FlatSQL

SQL queries over raw FlatBuffer storage — A streaming query engine that keeps data in native FlatBuffer format while providing SQL access via SQLite virtual tables.

Live Demo

Try FlatSQL in your browser: https://digitalarsenal.github.io/flatsql/

Installation

npm install flatsql

Quick Start

import { initFlatSQL } from 'flatsql/wasm';

// Initialize
const flatsql = await initFlatSQL();

// Create database with schema
const db = flatsql.createDatabase(`
  table User {
    id: int (id);
    name: string;
    email: string (key);
    age: int;
  }
`, 'myapp');

// Register file identifier for routing
db.registerFileId('USER', 'User');

// Ingest FlatBuffer data (streaming)
db.ingest(flatbufferStream);

// Query with SQL
const result = db.query('SELECT * FROM User WHERE age > 25');
console.log(result.columns, result.rows);

What is FlatSQL?

FlatSQL bridges two technologies:

• FlatBuffers — Google's efficient cross-platform serialization library. Data is stored in binary format with zero-copy access (no parsing/unpacking needed).
• SQLite — The most widely deployed SQL database engine, used here only for SQL parsing and query execution.

The key insight: instead of converting FlatBuffers to SQLite rows (expensive), FlatSQL uses SQLite virtual tables to query FlatBuffer data directly. Your data stays in portable FlatBuffer format, readable by any FlatBuffer tooling, while you get SQL query capabilities.

Why FlatSQL?

Traditional approach:

FlatBuffer → Deserialize → SQLite rows → Query → Serialize → FlatBuffer

FlatSQL approach:

FlatBuffer → Query (via virtual table) → FlatBuffer

Benefits:

• Zero conversion overhead — Data stays in FlatBuffer format
• Streaming ingestion — Indexes built during data arrival, not after
• Portable output — Exported data is standard FlatBuffers, readable by any tooling
• Multi-source federation — Query across multiple FlatBuffer sources with automatic source tagging

Source Code

| Repository | Description | |------------|-------------| | digitalarsenal/flatsql | This project — FlatSQL query engine | | digitalarsenal/flatbuffers | Fork of Google FlatBuffers with WASM support | | flatc-wasm | FlatBuffer compiler running in WebAssembly |

Usage

WASM (Browser/Node.js)

The C++ engine compiles to WebAssembly for cross-platform deployment:

import { initFlatSQL } from 'flatsql/wasm';

const flatsql = await initFlatSQL();

// Create database with schema
const db = flatsql.createDatabase(`
  table User {
    id: int (id);
    name: string;
    email: string (key);
    age: int;
  }
`, 'myapp');

// Register file identifier routing
db.registerFileId('USER', 'User');

// Enable demo field extractors (for testing)
db.enableDemoExtractors();

// Ingest FlatBuffer stream
// Format: [4-byte size LE][FlatBuffer][4-byte size LE][FlatBuffer]...
db.ingest(streamData);

// Query with SQL
const result = db.query('SELECT id, name, email FROM User WHERE age > 25');
console.log(result.columns); // ['id', 'name', 'email']
console.log(result.rows);    // [[1, 'Alice', '[email protected]'], ...]

// Export database
const exported = db.exportData();

// Cleanup
db.destroy();

TypeScript (Pure JavaScript)

A TypeScript implementation for environments where WASM isn't available:

import { FlatSQLDatabase, FlatcAccessor } from 'flatsql';
import { FlatcRunner } from 'flatc-wasm';

const flatc = await FlatcRunner.init();

const schema = `
  namespace App;

  table User {
    id: int (key);
    name: string (required);
    email: string;
    age: int;
  }
`;

const accessor = new FlatcAccessor(flatc, schema);
const db = FlatSQLDatabase.fromSchema(schema, accessor, 'myapp');

// Insert records
db.insert('User', { id: 1, name: 'Alice', email: '[email protected]', age: 30 });
db.insert('User', { id: 2, name: 'Bob', email: '[email protected]', age: 25 });

// Query
const result = db.query('SELECT name, email FROM User WHERE age > 20');
console.log(result.rows);

// Export as standard FlatBuffers
const exported = db.exportData();

Native C++ (Embedded)

For performance-critical applications, link the C++ library directly:

#include <flatsql/database.h>

auto db = flatsql::FlatSQLDatabase::fromSchema(schema, "mydb");

// Register file ID routing
db.registerFileId("USER", "User");

// Set field extractor
db.setFieldExtractor("User", extractUserField);

// Ingest streaming data
size_t recordsIngested = 0;
db.ingest(data, length, &recordsIngested);

