PostgreSQL 模式

PostgreSQL 最佳實務快速參考。詳細指南請使用 database-reviewer agent。

何時啟用

撰寫 SQL 查詢或 migrations
設計資料庫 schema
疑難排解慢查詢
實作 Row Level Security
設定連線池

快速參考

索引速查表

| 查詢模式 | 索引類型 | 範例 | |---------|---------|------| | WHERE col = value | B-tree（預設） | CREATE INDEX idx ON t (col) | | WHERE col > value | B-tree | CREATE INDEX idx ON t (col) | | WHERE a = x AND b > y | 複合 | 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) | | 時間序列範圍 | BRIN | CREATE INDEX idx ON t USING brin (col) |

資料類型快速參考

| 使用情況 | 正確類型 | 避免 | |---------|---------|------| | IDs | bigint | int、隨機 UUID | | 字串 | text | varchar(255) | | 時間戳 | timestamptz | timestamp | | 金額 | numeric(10,2) | float | | 旗標 | boolean | varchar、int |

常見模式

複合索引順序：

-- 等值欄位優先，然後是範圍欄位
CREATE INDEX idx ON orders (status, created_at);
-- 適用於：WHERE status = 'pending' AND created_at > '2024-01-01'

覆蓋索引：

CREATE INDEX idx ON users (email) INCLUDE (name, created_at);
-- 避免 SELECT email, name, created_at 時的表格查詢

部分索引：

CREATE INDEX idx ON users (email) WHERE deleted_at IS NULL;
-- 更小的索引，只包含活躍使用者

RLS 政策（優化）：

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

UPSERT：

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

游標分頁：

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

佇列處理：

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 *;

反模式偵測

-- 找出未建索引的外鍵
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)
  );

-- 找出慢查詢
SELECT query, mean_exec_time, calls
FROM pg_stat_statements
WHERE mean_exec_time > 100
ORDER BY mean_exec_time DESC;

-- 檢查表格膨脹
SELECT relname, n_dead_tup, last_vacuum
FROM pg_stat_user_tables
WHERE n_dead_tup > 1000
ORDER BY n_dead_tup DESC;

設定範本

-- 連線限制（依 RAM 調整）
ALTER SYSTEM SET max_connections = 100;
ALTER SYSTEM SET work_mem = '8MB';

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

-- 監控
CREATE EXTENSION IF NOT EXISTS pg_stat_statements;

-- 安全預設值
REVOKE ALL ON SCHEMA public FROM public;

SELECT pg_reload_conf();

postgres-patterns