为什么 Vercel 部署后 PostgreSQL 仍然存在 Idle 连接

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为什么 Vercel 部署后 PostgreSQL 仍然存在 Idle 连接



如果你在 Vercel 上运行 Next.js， 并且直接连接 PostgreSQL，你很可能遇到过下面的错误： 

remaining connection slots are reserved for roles with the SUPERUSER attribute

这个问题通常在重新部署后更容易出现，即使你的应用流量并不高。

常见现象

  • PostgreSQL 中存在大量 idle 状态的连接
  • Vercel 实例已经关闭，但连接仍未释放
  • 新请求无法获取数据库连接
  • 手动终止连接只能暂时缓解问题

真正的原因

这是 Serverless 架构的正常行为。

Vercel 的工作方式大致如下：

  1. Vercel 根据请求启动多个 Serverless 实例
  2. 每个实例都会创建自己的数据库连接或连接池
  3. 实例结束后，无法保证数据库连接被优雅关闭
  4. PostgreSQL 会继续保留这些连接直到超时

结果就是：应用已经结束，但数据库连接仍然存在。

为什么会导致连接数耗尽

在托管 PostgreSQL 服务中，一部分连接被保留给系统和 SUPERUSER。

当 Serverless 实例频繁创建连接时，很容易用完普通用户可用的连接数， 从而触发该错误。

这不是数据库 bug，而是架构不匹配导致的问题。

PgBouncer 如何解决

PgBouncer 位于应用和数据库之间： 

Vercel → PgBouncer → PostgreSQL
  • 应用连接 PgBouncer，而不是直接连接数据库
  • PgBouncer 使用少量真实数据库连接服务大量请求
  • Serverless 实例关闭时，连接会被立即回收
  • PostgreSQL 不再堆积 idle 连接

对于 Serverless 场景，推荐使用 transaction pooling 模式。

推荐配置

  • 启用 PgBouncer
  • 应用连接 PgBouncer 的 host 和 port
  • Node.js 连接池设置为 1–2
  • idleTimeoutMillis 设置为 5 秒左右
  • 设置 idle_in_transaction_session_timeout

总结

这个问题看起来像是 Vercel 的问题，但实际上是 Serverless + 直连数据库 的经典陷阱。

如果你在 Vercel 上使用 PostgreSQL， PgBouncer 是必需的，而不是可选的。

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