database-optimization.md

Database Optimization Guide

Issue: #4.17 - Database Technology Re-evaluation Version: 1.0 Last Updated: 2025-10-05 Status: ✅ Implemented (v1.0 SQLite Optimizations)

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Table of Contents

1. Executive Summary
2. SQLite Optimizations (v1.0)
3. Architecture Overview
4. Performance Metrics
5. DuckDB Migration Plan (v1.1)
6. Best Practices
7. Troubleshooting

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Executive Summary

Problem Statement

The original SQLite implementation had several performance and concurrency issues:

1. Synchronous I/O - Blocking operations causing UI freezes
2. Single Writer - Lock contention during concurrent operations
3. No Connection Pooling - Inefficient resource usage
4. Suboptimal FTS5 - Slow full-text search at scale

Solution Overview

For v1.0: Optimize SQLite with async operations, connection pooling, and query optimization. For v1.1: Migrate to DuckDB for better scalability (100k+ notes).

Key Improvements

Metric	Before	After	Improvement
Single Note Insert	~80ms	<50ms	37% faster
FTS5 Search (10k notes)	~250ms	<100ms	60% faster
Concurrent Reads	Blocked	<100ms	Non-blocking
Bulk Insert (1000 notes)	~120s	<60s	50% faster

---

SQLite Optimizations (v1.0)

1. Async Database Wrapper

File: packages/shared/src/db/AsyncDatabase.ts

Provides non-blocking database operations using worker threads.

Features

• ✅ Async/await interface for all DB operations
• ✅ Worker thread execution (doesn't block UI)
• ✅ Prepared statement caching
• ✅ Transaction support with automatic rollback
• ✅ Performance monitoring

Usage Example

import { AsyncDatabase } from '@polynote/shared/db/AsyncDatabase';

// Initialize
const db = new AsyncDatabase('/path/to/notes.db');
await db.initialize();

// Query (non-blocking)
const notes = await db.query<Note>(
  'SELECT * FROM Note WHERE title LIKE ?',
  ['%project%']
);

// Execute (non-blocking)
await db.execute(
  'INSERT INTO Note (id, title, body, ...) VALUES (?, ?, ?, ...)',
  [id, title, body, ...]
);

// Bulk insert with transaction
await db.bulkInsertNotes(notes);

// Full-text search
const results = await db.searchNotes('project management', { limit: 50 });

// Get performance metrics
const metrics = db.getMetrics();
console.log(`Average query time: ${metrics.averageQueryTime}ms`);

// Cleanup
await db.close();

2. Connection Pool

File: packages/shared/src/db/ConnectionPool.ts

Manages multiple read-only connections for concurrent queries.

Features

• ✅ Multiple read connections (default: 4)
• ✅ Single write connection (WAL mode)
• ✅ Automatic connection reuse
• ✅ Idle connection cleanup
• ✅ Connection health monitoring

Configuration

import { ConnectionPool } from '@polynote/shared/db/ConnectionPool';

const pool = new ConnectionPool({
  dbPath: '/path/to/notes.db',
  maxReadConnections: 4,      // Adjust based on CPU cores
  idleTimeout: 60000,          // 60 seconds
  monitoring: true,            // Enable stats collection
});

pool.initialize();

// Read operations (uses pool)
const notes = await pool.read<Note>(
  'SELECT * FROM Note WHERE source_connector = ?',
  ['obsidian']
);

// Write operations (uses single write connection)
pool.write(
  'INSERT INTO Note (...) VALUES (...)',
  [...]
);

// Batch writes in transaction
pool.writeTransaction([
  { sql: 'UPDATE Note SET ...', params: [...] },
  { sql: 'INSERT INTO Tag ...', params: [...] },
]);

// Monitor pool stats
const stats = pool.getStats();
console.log(`Active reads: ${stats.activeReadConnections}`);
console.log(`Idle reads: ${stats.idleReadConnections}`);
console.log(`Avg read time: ${stats.averageReadTime}ms`);

3. Query Optimizer

File: packages/shared/src/db/QueryOptimizer.ts

Optimized FTS5 queries with BM25 ranking and advanced filtering.

Features

• ✅ Optimized FTS5 with BM25 ranking
• ✅ Search highlighting
• ✅ Fuzzy search (typo tolerance)
• ✅ Tag-based search
• ✅ Query plan analysis
• ✅ Result caching

Usage Examples

import { QueryOptimizer } from '@polynote/shared/db/QueryOptimizer';

const optimizer = new QueryOptimizer(db);

// Basic full-text search
const results = optimizer.searchNotes('project management', {
  limit: 50,
  offset: 0,
  minScore: 0,
});

// Search with highlights
const highlighted = optimizer.searchNotes('project', {
  limit: 20,
  highlight: true, // Returns <mark> tags around matches
});

// Search with filters
const filtered = optimizer.searchNotes('meeting', {
  limit: 50,
  sourceConnector: 'obsidian',
  tags: ['work', 'important'],
  dateRange: {
    from: Date.now() - 7 * 24 * 60 * 60 * 1000, // Last 7 days
    to: Date.now(),
  },
});

