txn: reject unsupported shared lock transaction paths

[cfzjywxk]

Issue Number: close #1955

Problem Summary:

Shared lock transactions should not enter commit or lock paths that are incompatible with shared locks. TiDB issue: pingcap/tidb#66154

What is changed:

• Reject a shared-lock key if it is selected or pre-set as the transaction primary key.
• Keep async commit and 1PC disabled for transactions that contain shared locks.
• Reject shared-lock requests in aggressive/fair locking mode.
• Reject shared-lock use in pipelined transactions and pipelined flush.
• Add focused regression tests for the unsupported combinations.

Tests:

• go test ./txnkv/transaction -run "TestLockKeys|TestSharedLockCommitterIncompatibilities"
• go test ./txnkv/transaction
• git diff --check

Summary by CodeRabbit

• Bug Fixes

  • Restricted certain lock configurations from using commit optimizations.
  • Prevented specific lock types from being designated as transaction primary keys.
  • Added validation to block lock mode conflicts in pipelined and aggressive locking contexts.

• Tests

  • Extended test coverage for transaction lock configuration constraints.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: a0f8bade-be80-4083-a376-9fc1ef7b5764

📥 Commits

Reviewing files that changed from the base of the PR and between 839228f and 526450a.

📒 Files selected for processing (4)

• txnkv/transaction/2pc.go
• txnkv/transaction/test_probe.go
• txnkv/transaction/txn.go
• txnkv/transaction/txn_test.go

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📝 Walkthrough

Walkthrough

This PR enforces shared lock transaction mode compatibility constraints in client-go. Changes prevent shared locks from being used in pipelined or aggressive locking transactions, disable async commit and 1PC for shared lock transactions, and reject shared-lock keys as the transaction primary key. Test coverage validates all constraints.

Changes

Shared lock transaction mode constraints

Layer / File(s)	Summary
Lock mode validation txnkv/transaction/txn.go	Pipelined flush logic, aggressive locking exit handler, and LockKeys now reject shared lock requests with explicit errors.
Commit protocol restrictions txnkv/transaction/2pc.go	checkAsyncCommit, checkOnePC, and execute now immediately disable async commit and 1PC when shared locks are present.
Primary key constraints txnkv/transaction/2pc.go	Committer initialization tracks primaryKeyIsSharedLock and validation rejects shared-lock keys as the primary key with a specific error message.
Test probe interface txnkv/transaction/test_probe.go	New CommitterProbe.CheckOnePC() method exposes internal 1PC availability for test introspection.
Test coverage txnkv/transaction/txn_test.go	Refactored TestLockKeys with new subtests for pipelined and aggressive locking rejection; new TestSharedLockCommitterIncompatibilities validates primary key, async/1PC, and pipelined flush constraints.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related issues

• #1955: Directly addresses the enhancement request to reject unsupported shared lock transaction paths by implementing all five compatibility constraints (async commit, 1PC, primary key, pipelined transactions, and aggressive locking) in client-go.

Possibly related PRs

• tikv/client-go#1833: Modifies shared lock handling in 2pc.go for primary key and async/1PC constraints; this PR extends those patterns to cover all transaction modes.

Suggested labels

lgtm, approved, size/M

Suggested reviewers

• zyguan

Poem

🐰 A rabbit hops through transaction modes,
Locking shared paths on many roads,
But pipelined and eager won't align—
Async and 1PC? Just decline!
Primary keys shine bright and clear,
When shared locks vanish from here! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: rejecting unsupported shared lock transaction paths through client-side guards.
Linked Issues check	✅ Passed	All coding requirements from issue #1955 are fully addressed: async commit/1PC disabled for shared locks, shared-lock keys rejected as primary keys, shared locks rejected in pipelined transactions and aggressive/fair locking mode.
Out of Scope Changes check	✅ Passed	All changes align with the stated objectives. The modifications to 2pc.go, txn.go, test_probe.go, and txn_test.go directly implement the five required client-side guards without introducing unrelated changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[cfzjywxk]

@wfxr PTAL

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-05-07 15:32:42.544732139 +0000 UTC m=+368235.418082101: ☑️ agreed by you06.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: you06

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• txnkv/OWNERS [you06]

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