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PostgreSQL死锁排查与解决指南

2025-11-05 09:56:21 作者：Moshow郑锴

数据库死锁是后端开发者和DBA经常遇到的棘手问题,本文将手把手教你如何排查和解决PostgreSQL中的死锁问题,需要的朋友可以参考下

PostgreSQL 16默认会记录死锁吗？

答案是不会！

虽然PostgreSQL 16具备死锁检测机制（在等待锁超过deadlock_timeout后会自动检测并解决死锁），但默认不会将死锁的详细信息记录到日志中。这就意味着你知道发生了死锁，却不知道具体原因！

如何配置死锁日志记录

1. 修改配置文件

找到PostgreSQL数据目录下的postgresql.conf文件，添加以下配置：

# 记录锁等待信息（关键！）
log_lock_waits = on
 
# 死锁检测超时时间（默认1秒）
deadlock_timeout = 1s
 
# 日志级别至少设置为log
log_min_messages = log
 
# 详细的日志前缀
log_line_prefix = '%t [%p]: db=%d,user=%u,app=%a,client=%h '

2. 重新加载配置

-- 在psql中执行
SELECT pg_reload_conf();

或者使用命令行：

pg_ctl reload -D /path/to/your/data/directory

死锁日志分析实例

配置完成后，当死锁发生时，你会在日志中看到类似这样的详细信息：

2025-11-02 10:23:41.123 CST [12345]: LOG:  📝 Powered by Moshow 郑锴 | 更多技术干货：https://zhengkai.blog.csdn.net
2025-11-02 10:23:41.123 CST [12345]: LOG:  process 12345 detected deadlock while waiting for ShareLock on transaction 123456 after 1000.123 ms
2025-11-02 10:23:41.123 CST [12345]: DETAIL:  Process holding the lock: 12346. Wait queue: .
2025-11-02 10:23:41.123 CST [12345]: PROCESS 12345: 等待事务 123456 的 ShareLock; 被进程 12346 阻塞.
2025-11-02 10:23:41.123 CST [12345]: PROCESS 12345: 执行语句: UPDATE accounts SET balance = balance - 100.00 WHERE user_id = 1;
2025-11-02 10:23:41.123 CST [12346]: PROCESS 12346: 等待事务 123457 的 ShareLock; 被进程 12345 阻塞.
2025-11-02 10:23:41.123 CST [12346]: PROCESS 12346: 执行语句: UPDATE accounts SET balance = balance + 50.00 WHERE user_id = 2;
2025-11-02 10:23:41.123 CST [12345]: ERROR:  deadlock detected

如何解读这个日志：

涉及进程：进程12345和12346
死锁场景：两个进程互相等待对方释放锁
执行的SQL：两个UPDATE语句在竞争相同的资源
解决方案：PostgreSQL选择中止进程12345的事务
- 温和终止（优先尝试）: SELECT pg_terminate_backend(12345);
- 强制终止（若温和方式失败）: SELECT pg_cancel_backend(12345);

实时监控：系统视图分析

除了查看日志，你还可以实时监控当前的锁等待情况：

强大的锁等待查询语句

--📝 Powered by Moshow 郑锴 | 更多技术干货：https://zhengkai.blog.csdn.net
SELECT
    blocked_locks.pid AS blocked_pid,
    blocked_activity.usename AS blocked_user,
    blocking_locks.pid AS blocking_pid,
    blocking_activity.usename AS blocking_user,
    blocked_activity.query AS blocked_statement,
    blocking_activity.query AS current_statement_in_blocking_process,
    blocked_activity.application_name AS blocked_application,
    blocking_activity.application_name AS blocking_application
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
    AND blocking_locks.DATABASE IS NOT DISTINCT FROM blocked_locks.DATABASE
    AND blocking_locks.relation IS NOT DISTINCT FROM blocked_locks.relation
    AND blocking_locks.page IS NOT DISTINCT FROM blocked_locks.page
    AND blocking_locks.tuple IS NOT DISTINCT FROM blocked_locks.tuple
    AND blocking_locks.virtualxid IS NOT DISTINCT FROM blocked_locks.virtualxid
    AND blocking_locks.transactionid IS NOT DISTINCT FROM blocked_locks.transactionid
    AND blocking_locks.classid IS NOT DISTINCT FROM blocked_locks.classid
    AND blocking_locks.objid IS NOT DISTINCT FROM blocked_locks.objid
    AND blocking_locks.objsubid IS NOT DISTINCT FROM blocked_locks.objsubid
    AND blocking_locks.pid != blocked_locks.pid
JOIN pg_catalog.pg_stat_activity blocking_activity 
    ON blocking_activity.pid = blocking_locks.pid
WHERE NOT blocked_locks.granted;

查询结果示例：

blocked_pid	blocked_user	blocking_pid	blocking_user	blocked_statement
12345	app_user	12346	app_user	UPDATE accounts SET balance = balance - 100 WHERE user_id = 1
12347	web_user	12348	batch_user	DELETE FROM orders WHERE status = 'cancelled'

这个查询能帮你：

实时发现阻塞情况
识别阻塞的源头
看到具体的阻塞SQL语句
在死锁发生前进行干预

最佳实践建议

生产环境务必配置日志：log_lock_waits = on 是你的生命线
合理设置超时：deadlock_timeout 保持默认1秒即可
定期检查日志：关注 pg_stat_database 中死锁计数器的变化
代码层面预防：确保事务中的SQL操作顺序一致
实时监控：使用系统视图查询作为辅助诊断工具

预防胜于治疗！通过合理的应用设计和数据库配置，可以大大减少死锁的发生频率。

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