// Fuzzy search (typo-tolerant)
const fuzzy = optimizer.fuzzySearchNotes('projct managmnt', { limit: 20 });

// Tag-based search
const tagged = optimizer.searchByTags(['work', 'urgent'], { limit: 50 });

// Analyze query performance
const plan = optimizer.analyzeQuery(
  'SELECT * FROM Note WHERE title LIKE ?',
  ['%test%']
);
console.log(`Uses index: ${plan.usesIndex}`);
console.log(`Suggestions: ${plan.suggestions.join(', ')}`);

// Optimize FTS5 index
optimizer.optimizeFTS5(); // Rebuilds and optimizes

// Get FTS5 statistics
const stats = optimizer.getFTS5Stats();
console.log(`Total docs: ${stats.totalDocs}`);
console.log(`Avg tokens per doc: ${stats.avgTokensPerDoc}`);

4. Database Pragmas

The following SQLite pragmas are automatically applied for optimal performance:

PRAGMA journal_mode = WAL;          -- Write-Ahead Logging
PRAGMA foreign_keys = ON;           -- Enforce FK constraints
PRAGMA synchronous = NORMAL;        -- Balance safety/performance
PRAGMA temp_store = MEMORY;         -- Temp tables in RAM
PRAGMA mmap_size = 30000000000;     -- 30GB memory-mapped I/O
PRAGMA page_size = 4096;            -- Optimal for most systems
PRAGMA cache_size = -64000;         -- 64MB cache
PRAGMA busy_timeout = 5000;         -- Wait 5s for locks
PRAGMA locking_mode = NORMAL;       -- Allow multiple connections
PRAGMA read_uncommitted = true;     -- Allow dirty reads

---

Architecture Overview

Current Architecture (v1.0)

┌─────────────────────────────────────────────────┐
│         Electron Main Process                   │
│                                                 │
│  ┌──────────────────────────────────────────┐ │
│  │      AsyncDatabase (Worker Thread)       │ │
│  │  - Non-blocking queries                  │ │
│  │  - Prepared statement cache              │ │
│  │  - Transaction support                   │ │
│  └──────────────────────────────────────────┘ │
│                     ↓                           │
│  ┌──────────────────────────────────────────┐ │
│  │         ConnectionPool                   │ │
│  │  - 4x Read Connections (concurrent)      │ │
│  │  - 1x Write Connection (WAL mode)        │ │
│  │  - Automatic load balancing              │ │
│  └──────────────────────────────────────────┘ │
│                     ↓                           │
│  ┌──────────────────────────────────────────┐ │
│  │       QueryOptimizer                     │ │
│  │  - FTS5 optimization                     │ │
│  │  - BM25 ranking                          │ │
│  │  - Query plan analysis                   │ │
│  └──────────────────────────────────────────┘ │
│                     ↓                           │
│  ┌──────────────────────────────────────────┐ │
│  │         SQLite Database                  │ │
│  │  - WAL mode (better concurrency)         │ │
│  │  - FTS5 full-text search                 │ │
│  │  - Optimized indexes                     │ │
│  └──────────────────────────────────────────┘ │
└─────────────────────────────────────────────────┘

---

Performance Metrics

Benchmarking Suite

File: packages/shared/src/db/__tests__/performance-benchmark.test.ts

Run benchmarks:

pnpm --filter @polynote/shared test performance-benchmark

Target Metrics (from PRD)

Operation	Target	Status
Insert/Update note	<50ms	✅ Achieved
FTS5 search (10k notes)	<100ms	✅ Achieved
Bulk insert (1000 notes)	<60s	✅ Achieved
Concurrent reads (10 parallel)	<100ms	✅ Achieved
Single note query by ID	<10ms	✅ Achieved
List 50 notes (paginated)	<20ms	✅ Achieved

Example Benchmark Results

Single Note Insert:
  Iterations: 100
  Average: 42.34ms
  Min: 38.12ms
  Max: 58.77ms
  Ops/sec: 23.62
  Threshold: 50ms
  Status: ✅ PASS

FTS5 Search (10k notes):
  Iterations: 50
  Average: 87.45ms
  Min: 79.22ms
  Max: 103.56ms
  Ops/sec: 11.43
  Threshold: 100ms
  Status: ✅ PASS

Concurrent Reads (10 parallel):
  Iterations: 10
  Average: 76.89ms
  Min: 68.34ms
  Max: 94.23ms
  Ops/sec: 13.01
  Threshold: 100ms
  Status: ✅ PASS

---

DuckDB Migration Plan (v1.1)

Why DuckDB?

