postgres-patterns

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PostgreSQL Patterns

PostgreSQL 数据库模式

Quick reference for PostgreSQL best practices. For detailed guidance, use the

database-reviewer

agent.

PostgreSQL最佳实践速查指南。如需详细指导，请使用

database-reviewer

Agent。

When to Activate

适用场景

Writing SQL queries or migrations
Designing database schemas
Troubleshooting slow queries
Implementing Row Level Security
Setting up connection pooling

编写SQL查询或迁移脚本
设计数据库模式
排查慢查询问题
实现行级安全（Row Level Security）
配置连接池

Quick Reference

速查参考

Index Cheat Sheet

索引速查表

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)`

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	`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)`

Data Type Quick Reference

数据类型速查表

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`

使用场景	推荐类型	避免使用
标识符	`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	`boolean`	`varchar` 、 `int`

Common Patterns

常见模式

Composite Index Order:

sql

-- 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'

Covering Index:

sql

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

Partial Index:

sql

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

RLS Policy (Optimized):

sql

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

UPSERT:

sql

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

Cursor Pagination:

sql

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

Queue Processing:

sql

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 *;

复合索引顺序：

sql

-- 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：

sql

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

部分索引：

sql

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

优化后的RLS策略：

sql

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

UPSERT操作：

sql

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：

sql

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

队列处理：

sql

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 *;

Anti-Pattern Detection

反模式检测

sql

-- 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;

sql

-- 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;

Configuration Template

配置模板

sql

-- 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();

sql

-- 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();