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07 PostgreSQL 实战与最佳实践 ​

本章通过实际案例展示 PostgreSQL 的高级应用,包括高可用架构、性能调优、安全加固、监控告警等生产环境最佳实践。

7.1 高可用架构 ​

7.1.1 主从复制 ​

流复制(Streaming Replication):

ini
# 主库配置(postgresql.conf)
wal_level = replica
max_wal_senders = 10
max_replication_slots = 10
hot_standby = on

# 主库配置(pg_hba.conf)
host replication repl_user 192.168.1.0/24 md5
sql
-- 主库:创建复制用户
CREATE USER repl_user WITH REPLICATION PASSWORD 'repl_password';

-- 主库:创建复制槽(可选,防止 WAL 过早删除)
SELECT pg_create_physical_replication_slot('replica_1');
bash
# 从库:基础备份
pg_basebackup -h master_host -U repl_user -D /var/lib/postgresql/15/main -Fp -Xs -P

# 从库:配置 standby.signal
touch /var/lib/postgresql/15/main/standby.signal

# 从库:配置 postgresql.conf
primary_conninfo = 'host=master_host port=5432 user=repl_user password=repl_password'
primary_slot_name = 'replica_1'
hot_standby = on

# 从库:启动
systemctl start postgresql

逻辑复制(Logical Replication,PostgreSQL 10+):

sql
-- 主库:配置
wal_level = logical

-- 主库:创建发布
CREATE PUBLICATION my_publication FOR TABLE users, orders;

-- 从库:创建订阅
CREATE SUBSCRIPTION my_subscription
CONNECTION 'host=master_host port=5432 dbname=mydb user=repl_user'
PUBLICATION my_publication;

流复制 vs 逻辑复制:

特性流复制逻辑复制
复制粒度整个集群可选择表
WAL 级别replicalogical
跨版本必须相同版本可以不同版本
跨平台必须相同平台可以不同平台
性能影响较小较大
适用场景高可用、读扩展数据迁移、部分同步

7.1.2 自动故障转移 ​

使用 Patroni:

yaml
# patroni.yml
scope: postgres-cluster
name: node1

restapi:
  listen: 0.0.0.0:8008
  connect_address: 192.168.1.10:8008

postgresql:
  listen: 0.0.0.0:5432
  connect_address: 192.168.1.10:5432
  data_dir: /var/lib/postgresql/15/main

  authentication:
    replication:
      username: repl_user
      password: repl_password
    superuser:
      username: postgres
      password: postgres_password

bootstrap:
  dcs:
    ttl: 30
    loop_wait: 10
    retry_timeout: 10
    maximum_lag_on_failover: 1048576

  initdb:
    - encoding: UTF8
    - data-checksums

etcd:
  hosts: 192.168.1.10:2379,192.168.1.11:2379,192.168.1.12:2379
bash
# 启动 Patroni
patroni patroni.yml

# 查看集群状态
patronictl -c patroni.yml list

Patroni 架构:

text
                    ┌─────────────┐
                    │   etcd      │
                    │  (DCS)      │
                    └──────┬──────┘
                           │
        ┌──────────────────┼──────────────────┐
        │                  │                  │
   ┌────┴────┐       ┌────┴────┐       ┌────┴────┐
   │ Node 1  │       │ Node 2  │       │ Node 3  │
   │ (Master)│       │(Replica)│       │(Replica)│
   │Patroni  │       │Patroni  │       │Patroni  │
   └─────────┘       └─────────┘       └─────────┘

7.1.3 连接池(PgBouncer) ​

ini
# pgbouncer.ini
[databases]
mydb = host=127.0.0.1 port=5432 dbname=mydb

[pgbouncer]
listen_addr = 0.0.0.0
listen_port = 6432
auth_type = md5
auth_file = /etc/pgbouncer/userlist.txt

pool_mode = transaction  # transaction/session/statement
max_client_conn = 1000
default_pool_size = 20
min_pool_size = 5
reserve_pool_size = 5
reserve_pool_timeout = 3

server_reset_query = DISCARD ALL
server_check_query = SELECT 1
server_check_delay = 30

log_connections = 1
log_disconnections = 1
log_pooler_errors = 1
stats_period = 60
bash
# 启动 PgBouncer
pgbouncer -d /etc/pgbouncer/pgbouncer.ini

