Analysis: Read/Write Traffic Splitting Architecture for Database Replication

[Copilot]

✅ Analysis Complete - Ready for Review

Deliverables

• Comprehensive architecture analysis (36KB)
• Technical design with component specifications
• Sequence diagrams in Mermaid format (27KB) ✨ Updated
• Configuration templates for all major databases (18KB)
• Documentation index and navigation (9.4KB)
• Executive summary for stakeholders (11KB)

Recent Updates

• ✨ Converted all ASCII diagrams to Mermaid format for better rendering
  • 5 sequence diagrams showing runtime behavior
  • 1 decision flowchart showing router logic
  • 2 architecture diagrams showing component structure
• 🔧 Fixed transaction handling: transactions start lazily on first SQL execution (standard JDBC behavior)
• 🔧 Fixed failover logic: tries other replicas before falling back to primary

Key Documents Created

1. READ_WRITE_SPLITTING_ANALYSIS.md - Main technical analysis (1,124 lines)
2. read-write-splitting-sequence-diagram.md - Visual flow diagrams (Mermaid)
3. read-write-splitting-configuration-templates.md - Config examples (440 lines)
4. READ_WRITE_SPLITTING_README.md - Documentation index (288 lines)
5. READ_WRITE_SPLITTING_SUMMARY.md - Executive summary (488 lines)

Recommendation

Approach: SQL Parsing and Automatic Routing

• ✅ Fully transparent (no application changes)
• ✅ Backward compatible (opt-in feature)
• ✅ Leverages existing OJP architecture
• ✅ 8-10 week implementation timeline

No Code Changes Made

This PR contains analysis and documentation only - no code has been modified.

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[rrobetti]

@copilot convert diagrams to mermaid where possible.

[Copilot]

@copilot convert diagrams to mermaid where possible.

Converted all diagrams to Mermaid format in commit fdd6786:

• 5 sequence diagrams (read routing, write routing, transactions, failover, SELECT FOR UPDATE)
• 1 decision flowchart (router logic)
• 2 architecture diagrams (analysis and summary documents)

The Mermaid diagrams now render properly on GitHub and are easier to maintain.

[rrobetti]

@copilot why fall back directly to primary? should it not fallback to another replica first?

[Copilot]

You're absolutely right. Updated in commit de566e6 to try other replicas first before falling back to primary. The failover logic now:

1. Tries the selected replica
2. If it fails, tries the next replica in rotation
3. Only falls back to primary if all replicas are unavailable

Updated the sequence diagram to show "Scenario 4: Replica Failover with Multiple Replicas" demonstrating this behavior, and updated the ReplicaSelector interface to include selectHealthyReplica() method that attempts all replicas.

[rrobetti]

@copilot are you sure a transaction is started imediatelly after setAutoCommit(false) is called? I had the impression the transaction start was delayed, is it not?

[Copilot]

You're correct - transaction start is delayed (lazy). Fixed in commit de566e6.

setAutoCommit(false) only changes the auto-commit mode. The transaction actually starts when the first SQL statement is executed after setting auto-commit to false. This is standard JDBC behavior across PostgreSQL, MySQL, Oracle, and SQL Server.

Updated the sequence diagram to show the transaction starting on first SQL execution, and added clarification in the analysis document explaining the lazy transaction start behavior.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[rrobetti]

The analysis looks good, wait for the migration to Actions to finish before implementing to avoid conflicts.