apache/iceberg

Docs: Clarify Spark branch write precedence over WAP branch

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#15916 opened on Apr 9, 2026

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Description

Feature Request / Improvement

After https://github.com/apache/iceberg/pull/15288, Spark Writing to Branches doc (docs/docs/spark-writes.md) no longer matches that in codes.

   * <p>The target branch can be specified via table identifier, write option, or in SQL:
   *
   * <ul>
   *   <li>The identifier and option branches can't conflict. If both are set, they must match.
   *   <li>Identifier and option branches take priority over the session WAP branch.
   *   <li>If neither the option nor the identifier branch is set and WAP is enabled for this table,
   *       use the WAP branch from the session SQL config.
   * </ul>
   *
   * <p>Note: WAP ID and WAP branch cannot be set at the same time.
   *
   * <p>Note: The target branch may be created during the write operation if it does not exist.

Query engine

Spark

Willingness to contribute

  • I can contribute this improvement/feature independently
  • I would be willing to contribute this improvement/feature with guidance from the Iceberg community
  • I cannot contribute this improvement/feature at this time

Contributor guide

Tech stack
java
Domain
documentation
Issue type
documentation
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Review linked PR #15288 for contextUnderstand current branch precedence logic
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
80
Research direction
Start by reading the current documentation at docs/docs/spark writes.md and compare it with the code comments, especially those updated in PR #15288. The key point is that identifier and option branches take priority over the WAP branch. Identify where the documentation diverges and rewrite the relevant section to match the code. Ensure the updated doc explains the precedence clearly and concisely.