Update follower read and learner read descriptions #21470
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Signed-off-by: zyguan <[email protected]>
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Summary of Changes
Hello @zyguan, 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 documentation for TiDB's tidb_replica_read system variable, specifically clarifying the behavior of follower and learner read modes. The changes reflect recent adjustments in TiDB's replica reading logic and provide important version-specific details for older releases to ensure the documentation is accurate and up-to-date.
Highlights
followerread mode behavior: The description fortidb_replica_readset tofollowerhas been updated. It now clarifies that TiDB also considers reading from learner replicas with equal priority, and if no follower or learner replicas are available, it will fall back to reading from the leader replica.learnerread mode behavior: The description fortidb_replica_readset tolearnerhas been revised. Previously, it stated that an error would be returned if no learner replica was available; now, it clarifies that TiDB will attempt to read from available leader or follower replicas in such cases.- Version-specific notes: A new note has been added to specify the behavior for TiDB versions up to and including v7.5, detailing that
followerandlearnerread modes would return an error if no appropriate replicas were available, contrasting with the newer fallback behavior.
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Code Review
This pull request updates the documentation for follower and learner reads to reflect new behaviors in recent TiDB versions. The changes clarify that when tidb_replica_read is set to follower or learner, TiDB will now fall back to other replica types if the preferred type is unavailable, instead of returning an error. My review includes suggestions to improve clarity and conciseness, and to align the text with the documentation style guide. The style guide elements referenced in this review include clarity, simplicity, readability, present tense, and second person.
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
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Co-authored-by: Grace Cai <[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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In response to a cherrypick label: new pull request created to branch |
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First-time contributors' checklist
What is changed, added or deleted? (Required)
The description of follower-read and learner-read is inaccurate, and related behaviors have been adjusted in the newer version of tidb, so the corresponding documentation has been revised accordingly.
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.
What is the related PR or file link(s)?
Do your changes match any of the following descriptions?