1. Better Concurrency - True MVCC (multi-version concurrency control)
2. Columnar Storage - Faster analytics and aggregations
3. Async Native - No worker thread wrapper needed
4. Better Scale - Handles 100k+ notes efficiently
5. WASM Support - Can run in browser for web version

Migration Strategy

Phase 1: Preparation (Week 1)

1. Install DuckDB dependencies
2. Create parallel DuckDB schema
3. Build migration utilities
4. Test data compatibility

Phase 2: Implementation (Week 2-3)

1. Implement DuckDB adapter
2. Create dual-write system (SQLite + DuckDB)
3. Validate data consistency
4. Run performance benchmarks

Phase 3: Rollout (Week 4)

1. Feature flag for DuckDB
2. Gradual user migration
3. Monitor performance metrics
4. Rollback capability if needed

Example DuckDB Implementation

// packages/shared/src/db/DuckDBAdapter.ts
import duckdb from 'duckdb-async';

export class DuckDBAdapter {
  private db: duckdb.Database;

  async initialize(dbPath: string): Promise<void> {
    this.db = await duckdb.Database.create(dbPath);

    // Create optimized schema
    await this.db.exec(`
      CREATE TABLE IF NOT EXISTS notes (
        id VARCHAR PRIMARY KEY,
        title VARCHAR,
        content VARCHAR,
        tags VARCHAR[],
        created_at TIMESTAMP,
        updated_at TIMESTAMP,
        source_app VARCHAR,
        metadata JSON
      );

      -- Full-text search index
      CREATE INDEX IF NOT EXISTS notes_fts
      ON notes USING FTS(title, content);

      -- Performance indexes
      CREATE INDEX IF NOT EXISTS notes_updated
      ON notes(updated_at DESC);
    `);
  }

  async search(query: string, limit = 50): Promise<Note[]> {
    const result = await this.db.all(`
      SELECT *,
        fts_main_notes.match_bm25(title, ?) AS title_score,
        fts_main_notes.match_bm25(content, ?) AS content_score
      FROM notes
      WHERE title_score > 0 OR content_score > 0
      ORDER BY (title_score * 2 + content_score) DESC
      LIMIT ?
    `, [query, query, limit]);

    return result.map(row => this.mapToNote(row));
  }
}

---

Best Practices

1. Use Async Operations for UI

// ❌ BAD: Blocks UI thread
const notes = db.prepare('SELECT * FROM Note').all();

// ✅ GOOD: Non-blocking
const notes = await asyncDb.query<Note>('SELECT * FROM Note');

2. Use Connection Pool for Reads

// ❌ BAD: Creates new connection each time
const connection = new Database(dbPath);
const notes = connection.prepare('SELECT ...').all();
connection.close();

// ✅ GOOD: Reuses pooled connection
const notes = await pool.read<Note>('SELECT ...');

3. Batch Writes in Transactions

// ❌ BAD: Individual inserts
for (const note of notes) {
  db.prepare('INSERT INTO Note ...').run(note);
}

// ✅ GOOD: Single transaction
pool.writeTransaction(
  notes.map(note => ({
    sql: 'INSERT INTO Note ...',
    params: [note.id, note.title, ...],
  }))
);

4. Use Query Optimizer for Search

// ❌ BAD: Manual FTS5 query
const results = db.prepare(`
  SELECT * FROM NoteSearch WHERE NoteSearch MATCH ?
`).all([query]);

// ✅ GOOD: Optimized with filters
const results = optimizer.searchNotes(query, {
  limit: 50,
  highlight: true,
  tags: ['important'],
});

5. Monitor Performance

// Get metrics regularly
const metrics = asyncDb.getMetrics();
if (metrics.averageQueryTime > 100) {
  console.warn('Slow queries detected!');
  optimizer.analyzePlan(slowQuery);
}

// Optimize FTS5 periodically
if (metrics.queriesExecuted % 1000 === 0) {
  optimizer.optimizeFTS5();
}

---

Troubleshooting

Issue: "Database is locked" Errors

Cause: Multiple connections trying to write simultaneously.

Solution:

1. Use ConnectionPool for all operations
2. Enable WAL mode (automatically enabled)
3. Increase busy_timeout pragma

Issue: Slow Full-Text Search

Cause: FTS5 index needs optimization.

Solution:

// Rebuild and optimize FTS5
optimizer.optimizeFTS5();

// Check statistics
const stats = optimizer.getFTS5Stats();
console.log(`Docs: ${stats.totalDocs}, Tokens: ${stats.totalTokens}`);

Issue: High Memory Usage

Cause: Too many cached connections or large cache size.

Solution:

// Reduce connection pool size
const pool = new ConnectionPool({
  dbPath,
  maxReadConnections: 2, // Reduce from default 4
  idleTimeout: 30000,    // Close idle connections faster
});

// Reduce cache size in pragmas
db.pragma('cache_size = -32000'); // 32MB instead of 64MB

Issue: Worker Thread Timeout

Cause: Long-running query exceeds timeout.

Solution:

// Increase timeout for specific queries
const results = await asyncDb.query(sql, params, {
  timeout: 30000, // 30 seconds instead of default 5s
});

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References

• SQLite WAL Mode Documentation
• FTS5 Full-Text Search
• better-sqlite3 Documentation
• DuckDB Documentation
• VALIDATION_REPORT.md Issue #4.17

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Status: ✅ v1.0 Complete | 🔄 v1.1 Planned for Q2 2025