# 应用连接 PgBouncer(而不是直接连 PostgreSQL)
postgresql://user:password@pgbouncer_host:6432/mydb

连接池模式对比:

模式连接分配事务临时表适用场景
Session整个会话支持支持需要临时表、会话变量
Transaction每个事务支持不支持大多数应用(推荐)
Statement每条语句不支持不支持简单查询

7.2 性能调优 ​

7.2.1 内存配置 ​

ini
# postgresql.conf

# 共享缓冲区(25% 物理内存)
shared_buffers = 4GB

# 有效缓存大小(75% 物理内存)
effective_cache_size = 12GB

# 工作内存(每个排序/哈希操作)
work_mem = 16MB

# 维护工作内存
maintenance_work_mem = 1GB

# WAL 缓冲区
wal_buffers = 64MB

内存配置计算:

text
假设服务器 16GB 内存:

shared_buffers = 16GB × 25% = 4GB
effective_cache_size = 16GB × 75% = 12GB
work_mem = 16GB / (max_connections × 3) = 16MB(假设 200 连接)
maintenance_work_mem = 1GB(VACUUM、CREATE INDEX 使用)

7.2.2 查询优化 ​

sql
-- 1. 使用 EXPLAIN ANALYZE
EXPLAIN (ANALYZE, BUFFERS, FORMAT TEXT)
SELECT * FROM orders WHERE user_id = 123 AND status = 'completed';

-- 2. 查看慢查询
SELECT
    query,
    calls,
    total_time / 1000 AS total_seconds,
    mean_time / 1000 AS avg_seconds,
    rows
FROM pg_stat_statements
ORDER BY total_time DESC
LIMIT 10;

-- 3. 查找未使用索引的表
SELECT
    schemaname,
    relname,
    seq_scan,
    seq_tup_read,
    idx_scan,
    idx_tup_fetch
FROM pg_stat_user_tables
WHERE seq_scan > 1000
  AND idx_scan < 100
ORDER BY seq_scan DESC;

-- 4. 查找膨胀的表
SELECT
    schemaname,
    tablename,
    pg_size_pretty(pg_total_relation_size(schemaname||'.'||tablename)) AS total_size,
    n_dead_tup,
    n_live_tup,
    CASE WHEN n_live_tup > 0
         THEN round(100.0 * n_dead_tup / (n_live_tup + n_dead_tup), 2)
         ELSE 0
    END AS dead_ratio
FROM pg_stat_user_tables
WHERE n_dead_tup > 10000
ORDER BY dead_ratio DESC;

7.2.3 批量操作优化 ​

sql
-- ❌ 慢:逐条插入
INSERT INTO users (name, email) VALUES ('Alice', 'alice@example.com');
INSERT INTO users (name, email) VALUES ('Bob', 'bob@example.com');
-- ... 重复 10000 次

-- ✅ 快:批量插入
INSERT INTO users (name, email) VALUES
    ('Alice', 'alice@example.com'),
    ('Bob', 'bob@example.com'),
    -- ... 一次插入多行
    ('Zara', 'zara@example.com');

-- ✅ 更快:使用 COPY
COPY users (name, email) FROM '/path/to/data.csv' WITH CSV HEADER;

-- 或使用 \copy(psql 命令)
\copy users (name, email) FROM 'data.csv' WITH CSV HEADER

COPY vs INSERT 性能对比:

方法10 万行数据相对性能
逐条 INSERT~100 秒1x
批量 INSERT(1000 行/批)~5 秒20x
COPY~1 秒100x

7.2.4 并发优化 ​

sql
-- 1. 使用 FOR UPDATE SKIP LOCKED 实现任务队列
SELECT id, task_data
FROM tasks
WHERE status = 'pending'
ORDER BY created_at
LIMIT 10
FOR UPDATE SKIP LOCKED;

-- 2. 使用 advisory locks 防止重复执行
SELECT pg_try_advisory_lock(hashtext('daily_report')) AS locked;
-- 如果返回 true,执行任务
-- 完成后释放
SELECT pg_advisory_unlock(hashtext('daily_report'));

-- 3. 使用部分索引减少索引大小
CREATE INDEX idx_active_users ON users(email) WHERE is_active = true;

-- 4. 使用 BRIN 索引优化时间序列
CREATE INDEX idx_logs_created_brin ON logs USING BRIN (created_at);

