PostgreSQL 模式 (PostgreSQL Patterns)

PostgreSQL 最佳实践的快速参考。有关详细指导，使用 database-reviewer agent。

何时激活

• 编写 SQL 查询或迁移
• 设计数据库架构
• 排查慢查询
• 实施行级安全 (RLS)
• 设置连接池

快速参考

索引备忘单

Query Pattern	Index Type	Example
WHERE col = value	B-tree (default)	CREATE INDEX idx ON t (col)
WHERE col > value	B-tree	CREATE INDEX idx ON t (col)
WHERE a = x AND b > y	Composite	CREATE INDEX idx ON t (a, b)
WHERE jsonb @> '{}'	GIN	CREATE INDEX idx ON t USING gin (col)
WHERE tsv @@ query	GIN	CREATE INDEX idx ON t USING gin (col)
Time-series ranges	BRIN	CREATE INDEX idx ON t USING brin (col)

数据类型快速参考

Use Case	Correct Type	Avoid
IDs	bigint	int, random UUID
Strings	text	varchar(255)
Timestamps	timestamptz	timestamp
Money	numeric(10,2)	float
Flags	boolean	varchar, int

常见模式

组合索引顺序:

--Equality columns first, then range columns
CREATE INDEX idx ON orders (status, created_at);
-- Works for: WHERE status = 'pending' AND created_at > '2024-01-01'

覆盖索引:

CREATE INDEX idx ON users (email) INCLUDE (name, created_at);
-- Avoids table lookup for SELECT email, name, created_at

部分索引:

CREATE INDEX idx ON users (email) WHERE deleted_at IS NULL;
-- Smaller index, only includes active users

RLS 策略 (优化的):

CREATE POLICY policy ON orders
  USING ((SELECT auth.uid()) = user_id);  -- Wrap in SELECT!

UPSERT:

INSERT INTO settings (user_id, key, value)
VALUES (123, 'theme', 'dark')
ON CONFLICT (user_id, key)
DO UPDATE SET value = EXCLUDED.value;

游标分页:

SELECT * FROM products WHERE id > $last_id ORDER BY id LIMIT 20;
-- O(1) vs OFFSET which is O(n)

队列处理:

UPDATE jobs SET status = 'processing'
WHERE id = (
  SELECT id FROM jobs WHERE status = 'pending'
  ORDER BY created_at LIMIT 1
  FOR UPDATE SKIP LOCKED
) RETURNING *;

反模式检测

-- Find unindexed foreign keys
SELECT conrelid::regclass, a.attname
FROM pg_constraint c
JOIN pg_attribute a ON a.attrelid = c.conrelid AND a.attnum = ANY(c.conkey)
WHERE c.contype = 'f'
  AND NOT EXISTS (
    SELECT 1 FROM pg_index i
    WHERE i.indrelid = c.conrelid AND a.attnum = ANY(i.indkey)
  );

-- Find slow queries
SELECT query, mean_exec_time, calls
FROM pg_stat_statements
WHERE mean_exec_time > 100
ORDER BY mean_exec_time DESC;

-- Check table bloat
SELECT relname, n_dead_tup, last_vacuum
FROM pg_stat_user_tables
WHERE n_dead_tup > 1000
ORDER BY n_dead_tup DESC;

配置模板

-- Connection limits (adjust for RAM)
ALTER SYSTEM SET max_connections = 100;
ALTER SYSTEM SET work_mem = '8MB';

-- Timeouts
ALTER SYSTEM SET idle_in_transaction_session_timeout = '30s';
ALTER SYSTEM SET statement_timeout = '30s';

-- Monitoring
CREATE EXTENSION IF NOT EXISTS pg_stat_statements;

-- Security defaults
REVOKE ALL ON SCHEMA public FROM public;

SELECT pg_reload_conf();

相关

• Agent: database-reviewer - 完整的数据库审查工作流
• Skill: clickhouse-io - ClickHouse 分析模式
• Skill: backend-patterns - API 和后端模式