[GitHub] [iceberg] jackye1995 commented on a diff in pull request #6723: Docs: Separate page for Branching and Tagging

["jackye1995 (via GitHub)" <gi...@apache.org>]

jackye1995 commented on code in PR #6723:
URL: https://github.com/apache/iceberg/pull/6723#discussion_r1171700213


##########
docs/branching-and-tagging.md:
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@@ -0,0 +1,116 @@
+---
+title: "Branching and Tagging"
+url: branching
+aliases:
+    - "tables/branching"
+menu:
+    main:
+        parent: Tables
+        weight: 0
+---
+
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+ - WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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+ - 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 supports branches and tags which are named references to snapshots with their own independent lifecycles. This lifecycle is controlled by branch and tag level retention policies.** 
+Branches are independent lineages of snapshots and point to the head of the lineage. 
+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).
+
+## Use Cases
+
+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.
+
+### Historical Tags
+
+Tags can be used for retaining important historical snapshots for auditing purposes.
+
+![Historical Tags](../img/historical-snapshot-tag.png)
+
+The above diagram demonstrates retaininig important historical snapshot with the following retention policy, defined 
+via Spark SQL.
+
+1. Retain the latest 5 days of snapshots for 1 week. This can be achieved by setting a branch retention policy where 5 days worth of snapshots will be kept, and the branch reference itself will be retained for 1 week. 

Review Comment:
   it is a bit awkward to have the first example using a branch setting, where the rest are tags. I would suggest moving this to the end after 1 snapshot per year example, and also don't use the "latest 5 days of snapshots for 1 week" example, it might make people think you have to do it this way instead of tag. We can just use a generic example like creating a temp test branch valid for 7 days.



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