7.3 安全加固 ​

7.3.1 用户与权限 ​

sql
-- 1. 创建只读用户
CREATE USER readonly_user WITH PASSWORD 'readonly_password';
GRANT CONNECT ON DATABASE mydb TO readonly_user;
GRANT USAGE ON SCHEMA public TO readonly_user;
GRANT SELECT ON ALL TABLES IN SCHEMA public TO readonly_user;
ALTER DEFAULT PRIVILEGES IN SCHEMA public GRANT SELECT ON TABLES TO readonly_user;

-- 2. 创建应用用户(最小权限)
CREATE USER app_user WITH PASSWORD 'app_password';
GRANT CONNECT ON DATABASE mydb TO app_user;
GRANT USAGE ON SCHEMA public TO app_user;
GRANT SELECT, INSERT, UPDATE, DELETE ON ALL TABLES IN SCHEMA public TO app_user;
GRANT USAGE, SELECT ON ALL SEQUENCES IN SCHEMA public TO app_user;

-- 3. 禁止超级用户远程登录
ALTER USER postgres PASSWORD NULL;

-- 4. 查看用户权限
SELECT
    grantee,
    table_name,
    privilege_type
FROM information_schema.role_table_grants
WHERE grantee = 'app_user';

7.3.2 行级安全(Row Level Security) ​

sql
-- 启用 RLS
ALTER TABLE orders ENABLE ROW LEVEL SECURITY;

-- 创建策略:用户只能看到自己的订单
CREATE POLICY user_orders_policy ON orders
    FOR ALL
    USING (user_id = current_setting('app.current_user_id')::INTEGER);

-- 设置当前用户 ID(应用层设置)
SET app.current_user_id = '123';

-- 查询(自动过滤)
SELECT * FROM orders;  -- 只返回 user_id = 123 的订单

7.3.3 SSL/TLS 加密 ​

ini
# postgresql.conf
ssl = on
ssl_cert_file = '/etc/ssl/certs/server.crt'
ssl_key_file = '/etc/ssl/private/server.key'
ssl_ca_file = '/etc/ssl/certs/ca.crt'

# 强制 SSL
hostssl all all 0.0.0.0/0 md5
hostnossl all all 0.0.0.0/0 reject
bash
# 客户端连接(强制 SSL)
psql "host=db.example.com dbname=mydb user=myuser sslmode=verify-full"

7.3.4 审计日志 ​

sql
-- 安装 pgaudit 扩展
CREATE EXTENSION pgaudit;

-- 配置审计(postgresql.conf)
shared_preload_libraries = 'pgaudit'
pgaudit.log = 'read, write, ddl, role'
pgaudit.log_catalog = on
pgaudit.log_parameter = on

-- 查看审计日志
SELECT * FROM pg_stat_activity WHERE query LIKE '%AUDIT%';

7.4 监控与告警 ​

7.4.1 关键指标 ​

sql
-- 1. 连接数
SELECT count(*) FROM pg_stat_activity;
SELECT count(*) FROM pg_stat_activity WHERE state = 'active';

-- 2. 数据库大小
SELECT
    datname,
    pg_size_pretty(pg_database_size(datname)) AS size
FROM pg_database
ORDER BY pg_database_size(datname) DESC;

-- 3. 表大小
SELECT
    schemaname,
    tablename,
    pg_size_pretty(pg_total_relation_size(schemaname||'.'||tablename)) AS total_size,
    pg_size_pretty(pg_relation_size(schemaname||'.'||tablename)) AS table_size,
    pg_size_pretty(pg_indexes_size(schemaname||'.'||tablename)) AS index_size
FROM pg_tables
WHERE schemaname = 'public'
ORDER BY pg_total_relation_size(schemaname||'.'||tablename) DESC
LIMIT 10;

-- 4. 索引使用情况
SELECT
    schemaname,
    tablename,
    indexrelname,
    idx_scan,
    idx_tup_read,
    idx_tup_fetch
FROM pg_stat_user_indexes
ORDER BY idx_scan DESC;

-- 5. 缓存命中率
SELECT
    sum(heap_blks_read) AS heap_read,
    sum(heap_blks_hit) AS heap_hit,
    CASE WHEN sum(heap_blks_hit) + sum(heap_blks_read) = 0
         THEN 0
         ELSE sum(heap_blks_hit) / (sum(heap_blks_hit) + sum(heap_blks_read))
    END AS ratio
FROM pg_statio_user_tables;

