tiflash: Add warnings about LOCATION LABELS on ALTER TABLE ... SET TIFLASH REPLICA (#21692) #21695

ti-chi-bot · 2025-09-01T01:40:25Z

This is an automated cherry-pick of #21692

First-time contributors' checklist

I've signed the Contributor License Agreement, which is required for the repository owners to accept my contribution.

What is changed, added or deleted? (Required)

According to the discussion with @JmPotato , the current implementation of LOCATION LABELS is not correct and may acts does not meet the user want. Fixing the behavior requires manpower, and there is currently no plan or demand from users. So just add warnings about it.

For example, if the user set LOCATION LABELS with the similar string as placement-rule-in-SQL does: https://docs.pingcap.com/zh/tidb/stable/placement-rules-in-sql/#%E6%8C%87%E5%AE%9A%E7%94%9F%E5%AD%98%E5%81%8F%E5%A5%BD

alter table t set tiflash replica 2 LOCATION LABELS "[region, zone, host]"

then the generated placement-rule in PD is

  {
    "group_id": "tiflash",
    ...
    "start_key": "748000000000055fff795f720000000000fa",
    "end_key": "748000000000055fff7a00000000000000f8",
    "role": "learner",
    "count": 2,
    "label_constraints": [
      {
        "key": "engine",
        "op": "in",
        "values": ["tiflash"]
      }
    ],
    "location_labels": [
      "[region, zone, host]"
    ],
  }

but not

  {
    "group_id": "tiflash",
    ...
    "start_key": "748000000000055fff795f720000000000fa",
    "end_key": "748000000000055fff7a00000000000000f8",
    "role": "learner",
    "count": 2,
    "label_constraints": [
      {
        "key": "engine",
        "op": "in",
        "values": ["tiflash"]
      }
    ],
    "location_labels": [
      "region",
      "zone",
      "host"
    ],
  }

Which TiDB version(s) do your changes apply to? (Required)

Tips for choosing the affected version(s):

By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.

For details, see tips for choosing the affected versions (in Chinese).

What is the related PR or file link(s)?

This PR is translated from: tiflash: Add warnings about LOCATION LABELS on ALTER TABLE ... SET TIFLASH REPLICA docs-cn#20829
Other reference link(s):

Do your changes match any of the following descriptions?

Delete files
Change aliases
Need modification after applied to another branch
Might cause conflicts after applied to another branch

…LICA Signed-off-by: JaySon-Huang <[email protected]>

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Signed-off-by: JaySon-Huang <[email protected]>

Co-authored-by: xixirangrang <[email protected]>

gemini-code-assist

Summary of Changes

Hello @ti-chi-bot, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request updates the TiFlash replica documentation to address a known limitation with the LOCATION LABELS clause in ALTER TABLE ... SET TIFLASH REPLICA statements. It removes misleading examples and adds a clear warning to prevent users from encountering unexpected behavior. Additionally, it enhances the verification process for replica distribution by providing direct SQL queries.

Highlights

Documentation Update for TiFlash Replicas: Clarified the usage of ALTER TABLE ... SET TIFLASH REPLICA by removing the LOCATION LABELS clause from examples, as it currently does not function as expected for multiple labels.
Warning on LOCATION LABELS: Added a prominent note warning users that LOCATION LABELS in ALTER TABLE ... SET TIFLASH REPLICA cannot correctly parse multiple labels, advising against its use for this purpose.
Improved Replica Verification: Replaced the pd-ctl command with new SQL queries in the documentation, providing a more user-friendly way to verify the distribution of TiFlash replicas for both partitioned and non-partitioned tables.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point in your pull request via creating an issue comment (i.e. comment on the pull request page) using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands.

