tiflash: Add warnings about LOCATION LABELS on ALTER TABLE ... SET TIFLASH REPLICA #21692
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…LICA Signed-off-by: JaySon-Huang <[email protected]>
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Summary of Changes
Hello @JaySon-Huang, 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 addresses a known limitation in how LOCATION LABELS are handled with ALTER TABLE ... SET TIFLASH REPLICA by updating the documentation. Instead of a code fix, which is not currently planned, the changes provide clear guidance and warnings to users about the incorrect parsing of multiple labels, steering them towards more reliable methods for configuring TiFlash replicas and verifying their distribution.
Highlights
- Documentation Update: The documentation for
ALTER TABLE ... SET TIFLASH REPLICAhas been updated to reflect current limitations and best practices. - Warning on LOCATION LABELS: A new warning has been added advising users that
LOCATION LABELSinALTER TABLE ... SET TIFLASH REPLICAcannot correctly parse multiple labels, and its use for configuring TiFlash replicas is not recommended. - Simplified Syntax Example: The example SQL syntax for setting TiFlash replicas has been simplified by removing the
LOCATION LABELSclause. - Updated Verification Method: The method for verifying TiFlash replica distribution has been updated from using
pd-ctlto providing SQL queries for both non-partitioned and partitioned tables.
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Code Review
This pull request updates the documentation to warn against using LOCATION LABELS when setting TiFlash replicas, as the current implementation does not handle multiple labels correctly. The changes rightly guide users to rely on PD's topology-aware scheduling instead. My review includes suggestions to improve the clarity, conciseness, and technical accuracy of the documentation. I've recommended rephrasing some sentences to be more direct and to adhere to the style guide's use of the second-person voice. I also identified a potential issue in a new SQL query example and suggested a more robust alternative to ensure its correctness. A minor formatting inconsistency was also pointed out.
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Signed-off-by: JaySon-Huang <[email protected]>
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Co-authored-by: xixirangrang <[email protected]>
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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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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?