Database Management Guidelines - Dự Án Sát Vách

Tech Stack

• •Engine: PostgreSQL 15
• •Extension: PostGIS 3.3
• •Docker Image: postgis/postgis:15-3.3
• •Migration: Alembic
• •ORM: SQLAlchemy 2.0 + GeoAlchemy2

Core Principles

1. Spatial Data Types

• •GEOGRAPHY vs GEOMETRY:
  • •GEOGRAPHY(POINT, 4326): Dùng cho GPS coordinates (lat/lng), tính khoảng cách bằng meters trên Earth sphere.
  • •GEOMETRY: Dùng cho projected coordinates, nhanh hơn nhưng cần projection.
• •Recommendation: Dùng GEOGRAPHY(POINT, 4326) cho dự án Sát Vách.
  sql

  CREATE TABLE items (
      id SERIAL PRIMARY KEY,
      location GEOGRAPHY(POINT, 4326) NOT NULL
  );
  

2. Spatial Indexing (BẮT BUỘC!)

• •GIST Index: LUÔN LUÔN tạo GIST index trên spatial columns.
  sql

  CREATE INDEX idx_items_location ON items USING GIST(location);
  

• •Performance Impact: Tăng tốc spatial queries lên 1000x.
• •Verify Index: Kiểm tra index đã được tạo.
  sql

  SELECT indexname, indexdef 
  FROM pg_indexes 
  WHERE tablename = 'items';
  

3. Common PostGIS Functions

ST_MakePoint - Tạo Point từ coordinates

-- Tạo point từ longitude, latitude
INSERT INTO items (title, location) VALUES
('Test Item', ST_MakePoint(106.6297, 10.8231));

ST_DWithin - Tìm trong bán kính

-- Tìm items trong bán kính 2000m
SELECT * FROM items
WHERE ST_DWithin(
    location,
    ST_MakePoint(106.6297, 10.8231),
    2000  -- meters
);

ST_Distance - Tính khoảng cách

-- Tính khoảng cách và sắp xếp
SELECT 
    id, 
    title,
    ST_Distance(location, ST_MakePoint(106.6297, 10.8231)) as distance_meters
FROM items
ORDER BY distance_meters
LIMIT 10;

ST_AsGeoJSON - Export GeoJSON

-- Convert geometry sang GeoJSON
SELECT 
    id,
    title,
    ST_AsGeoJSON(location)::json as location
FROM items;

4. Migration Workflow (Alembic)

Setup Alembic

# Initialize Alembic
alembic init alembic

# Edit alembic.ini - set database URL
sqlalchemy.url = postgresql+asyncpg://user:pass@localhost/satvach

Create Migration

# Auto-generate migration từ SQLAlchemy models
alembic revision --autogenerate -m "Create items table"

# Review migration file trong alembic/versions/

Review Migration (QUAN TRỌNG!)

• •Spatial Columns: Alembic có thể không detect đúng Geography type.
  python

  # Trong migration file, sửa thành:
  op.add_column('items', 
      sa.Column('location', 
          geoalchemy2.types.Geography(
              geometry_type='POINT', 
              srid=4326
          ), 
          nullable=False
      )
  )
  

• •GIST Index: Alembic thường bỏ qua GIST index, phải thêm thủ công.
  python

  # Thêm vào migration file:
  op.create_index(
      'idx_items_location',
      'items',
      ['location'],
      postgresql_using='gist'
  )
  

Apply Migration

# Run migrations
alembic upgrade head

# Rollback 1 version
alembic downgrade -1

# Check current version
alembic current

5. Docker Setup

docker-compose.yml

postgres:
  image: postgis/postgis:15-3.3
  environment:
    POSTGRES_DB: satvach
    POSTGRES_USER: admin
    POSTGRES_PASSWORD: admin
  volumes:
    - postgres-data:/var/lib/postgresql/data
    - ./database/init.sql:/docker-entrypoint-initdb.d/init.sql
  ports:
    - "5432:5432"

init.sql

-- Enable PostGIS extension
CREATE EXTENSION IF NOT EXISTS postgis;

-- Create items table
CREATE TABLE IF NOT EXISTS items (
    id SERIAL PRIMARY KEY,
    title VARCHAR(255) NOT NULL,
    description TEXT,
    price DECIMAL(12, 2),
    location GEOGRAPHY(POINT, 4326) NOT NULL,
    image_url TEXT,
    created_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP,
    updated_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP
);

-- Create spatial index
CREATE INDEX IF NOT EXISTS idx_items_location ON items USING GIST(location);

-- Create timestamp index
CREATE INDEX IF NOT EXISTS idx_items_created_at ON items(created_at DESC);

6. Performance Optimization

Analyze Tables

-- Update statistics sau khi insert nhiều data
ANALYZE items;

Vacuum

-- Clean up dead rows
VACUUM ANALYZE items;

Query Optimization

-- Explain query plan
EXPLAIN ANALYZE
SELECT * FROM items
WHERE ST_DWithin(location, ST_MakePoint(106.6297, 10.8231), 2000);

-- Kiểm tra có dùng index không (phải thấy "Index Scan using idx_items_location")

Connection Pooling

• •SQLAlchemy tự động quản lý connection pool.
• •Default: 5 connections, max overflow: 10.
• •Adjust nếu cần:
  python

  engine = create_async_engine(
      DATABASE_URL,
      pool_size=20,
      max_overflow=10
  )
  

7. Backup & Restore

Backup Database

# Backup toàn bộ database
docker exec satvach-db pg_dump -U admin satvach > backup.sql

# Backup chỉ schema
docker exec satvach-db pg_dump -U admin -s satvach > schema.sql

# Backup chỉ data
docker exec satvach-db pg_dump -U admin -a satvach > data.sql

Restore Database

# Restore từ backup
docker exec -i satvach-db psql -U admin satvach < backup.sql

8. Monitoring

Check Database Size

SELECT pg_size_pretty(pg_database_size('satvach'));

Check Table Size

SELECT 
    schemaname,
    tablename,
    pg_size_pretty(pg_total_relation_size(schemaname||'.'||tablename)) AS size
FROM pg_tables
WHERE schemaname = 'public'
ORDER BY pg_total_relation_size(schemaname||'.'||tablename) DESC;

Check Active Connections

SELECT count(*) FROM pg_stat_activity WHERE datname = 'satvach';

Slow Query Log

-- Enable slow query log (queries > 1 second)
ALTER DATABASE satvach SET log_min_duration_statement = 1000;

9. Common Issues & Solutions

Issue: Spatial queries chậm

• •Solution: Kiểm tra GIST index đã tồn tại chưa.
• •Verify: EXPLAIN ANALYZE phải thấy "Index Scan".

Issue: Alembic không detect Geography column

• •Solution: Thêm thủ công trong migration file.

Issue: Connection pool exhausted

• •Solution: Tăng pool_size hoặc kiểm tra connection leaks.

Issue: PostGIS extension not found

• •Solution: Chạy CREATE EXTENSION postgis; trong database.

10. Best Practices

1. •Luôn dùng GIST index cho spatial columns.
2. •Review migrations trước khi apply.
3. •Backup trước khi migrate production database.
4. •Test spatial queries với EXPLAIN ANALYZE.
5. •Monitor database size và connection count.
6. •Vacuum định kỳ để maintain performance.
7. •Dùng Geography type cho GPS coordinates.
8. •Limit results trong queries (pagination).
9. •Index timestamp columns nếu sort by date.
10. •Keep migrations small và focused.