-- 6. 事务 ID 年龄(防止回卷)
SELECT
    datname,
    age(datfrozenxid) AS age
FROM pg_database
ORDER BY age DESC;

7.4.2 监控工具 ​

Prometheus + postgres_exporter:

yaml
# docker-compose.yml
version: '3'
services:
  postgres_exporter:
    image: prometheuscommunity/postgres-exporter
    environment:
      DATA_SOURCE_NAME: "postgresql://monitor_user:password@postgres:5432/mydb?sslmode=disable"
    ports:
      - "9187:9187"

  prometheus:
    image: prom/prometheus
    volumes:
      - ./prometheus.yml:/etc/prometheus/prometheus.yml
    ports:
      - "9090:9090"

  grafana:
    image: grafana/grafana
    ports:
      - "3000:3000"
yaml
# prometheus.yml
scrape_configs:
  - job_name: 'postgresql'
    static_configs:
      - targets: ['postgres_exporter:9187']

Grafana Dashboard:

导入 PostgreSQL Dashboard(ID: 9628)

7.4.3 告警规则 ​

yaml
# Prometheus alerting rules
groups:
  - name: postgresql
    rules:
      - alert: PostgreSQLDown
        expr: pg_up == 0
        for: 1m
        labels:
          severity: critical
        annotations:
          summary: "PostgreSQL 实例宕机"

      - alert: PostgreSQLHighConnections
        expr: pg_stat_activity_count > (pg_settings_max_connections * 0.8)
        for: 5m
        labels:
          severity: warning
        annotations:
          summary: "PostgreSQL 连接数过高 ({{ $value }})"

      - alert: PostgreSQLLowCacheHitRatio
        expr: pg_stat_database_blks_hit{datname!="template0",datname!="template1"} / (pg_stat_database_blks_hit{datname!="template0",datname!="template1"} + pg_stat_database_blks_read{datname!="template0",datname!="template1"}) < 0.98
        for: 15m
        labels:
          severity: warning
        annotations:
          summary: "PostgreSQL 缓存命中率过低 ({{ $value | humanizePercentage }})"

      - alert: PostgreSQLHighDeadTuples
        expr: pg_stat_user_tables_n_dead_tup > 10000
        for: 1h
        labels:
          severity: warning
        annotations:
          summary: "PostgreSQL 死元组过多 ({{ $value }})"

      - alert: PostgreSQLTransactionIDWraparound
        expr: age(pg_database_datfrozenxid{datname!="template0",datname!="template1"}) > 1000000000
        for: 1h
        labels:
          severity: critical
        annotations:
          summary: "PostgreSQL 事务 ID 接近回卷 ({{ $value }})"

7.5 备份与恢复 ​

7.5.1 物理备份(pg_basebackup) ​

bash
# 完整备份
pg_basebackup -h localhost -U backup_user -D /backup/postgres/full_$(date +%Y%m%d) -Ft -z -P

# 增量备份(使用 WAL 归档)
# 配置 postgresql.conf
archive_mode = on
archive_command = 'cp %p /backup/postgres/wal_archive/%f'

# 备份 WAL 文件
pg_basebackup -h localhost -U backup_user -D /backup/postgres/incr_$(date +%Y%m%d) -Ft -z -P -Xs

7.5.2 逻辑备份(pg_dump) ​

bash
# 完整备份
pg_dump -h localhost -U backup_user -Fc -Z 9 mydb > /backup/postgres/mydb_$(date +%Y%m%d).dump

# 并行备份
pg_dump -h localhost -U backup_user -Fd -j 4 -Z 9 mydb -f /backup/postgres/mydb_$(date +%Y%m%d)

# 只备份结构
pg_dump -h localhost -U backup_user -s mydb > /backup/postgres/mydb_schema.sql

# 只备份数据
pg_dump -h localhost -U backup_user -a mydb > /backup/postgres/mydb_data.sql

7.5.3 备份脚本 ​

bash
#!/bin/bash
# backup_postgres.sh

BACKUP_DIR="/backup/postgres"
DATE=$(date +%Y%m%d_%H%M%S)
RETENTION_DAYS=7

# 创建备份目录
mkdir -p $BACKUP_DIR

# 逻辑备份
pg_dump -h localhost -U backup_user -Fc -Z 9 mydb > $BACKUP_DIR/mydb_$DATE.dump

# 物理备份(每周一次)
if [ $(date +%u) -eq 7 ]; then
    pg_basebackup -h localhost -U backup_user -D $BACKUP_DIR/full_$DATE -Ft -z -P
fi

