tiflash: Add warnings about LOCATION LABELS on ALTER TABLE ... SET TIFLASH REPLICA (#21692) #21696
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…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]>
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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 TiDB documentation to address a known limitation with the LOCATION LABELS clause when setting TiFlash replicas. It clarifies the correct usage and warns users about the current parsing issue, preventing potential misconfigurations and improving the accuracy of the documentation.
Highlights
- Documentation Update for TiFlash Replicas: The documentation for ALTER TABLE ... SET TIFLASH REPLICA has been updated to remove the LOCATION LABELS clause from examples and provide a clear warning against its use, as it currently does not correctly parse multiple labels.
- Improved Replica Verification Example: The example for verifying TiFlash replica distribution has been updated from pd-ctl output to more practical SQL queries using information_schema.
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Code Review
This pull request updates the documentation to warn users against using LOCATION LABELS when setting TiFlash replicas, as it doesn't work correctly with multiple labels. The changes remove the example of using LOCATION LABELS and add an explicit warning note. My review focuses on improving the clarity of the new explanations and the robustness of the example SQL queries. I've suggested rephrasing a couple of sentences for better readability and proposed a more robust way to query for TiFlash nodes in the provided SQL examples.
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[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
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This is an automated cherry-pick of #21692
First-time contributors' checklist
What is changed, added or deleted? (Required)
According to the discussion with @JmPotato , the current implementation of
LOCATION LABELSis 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 LABELSwith 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%BDthen 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)?
Do your changes match any of the following descriptions?