PostgreSQL 最佳实践模式 (PostgreSQL Patterns)

PostgreSQL 最佳实践快速参考。如需详细指导，请使用 database-reviewer 智能体 (Agent)。

何时激活

编写 SQL 查询或迁移脚本
设计数据库架构 (Schema)
排查慢查询问题
实现行级安全性 (Row Level Security, RLS)
设置连接池 (Connection Pooling)

快速参考

索引速查表 (Index Cheat Sheet)

查询模式	索引类型	示例
`WHERE col = value`	B-tree (默认)	`CREATE INDEX idx ON t (col)`
`WHERE col > value`	B-tree	`CREATE INDEX idx ON t (col)`
`WHERE a = x AND b > y`	复合索引 (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)`
时间序列范围	BRIN	`CREATE INDEX idx ON t USING brin (col)`

数据类型快速参考

用例	正确类型	应避免
ID	`bigint`	`int`, 随机 UUID
字符串	`text`	`varchar(255)`
时间戳	`timestamptz`	`timestamp`
金额	`numeric(10,2)`	`float`
标记位 (Flags)	`boolean`	`varchar`, `int`

常用模式

复合索引顺序：

-- 等值列（Equality columns）在前，范围列（Range columns）在后
CREATE INDEX idx ON orders (status, created_at);
-- 适用于：WHERE status = 'pending' AND created_at > '2024-01-01'

覆盖索引 (Covering Index)：

CREATE INDEX idx ON users (email) INCLUDE (name, created_at);
-- 避免在执行 SELECT email, name, created_at 时进行回表查询 (Table lookup)

部分索引 (Partial Index)：

CREATE INDEX idx ON users (email) WHERE deleted_at IS NULL;
-- 索引更小，仅包含活跃用户

RLS 策略（优化版）：

CREATE POLICY policy ON orders
  USING ((SELECT auth.uid()) = user_id);  -- 包装在 SELECT 中！

UPSERT (更新或插入)：

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 (Cursor Pagination)：

SELECT * FROM products WHERE id > $last_id ORDER BY id LIMIT 20;
-- O(1) 复杂度，优于 O(n) 的 OFFSET

队列处理 (Queue Processing)：

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 (Anti-Pattern Detection)

-- 查找未建立索引的外键
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)
  );

-- 查找慢查询
SELECT query, mean_exec_time, calls
FROM pg_stat_statements
WHERE mean_exec_time > 100
ORDER BY mean_exec_time DESC;

-- 检查表膨胀 (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

-- 连接限制 (根据 RAM 调整)
ALTER SYSTEM SET max_connections = 100;
ALTER SYSTEM SET work_mem = '8MB';

-- 超时设置
ALTER SYSTEM SET idle_in_transaction_session_timeout = '30s';
ALTER SYSTEM SET statement_timeout = '30s';

-- 监控
CREATE EXTENSION IF NOT EXISTS pg_stat_statements;

-- 安全默认值
REVOKE ALL ON SCHEMA public FROM public;

SELECT pg_reload_conf();

postgres-patterns