fix: [6980850041] avoid-vote-at-learner-state

[cadem]

Description

Issue(s)

• Close/close/Fix/fix/Resolve/resolve: Issue Link

Checklist

Please check the items in the checklist if applicable.

• Is the user manual updated?
• Are the test cases passed and automated?
• Is there no significant decrease in test coverage?

[gemini-code-assist]

Code Review

This pull request introduces a new error code, TSDB_CODE_SYN_LEARNER_NO_VOTE, and implements a check in syncNodeOnRequestVote to prevent nodes in the learner state from participating in votes. Feedback indicates that this check is currently positioned before the term update logic, which violates the Raft protocol as learners must still update their current term when encountering a higher term. It is also suggested to return a standard Raft reply with the vote denied rather than an error code to prevent candidate timeouts.

[Copilot]

Pull request overview

This PR prevents Raft vote processing when a sync node is in the learner state, adding a dedicated error code to represent “learner cannot vote”.

Changes:

• Add a new sync error code TSDB_CODE_SYN_LEARNER_NO_VOTE and its error string.
• In syncNodeOnRequestVote(), early-return when the node state is TAOS_SYNC_STATE_LEARNER to avoid voting.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
source/util/src/terror.c	Adds human-readable error string for the new sync error code.
include/util/taoserror.h	Registers a new error code ID for “learner cannot vote”.
source/libs/sync/src/syncRequestVote.c	Rejects RequestVote handling when the node is in learner state.

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