# 清理旧备份
find $BACKUP_DIR -name "*.dump" -mtime +$RETENTION_DAYS -delete
find $BACKUP_DIR -name "full_*" -type d -mtime +30 -exec rm -rf {} \;

# 验证备份
pg_restore --list $BACKUP_DIR/mydb_$DATE.dump > /dev/null 2>&1
if [ $? -eq 0 ]; then
    echo "Backup successful: $DATE"
else
    echo "Backup failed: $DATE"
    exit 1
fi

7.5.4 恢复测试 ​

bash
# 定期测试恢复(重要!)
# 1. 创建测试数据库
createdb -h localhost -U postgres test_restore

# 2. 恢复备份
pg_restore -h localhost -U postgres -d test_restore /backup/postgres/mydb_latest.dump

# 3. 验证数据
psql -h localhost -U postgres -d test_restore -c "SELECT COUNT(*) FROM users;"

# 4. 删除测试数据库
dropdb -h localhost -U postgres test_restore

7.6 常见场景解决方案 ​

7.6.1 电商订单系统 ​

sql
-- 表设计
CREATE TABLE orders (
    id BIGSERIAL PRIMARY KEY,
    user_id INTEGER NOT NULL REFERENCES users(id),
    order_no VARCHAR(32) UNIQUE NOT NULL,
    status VARCHAR(20) NOT NULL DEFAULT 'pending',
    total_amount NUMERIC(10, 2) NOT NULL,
    created_at TIMESTAMP DEFAULT NOW(),
    updated_at TIMESTAMP DEFAULT NOW()
) PARTITION BY RANGE (created_at);

-- 按月分区
CREATE TABLE orders_2026_01 PARTITION OF orders
    FOR VALUES FROM ('2026-01-01') TO ('2026-02-01');

-- 索引
CREATE INDEX idx_orders_user_id ON orders(user_id);
CREATE INDEX idx_orders_status ON orders(status) WHERE status != 'completed';

-- 乐观锁(防止并发更新)
UPDATE orders
SET status = 'completed', updated_at = NOW()
WHERE id = 123 AND updated_at = '2026-09-06 10:00:00';
-- 如果 updated_at 已变,说明被其他事务修改

7.6.2 实时排行榜 ​

sql
-- 使用有序集合(需要 intarray 扩展)
CREATE EXTENSION intarray;

CREATE TABLE leaderboard (
    user_id INTEGER PRIMARY KEY,
    score INTEGER NOT NULL,
    updated_at TIMESTAMP DEFAULT NOW()
);

-- 更新分数
INSERT INTO leaderboard (user_id, score)
VALUES (123, 1000)
ON CONFLICT (user_id) DO UPDATE
SET score = GREATEST(leaderboard.score, EXCLUDED.score),
    updated_at = NOW();

-- 查询排名(使用窗口函数)
SELECT
    user_id,
    score,
    RANK() OVER (ORDER BY score DESC) AS rank
FROM leaderboard
WHERE score > 0
ORDER BY score DESC
LIMIT 100;

7.6.3 多租户系统 ​

sql
-- 方案 1:共享数据库,行级隔离
CREATE TABLE tenants (
    id SERIAL PRIMARY KEY,
    name TEXT NOT NULL
);

CREATE TABLE products (
    id SERIAL PRIMARY KEY,
    tenant_id INTEGER NOT NULL REFERENCES tenants(id),
    name TEXT NOT NULL,
    price NUMERIC(10, 2)
);

-- 启用 RLS
ALTER TABLE products ENABLE ROW LEVEL SECURITY;

CREATE POLICY tenant_isolation ON products
    USING (tenant_id = current_setting('app.tenant_id')::INTEGER);

-- 应用层设置当前租户
SET app.tenant_id = '123';

-- 方案 2:独立 Schema
CREATE SCHEMA tenant_123;
CREATE TABLE tenant_123.products (...);