Feature	Command	Description
Code Review	`/gemini review`	Performs a code review for the current pull request in its current state.
Pull Request Summary	`/gemini summary`	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in issue comments and review comments.
Help	`/gemini help`	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

gemini-code-assist

Code Review

This pull request updates the documentation to warn users against using LOCATION LABELS when setting TiFlash replicas, as its implementation is incorrect. The changes remove the usage of LOCATION LABELS from examples and add an explicit warning note. The verification method is also updated from pd-ctl to a more convenient SQL query. My review provides suggestions to make the example SQL queries more robust and generic for users.

tiflash/create-tiflash-replicas.md

hfxsd · 2025-09-01T01:52:11Z

/approve

ti-chi-bot · 2025-09-01T01:52:19Z

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hfxsd

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

~~OWNERS~~ [hfxsd]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

JaySon-Huang and others added 6 commits September 1, 2025 01:40

Add warnings about LOCATION LABELS on ALTER TABLE ... SET TIFLASH REP…

43f23b5

…LICA Signed-off-by: JaySon-Huang <[email protected]>

Apply suggestions from code review

827aa8c

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Update format

af58dcd

Signed-off-by: JaySon-Huang <[email protected]>

Apply suggestions from code review

f0a974a

Apply suggestions from code review

1486e65

Co-authored-by: xixirangrang <[email protected]>

Update tiflash/create-tiflash-replicas.md

c7431e4

ti-chi-bot added lgtm needs-1-more-lgtm Indicates a PR needs 1 more LGTM. size/M Denotes a PR that changes 30-99 lines, ignoring generated files. type/cherry-pick-for-release-7.5 This PR is cherry-picked to release-7.5 from a source PR. labels Sep 1, 2025

ti-chi-bot mentioned this pull request Sep 1, 2025

tiflash: Add warnings about LOCATION LABELS on ALTER TABLE ... SET TIFLASH REPLICA #21692

Merged

14 tasks

ti-chi-bot assigned JaySon-Huang Sep 1, 2025

gemini-code-assist bot reviewed Sep 1, 2025

View reviewed changes

tiflash/create-tiflash-replicas.md Show resolved Hide resolved

tiflash/create-tiflash-replicas.md Show resolved Hide resolved

tiflash/create-tiflash-replicas.md Show resolved Hide resolved

ti-chi-bot bot added the approved label Sep 1, 2025

ti-chi-bot bot merged commit 3b4ce7a into pingcap:release-7.5 Sep 1, 2025
9 checks passed

ti-chi-bot bot deleted the cherry-pick-21692-to-release-7.5 branch September 1, 2025 01:54

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

tiflash: Add warnings about LOCATION LABELS on ALTER TABLE ... SET TIFLASH REPLICA (#21692) #21695

tiflash: Add warnings about LOCATION LABELS on ALTER TABLE ... SET TIFLASH REPLICA (#21692) #21695

Uh oh!

ti-chi-bot commented Sep 1, 2025

Uh oh!

gemini-code-assist bot left a comment

Uh oh!

gemini-code-assist bot left a comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

hfxsd commented Sep 1, 2025

Uh oh!

ti-chi-bot bot commented Sep 1, 2025

Uh oh!

Uh oh!

Uh oh!

tiflash: Add warnings about LOCATION LABELS on ALTER TABLE ... SET TIFLASH REPLICA (#21692) #21695

tiflash: Add warnings about LOCATION LABELS on ALTER TABLE ... SET TIFLASH REPLICA (#21692) #21695

Uh oh!

Conversation

ti-chi-bot commented Sep 1, 2025

First-time contributors' checklist

What is changed, added or deleted? (Required)

Which TiDB version(s) do your changes apply to? (Required)

What is the related PR or file link(s)?

Do your changes match any of the following descriptions?

Uh oh!

gemini-code-assist bot left a comment

Choose a reason for hiding this comment

Summary of Changes

Highlights

Footnotes

Uh oh!

gemini-code-assist bot left a comment

Choose a reason for hiding this comment

Code Review

Uh oh!

Uh oh!

Uh oh!

Uh oh!

hfxsd commented Sep 1, 2025

Uh oh!

ti-chi-bot bot commented Sep 1, 2025

Uh oh!

Uh oh!

Uh oh!