jackye1995 commented on code in PR #6723: URL: https://github.com/apache/iceberg/pull/6723#discussion_r1148126122
########## docs/branching-and-tagging.md: ########## @@ -0,0 +1,82 @@ +--- +title: "Branching and Tagging" +url: branching +aliases: + - "tables/branching" +menu: + main: + parent: Tables + weight: 0 +--- + +<!-- + - 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. + --> + +# Branching and Tagging + +## Overview + +Iceberg table metadata maintains a log of snapshots which represent the changes applied to a table. +Snapshots are fundamental in Iceberg as they are the basis for reader isolation and time travel queries. +For controlling metadata size and storage costs, Iceberg provides snapshot lifecycle management procedures such as [`expire_snapshots`](../../spark/spark-procedures/#expire-snapshots) for removing unused snapshots and no longer neccessary data files based on table snapshot retention properties. + +**For more sophisticated snapshot lifecycle management, Iceberg also supports branches and tags which are named references to snapshots.** Branches are independent lineages of snapshots and point to the head of the lineage. +Branches and tags have independent lifecycles with regards to snapshot retention during `expireSnapshots`. + +Branching and tagging can be used for handling GDPR requirements and retaining important historical snapshots for auditing. +Branches can also be used as part of data engineering workflows, for enabling experimental branches for testing and validating new jobs. +See below for some examples of how branching and tagging can facilitate these use cases. + + + +The above diagram shows an example of using tag to retain historical snapshots. +In this case a end of year tag is created for the final snapshot in the year, and the tagged snapshot has a retention of 5 years for compliance reasons. + + + +The above diagram shows an example of using an audit branch for validating a write workflow. +Writes are performed on a separate `audit-branch` independent from the main table history. +A validation workflow can validate (e.g. data quality) the state of `audit-branch`. +After validation, the main branch can be `fastForward` to the head of `audit-branch` to update the main table state. + +Branches and tags have a maximum reference age property which control when the reference to the snapshot itself should be expired. Branches have retention properties which define the minimum number of snapshots to retain on a branch as well as the maximum age of individual snapshots to retain on the branch. +These properties are used when the expireSnapshots procedure is run. +For details on the algorithm for expireSnapshots, refer to the [spec](../../../spec#snapshot-retention-policy). + +## Usage Review Comment: I think given the current changes, we can just make this a list of links instead of many different subsections. -- 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]
