Add accurate SQLite3 Server documentation

- Clear distinction between Admin Interface (port 6032) and SQLite3 Server (port 6030)
- Explanation of MySQL-to-SQLite gateway functionality
- Simple usage examples and common operations
- Vector search integration with sqlite-vec
- Correct authentication using mysql_users table
- Removed incorrect assumptions about non-existent configuration options

doc/SQLite3-Server.md

@@ -0,0 +1,155 @@
+# ProxySQL SQLite3 Server
+
+## Overview
+
+ProxySQL provides a built-in SQLite3 server that acts as a MySQL-to-SQLite gateway. When started with the `--sqlite3-server` option, it listens on port 6030 (by default) and translates MySQL protocol queries into SQLite commands, converting the responses back to MySQL format for the client.
+
+This is the magic of the feature: MySQL clients can use standard MySQL commands to interact with a full SQLite database, with ProxySQL handling all the protocol translation behind the scenes.
+
+## Important Distinction
+
+- **Admin Interface**: Always enabled, listens on port 6032, provides access to config/stats/monitor databases
+- **SQLite3 Server**: Optional, requires `--sqlite3-server`, listens on port 6030, provides access to empty `main` schema
+
+## Usage
+
+### Starting ProxySQL
+
+```bash
+# Start with SQLite3 server on default port 6030
+proxysql --sqlite3-server
+```
+
+### Connecting
+
+```bash
+# Connect using standard mysql client with valid MySQL credentials
+mysql -h 127.0.0.1 -P 6030 -u your_mysql_user -p
+```
+
+Authentication uses the `mysql_users` table in ProxySQL's configuration.
+
+## What You Get
+
+The SQLite3 server provides:
+- **Single Schema**: `main` (initially empty)
+- **Full SQLite Capabilities**: All SQLite features are available
+- **MySQL Protocol**: Standard MySQL client compatibility
+- **Translation Layer**: Automatic MySQL-to-SQLite conversion
+
+## Common Operations
+
+### Basic SQL
+
+```sql
+-- Check current database
+SELECT database();
+
+-- Create tables
+CREATE TABLE users (id INT, name TEXT);
+
+-- Insert data
+INSERT INTO users VALUES (1, 'john');
+
+-- Query data
+SELECT * FROM users;
+```
+
+### Vector Search (with sqlite-vec)
+
+```sql
+-- Create vector table
+CREATE VECTOR TABLE vec_data (vector float[128]);
+
+-- Insert vector
+INSERT INTO vec_data(rowid, vector) VALUES (1, json('[0.1, 0.2, 0.3,...,0.128]'));
+
+-- Search similar vectors
+SELECT rowid, distance FROM vec_data
+WHERE vector MATCH json('[0.1, 0.2, 0.3,...,0.128]');
+```
+
+### Available Databases
+
+```sql
+-- Show available databases
+SHOW DATABASES;
+
+-- Results:
++----------+
+| database |
++----------+
+| main     |
++----------+
+```
+
+### Use Cases
+
+1. **Data Analysis**: Store and analyze temporary data
+2. **Vector Search**: Perform similarity searches with sqlite-vec
+3. **Testing**: Test SQLite features with MySQL clients
+4. **Prototyping**: Quick data storage and retrieval
+5. **Custom Applications**: Build applications using SQLite with MySQL tools
+
+## Limitations
+
+- Only one database: `main`
+- No access to ProxySQL's internal databases (config, stats, monitor)
+- Tables and data are temporary (unless you create external databases)
+
+## Security
+
+- Bind to localhost for security
+- Use proper MySQL user authentication
+- Consider firewall restrictions
+- Configure appropriate user permissions in `mysql_users` table
+
+## Examples
+
+### Simple Analytics
+
+```sql
+CREATE TABLE events (
+    timestamp DATETIME DEFAULT CURRENT_TIMESTAMP,
+    event_type TEXT,
+    metrics JSON
+);
+
+INSERT INTO events (event_type, metrics)
+VALUES ('login', json('{"user_id": 123, "success": true}'));
+
+SELECT event_type,
+       json_extract(metrics, '$.user_id') as user_id
+FROM events;
+```
+
+### Time Series Data
+
+```sql
+CREATE TABLE metrics (
+    timestamp DATETIME DEFAULT CURRENT_TIMESTAMP,
+    cpu_usage REAL,
+    memory_usage REAL
+);
+
+-- Insert time series data
+INSERT INTO metrics (cpu_usage, memory_usage) VALUES (45.2, 78.5);
+
+-- Query recent data
+SELECT * FROM metrics
+WHERE timestamp > datetime('now', '-1 hour');
+```
+
+## Connection Testing
+
+```bash
+# Test connection
+mysql -h 127.0.0.1 -P 6030 -u your_mysql_user -p -e "SELECT 1"
+
+# Expected output
++---+
+| 1 |
++---+
+| 1 |
++---+
+```