fix: use a weaker tx consistency level for better perf

[ymc9]

Summary by CodeRabbit

• Refactor
  • Modified database transaction isolation configuration for new transactions.

[claude]

Claude finished @ymc9's task —— View job

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Pull Request Review

Reviewing the transaction consistency level changes for performance improvements.

Review Tasks

• Read and analyze the modified files
• Evaluate the transaction consistency changes
• Assess code quality and best practices
• Check for potential bugs or issues
• Review performance implications
• Examine security concerns
• Evaluate test coverage needs

Analysis

The PR changes the default transaction isolation level from RepeatableRead to ReadCommitted in two locations:

1. base.ts:2086: In the safeTransaction method for manual transactions
2. zenstack-query-executor.ts:93: In automatic mutation transaction wrapping

Code Changes:

// Before
isolationLevel ?? TransactionIsolationLevel.RepeatableRead

// After  
isolationLevel ?? TransactionIsolationLevel.ReadCommitted

Review Feedback

✅ Code Quality & Best Practices

• Changes are minimal and focused
• Consistent application across both transaction creation points
• Maintains the existing pattern of allowing explicit override via isolationLevel parameter

⚠️ Performance Implications

Positive:

• ReadCommitted has lower overhead than RepeatableRead
• Reduces lock contention and blocking between transactions
• Better throughput for concurrent operations

Considerations:

• Trade-off between performance and consistency guarantees
• May allow phantom reads and non-repeatable reads that weren't possible before

⚠️ Potential Issues & Security Concerns

Consistency Changes:

• Non-repeatable reads: Data read twice within the same transaction may differ if another transaction commits changes between reads
• Phantom reads: Range queries may return different results if executed multiple times within the same transaction

Data Integrity:

• Applications relying on repeatable read semantics may now see inconsistent behavior
• Race conditions could emerge in scenarios that previously were protected by stronger isolation

❌ Missing Elements

Documentation:

• No explanation of why this change was made
• No guidance on when users should explicitly use RepeatableRead
• Missing documentation about the behavioral changes

Testing:

• No tests found covering transaction isolation levels
• No verification that existing functionality still works correctly
• No tests demonstrating the performance improvement

🔧 Recommendations

1. Add Documentation:

   // Consider adding JSDoc explaining the default choice
   /**
    * Creates a transaction with ReadCommitted isolation by default for better performance.
    * Use RepeatableRead explicitly if you need stronger consistency guarantees.
    */

2. Consider Making This Configurable:

   • Add a global client option for default isolation level
   • Allow applications to opt into their preferred default

3. Add Tests:

   • Test that isolation level can be explicitly overridden
   • Test concurrent behavior under the new default
   • Regression tests for existing functionality

4. Breaking Change Consideration:

   • This is technically a breaking change in behavior
   • Should be clearly documented in release notes
   • Consider if it warrants a major version bump

📊 Overall Assessment

This change makes sense for performance optimization, but it's a breaking change that could impact application behavior. The implementation is correct, but lacks proper documentation, testing, and consideration of the behavioral impact on existing applications.

Recommendation: Approve with conditions - add tests, documentation, and consider making this configurable rather than a hard default change.

[coderabbitai]

Walkthrough

The pull request changes the default transaction isolation level from RepeatableRead to ReadCommitted in two transaction-handling modules. When initiating new transactions without an existing transaction context, the system now defaults to ReadCommitted unless explicitly overridden.

Changes

Cohort / File(s)	Summary
Transaction isolation level defaults packages/runtime/src/client/crud/operations/base.ts, packages/runtime/src/client/executor/zenstack-query-executor.ts	Modified default transaction isolation level from RepeatableRead to ReadCommitted for new, non-nested transactions. Explicit isolation levels continue to be respected when provided.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

The changes follow a consistent pattern across two files with straightforward logic tweaks to isolation level defaults. No structural complexity, no public API changes, and repetitive modifications reduce review overhead.

Possibly related PRs

• fix(policy): always wrap mutation in a transaction #276: Both PRs modify transaction-start behavior for mutations; this PR changes the default isolation level complementing prior work on transaction wrapping.
• feat: implement sequential transaction #81: Introduced the transaction APIs and TransactionIsolationLevel enum that this PR leverages when applying the new ReadCommitted default.

Poem

🐰 From Repeatable's grasp so tight,
To ReadCommitted's lighter flight,
Default transactions now dance free,
Swifter, simpler, transactions be! 🐇✨

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title Check	✅ Passed	The pull request title "fix: use a weaker tx consistency level for better perf" directly and clearly summarizes the main change in the changeset. Both modified files transition the default transaction isolation level from RepeatableRead to ReadCommitted, which is precisely what "weaker tx consistency level" describes. The title is concise, specific, and avoids vague terminology. A developer scanning the commit history would immediately understand that this change adjusts transaction isolation levels to improve performance.
Docstring Coverage	✅ Passed	No functions found in the changes. Docstring coverage check skipped.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/lower-tx-consistency

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📜 Recent review details

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 981f643 and d80cd16.

📒 Files selected for processing (2)

• packages/runtime/src/client/crud/operations/base.ts (1 hunks)
• packages/runtime/src/client/executor/zenstack-query-executor.ts (1 hunks)

🧰 Additional context used

📓 Path-based instructions (1)

{packages,samples,tests}/**

📄 CodeRabbit inference engine (CLAUDE.md)

Place packages only under packages/, samples/, or tests/

Files:

• packages/runtime/src/client/crud/operations/base.ts
• packages/runtime/src/client/executor/zenstack-query-executor.ts

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (2)

• GitHub Check: build-test (20.x, postgresql)
• GitHub Check: build-test (20.x, sqlite)

🔇 Additional comments (1)

packages/runtime/src/client/executor/zenstack-query-executor.ts (1)

91-95: Weaker isolation appears safe for incremental operations but broader mutation patterns warrant developer review.

Incremental operations (increment/decrement) use atomic SQL expression builders (eb(field, '+', value)), which execute as single SQL statements and are safe under ReadCommitted isolation. However, the original concern about multi-read mutations remains valid—if your mutations perform separate read operations followed by conditional writes, ReadCommitted could permit non-repeatable reads or phantom reads.

The codebase lacks explicit tests validating isolation behavior for concurrent mutations, and there's no documentation explaining why ReadCommitted was chosen. Verify:

1. Whether mutations perform atomic operations or multi-step reads followed by writes
2. If your application handles potential race conditions from concurrent updates
3. Test concurrent incremental operations if they're critical to your use case

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[Copilot]

Pull Request Overview

This PR changes the default transaction isolation level from RepeatableRead to ReadCommitted across the runtime package to improve performance. The weaker consistency level reduces locking overhead while still providing adequate transaction safety for most use cases.

Key Changes:

• Updated default transaction isolation level in query executor
• Updated default transaction isolation level in CRUD operation handlers

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
packages/runtime/src/client/executor/zenstack-query-executor.ts	Changed default isolation level for mutation transactions from RepeatableRead to ReadCommitted
packages/runtime/src/client/crud/operations/base.ts	Changed default isolation level for operation handler transactions from RepeatableRead to ReadCommitted

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