-- 方案 3:独立数据库(最强隔离)
CREATE DATABASE tenant_123;

7.7 故障排查清单 ​

7.7.1 连接问题 ​

bash
# 1. 检查 PostgreSQL 是否运行
systemctl status postgresql

# 2. 检查端口
netstat -tlnp | grep 5432

# 3. 检查连接数
psql -c "SELECT count(*) FROM pg_stat_activity;"

# 4. 检查最大连接数
psql -c "SHOW max_connections;"

# 5. 终止空闲连接
psql -c "SELECT pg_terminate_backend(pid) FROM pg_stat_activity WHERE state = 'idle' AND state_change < NOW() - INTERVAL '1 hour';"

7.7.2 性能问题 ​

sql
-- 1. 查看当前查询
SELECT pid, now() - query_start AS duration, query
FROM pg_stat_activity
WHERE state = 'active'
ORDER BY duration DESC;

-- 2. 查看锁等待
SELECT
    blocked_locks.pid AS blocked_pid,
    blocking_locks.pid AS blocking_pid,
    blocked_activity.query AS blocked_query,
    blocking_activity.query AS blocking_query
FROM pg_catalog.pg_locks blocked_locks
JOIN pg_catalog.pg_stat_activity blocked_activity ON blocked_activity.pid = blocked_locks.pid
JOIN pg_catalog.pg_locks blocking_locks ON blocking_locks.locktype = blocked_locks.locktype
JOIN pg_catalog.pg_stat_activity blocking_activity ON blocking_activity.pid = blocking_locks.pid
WHERE NOT blocked_locks.granted;

-- 3. 终止长时间运行的查询
SELECT pg_terminate_backend(pid)
FROM pg_stat_activity
WHERE state = 'active'
  AND now() - query_start > interval '5 minutes'
  AND query NOT ILIKE '%pg_terminate_backend%';

-- 4. 查看表膨胀
SELECT
    schemaname,
    tablename,
    pg_size_pretty(pg_total_relation_size(schemaname||'.'||tablename)) AS size,
    n_dead_tup
FROM pg_stat_user_tables
WHERE n_dead_tup > 10000
ORDER BY n_dead_tup DESC;

7.7.3 复制延迟 ​

sql
-- 主库:查看复制状态
SELECT
    client_addr,
    state,
    sent_lsn,
    write_lsn,
    flush_lsn,
    replay_lsn,
    pg_wal_lsn_diff(sent_lsn, replay_lsn) AS lag_bytes
FROM pg_stat_replication;

-- 从库:查看复制延迟
SELECT
    now() - pg_last_xact_replay_timestamp() AS replication_delay;

-- 从库:查看 WAL 接收状态
SELECT * FROM pg_stat_wal_receiver;

本章小结 ​

  • 主从复制(流复制/逻辑复制)实现高可用和读扩展
  • Patroni 提供自动故障转移
  • PgBouncer 连接池提升并发性能
  • 合理配置内存参数(shared_buffers、work_mem)
  • 使用 EXPLAIN ANALYZE 分析慢查询
  • COPY 比 INSERT 快 100 倍
  • 行级安全(RLS)实现多租户隔离
  • 定期备份并测试恢复
  • 监控关键指标:连接数、缓存命中率、死元组、事务 ID 年龄
  • 生产环境必须开启 SSL、配置审计日志

练习:把「07 PostgreSQL 实战与最佳实践」变成可验证能力 ​

  1. 从本文任选一个示例,在可丢弃环境重跑;记录运行时/服务版本、输入、关键输出和清理动作。
  2. 保持其他条件不变,只制造一个边界:空值、重复请求、并发、超时、断连、权限不足或资源耗尽。
  3. 用四句话复盘:现象是什么、原理在哪一层、证据是什么、生产中如何止损。

验收清单

  • [ ] 示例能从空环境重复执行,必要依赖和版本已写明。
  • [ ] 同时保留成功路径与至少一个失败路径,不用“应该没问题”冒充证据。
  • [ ] 结论写明适用边界,并能链接回对应学习路线的能力域。
  • [ ] 练习结束后已清理临时数据、凭据、端口或进程。

对照 数据库练习答案与复盘尺。先交自己的证据再翻答案;答案是镜子,不是传送门。

用心记录每一步成长