubscr...@iceberg.apache.org For additional commands, e-mail: issues-h...@iceberg.apache.org