// Query
auto result = db.query("SELECT * FROM User WHERE id = 5");
for (size_t i = 0; i < result.rowCount(); i++) {
    std::cout << result.getString(i, "name") << std::endl;
}

Architecture

┌─────────────────────────────────────────────────────────────┐
│                     FlatSQLDatabase                          │
├─────────────────────────────────────────────────────────────┤
│   SchemaParser        │      SQLiteEngine                    │
│   (FlatBuffers IDL)   │      (Virtual Tables)                │
├─────────────────────────────────────────────────────────────┤
│                    TableStore (per table)                    │
│  ┌────────────────────────────────────────────────────────┐ │
│  │  SQLite Indexes            Field Extractors             │ │
│  │  (id, email, timestamp)    (getField callbacks)         │ │
│  └────────────────────────────────────────────────────────┘ │
├─────────────────────────────────────────────────────────────┤
│              StackedFlatBufferStore (append-only)            │
│  ┌──────────────────────────────────────────────────────┐   │
│  │ [Header][FB₁][FB₂][FB₃]...                           │   │
│  └──────────────────────────────────────────────────────┘   │
└─────────────────────────────────────────────────────────────┘

Stream Format

FlatSQL ingests size-prefixed FlatBuffer streams:

[4-byte size LE][FlatBuffer with file_id][4-byte size LE][FlatBuffer]...

The 4-byte file identifier in each FlatBuffer determines which table receives the record.

SQL Support

Supported

• SELECT with column selection
• WHERE with =, <, >, <=, >=, BETWEEN, LIKE, AND, OR
• ORDER BY (ASC/DESC)
• LIMIT and OFFSET
• COUNT(*) aggregate
• Index-accelerated queries on (id) and (key) columns

Not Supported

• JOIN (query one table at a time)
• GROUP BY, HAVING, most aggregates
• INSERT, UPDATE, DELETE (use API methods instead)
• Subqueries, CTEs, window functions

Performance

FlatSQL outperforms traditional SQLite on query operations:

| Operation | FlatSQL | SQLite | Speedup | |-----------|---------|--------|---------| | Point query (by id) | 3.50 ms | 3.93 ms | 1.1x | | Point query (by key) | 5.23 ms | 6.94 ms | 1.3x | | Direct index lookup | 1.56 ms | 3.93 ms | 2.5x | | Full scan | 0.84 ms | 1.25 ms | 1.5x | | Direct iteration | 0.05 ms | 1.25 ms | 25x |

Benchmarks: 10,000 records, 10,000 query iterations, Apple M3 Ultra

Performance Trade-offs

FlatSQL uses SQLite's virtual table (VTable) API to expose FlatBuffer data as queryable tables. This architecture enables SQL queries over raw binary data, but comes with fundamental trade-offs that affect performance characteristics.

Access Paths

FlatSQL provides three access paths with different performance profiles:

| Access Path | Latency | Throughput | Use Case | |-------------|---------|------------|----------| | Zero-Copy API | 1.7 µs | 580K ops/sec | Direct index lookup, returns raw FlatBuffer pointer | | VTable SQL | 12.9 µs | 78K ops/sec | Full SQL queries via SQLite | | Pure SQLite | 2.5 µs | 400K ops/sec | Baseline comparison |

Why VTable Queries Are Slower Than Pure SQLite

SQLite's VTable API has fundamental limitations that prevent FlatSQL from matching pure SQLite query performance:

1. Per-Column Extraction — The xColumn() callback is invoked once per column per row. There is no batch API to extract multiple fields at once, meaning each field access has function call overhead.

2. Mandatory Value Conversion — All values must be converted to SQLite's internal format via sqlite3_result_*() functions. Even though FlatBuffers already store data in an efficient binary format, we must convert strings to SQLite strings, integers to SQLite integers, etc.

3. Row-by-Row Processing — The xNext() callback advances one row at a time with no vectorized or batch iteration. This prevents SIMD optimizations or processing multiple records per call.

4. No Direct Memory Access — SQLite cannot read FlatBuffer memory directly; all data must flow through the VTable callback interface, adding overhead for every field access.

When to Use Each Access Path

Use the Zero-Copy API when:

• You need maximum throughput for point lookups
• You're building hot paths that query by indexed keys
• You can work directly with FlatBuffer data structures

// Zero-copy: returns pointer to raw FlatBuffer (1.7 µs)
const uint8_t* data = db.findRawByIndex("User", "email", email, &len);
auto user = GetUser(data);  // Direct FlatBuffer access

Use VTable SQL when:

• You need complex queries (filtering, sorting, aggregation)
• Query flexibility is more important than raw speed
• You're doing ad-hoc exploration of the data

// VTable SQL: full query capability (12.9 µs)
auto result = db.query("SELECT * FROM User WHERE age > 25 ORDER BY name");

Architecture: SQLite-Backed Indexes

FlatSQL uses SQLite's highly optimized B-tree for indexing (not a custom implementation). This provides:

• Battle-tested performance — SQLite's B-tree is used by billions of devices
• Consistent behavior — Same indexing code path as pure SQLite
• Fast path optimization — Type-specific lookups bypass std::variant overhead

The index stores (key, sequence) → (offset, length) mappings, allowing O(log n) lookups that return pointers directly into the FlatBuffer storage.

Trade-off Summary

| Aspect | FlatSQL | Pure SQLite | |--------|---------|-------------| | Point lookup (indexed) | 1.4x faster (zero-copy API) | Baseline | | SQL queries | 5-7x slower (VTable overhead) | Baseline | | Storage format | FlatBuffers (portable, zero-copy) | SQLite pages | | Data conversion | None (zero-copy) or on-demand | Always required | | Streaming ingest | Append-only, real-time indexing | Row-by-row inserts |

Bottom line: FlatSQL excels when you need streaming ingestion of FlatBuffer data with SQL query capability. Use the zero-copy API for performance-critical lookups; use SQL for complex queries where flexibility matters more than speed.

Building from Source

Prerequisites

• Node.js 18+
• CMake 3.20+ (for WASM builds)
• Emscripten (for WASM builds)

TypeScript Build

npm install
npm run build
npm test

WASM Build

# Clone DA-FlatBuffers (required dependency)
git clone https://github.com/DigitalArsenal/flatbuffers.git ../flatbuffers

# Build WASM
cd cpp
emcmake cmake -B build-wasm -DCMAKE_BUILD_TYPE=Release
cmake --build build-wasm

Output: wasm/flatsql.js and wasm/flatsql.wasm

Run Demo Locally

npm run serve
# Open http://localhost:8081

API Reference

initFlatSQL()

import { initFlatSQL } from 'flatsql/wasm';

const flatsql = await initFlatSQL();

createDatabase(schema, name)

const db = flatsql.createDatabase(schemaString, 'dbname');

db.registerFileId(fileId, tableName)

db.registerFileId('USER', 'User');  // Route "USER" FlatBuffers to User table

db.ingest(data, source?)

const bytesConsumed = db.ingest(uint8ArrayStream);
// Or with source tagging (requires registerSource first):
const bytesConsumed = db.ingest(uint8ArrayStream, 'satellite-1');

db.query(sql)

const result = db.query('SELECT * FROM User WHERE age > 25');
// result.columns: string[]
// result.rows: any[][]

db.exportData()

const data = db.exportData();  // Returns Uint8Array

db.registerSource(sourceName)

db.registerSource('satellite-1');  // Creates User@satellite-1, Post@satellite-1, etc.

db.createUnifiedViews()

db.createUnifiedViews();  // Creates unified views with _source column

db.listSources()

const sources = db.listSources();  // ['satellite-1', 'satellite-2', ...]

Multi-Source Queries

FlatSQL supports federating multiple data sources with the same schema. Each source gets its own set of tables, and you can query them individually or across all sources.

Use Case

Imagine you have multiple satellites streaming telemetry data with the same schema:

// Register sources
db.registerSource('satellite-1');
db.registerSource('satellite-2');
db.registerSource('ground-station');

// Register file IDs and extractors (must be done after registerSource)
db.registerFileId('TELE', 'Telemetry');
db.enableDemoExtractors();

// Create unified views (call once after all sources registered)
db.createUnifiedViews();

// Ingest from different sources
db.ingest(satellite1Stream, 'satellite-1');
db.ingest(satellite2Stream, 'satellite-2');
db.ingest(groundStream, 'ground-station');

// Query a specific source
db.query('SELECT * FROM "Telemetry@satellite-1" WHERE signal > 50');

// Query across all sources (unified view)
db.query('SELECT * FROM Telemetry WHERE timestamp > 1000');

Table Naming Convention

• Source-specific tables: TableName@sourceName (e.g., User@siteA, Telemetry@satellite-1)
• Unified views: TableName (e.g., User, Telemetry) - combines all source tables with a _source column

The _source Column

Unified views include a _source column that identifies which source each row came from:

-- See source for each record
SELECT _source, id, name FROM User LIMIT 10;

-- Count records by source
SELECT _source, COUNT(*) as count FROM User GROUP BY _source;

-- Filter by source in unified view
SELECT * FROM User WHERE _source = 'satellite-1';

License

Apache 2.0

Contributing

Contributions welcome. Please open an issue first to discuss significant changes.

Contact

For questions, licensing inquiries, or commercial support: [email protected]

Built on DA-FlatBuffers and SQLite.