可靠发布的发件箱模式
学习事务发件箱模式，以原子方式提交业务状态和待发送消息，消除事件驱动系统中的双写问题。
可靠发布的发件箱模式 是 CoddyKit 上的免费 RabbitMQ Messaging & Async Systems 课时。 这是第 4 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 RabbitMQ Messaging & Async Systems 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 RabbitMQ Messaging & Async Systems 课程共包含 4 节课。
本课时的部分内容尚未翻译，以英文显示。
The Dual-Write Problem
Saving to a database and publishing to RabbitMQ are two separate operations. If one succeeds and the other fails, your state and your events drift apart.
This is the dual-write problem.
What Is the Outbox Pattern?
The outbox pattern writes the business change and the outgoing message into the same database transaction, then publishes the message asynchronously from the outbox table.
The Outbox Table
Create a table that stores pending messages alongside your domain data.
CREATE TABLE outbox (
id UUID PRIMARY KEY,
payload JSONB,
published BOOLEAN DEFAULT FALSE,
created_at TIMESTAMPTZ DEFAULT now()
);Atomic Write
In one transaction, update the business row and insert the outbox row. Either both commit or neither does.
BEGIN;
INSERT INTO orders (id, status) VALUES ('42', 'paid');
INSERT INTO outbox (id, payload) VALUES (gen_random_uuid(), '{"order":"42"}');
COMMIT;The Relay Process
A separate relay (or message dispatcher) polls the outbox for unpublished rows, publishes them to RabbitMQ, and marks them published.
Polling the Outbox
The relay selects pending rows in order and publishes each one.
SELECT id, payload FROM outbox WHERE published = FALSE ORDER BY created_at;At-Least-Once Delivery
If the relay crashes after publishing but before marking the row, it republishes on restart. So consumers must be idempotent to tolerate duplicates.
Change Data Capture Alternative
Instead of polling, tools like Debezium tail the database write-ahead log and stream outbox inserts to RabbitMQ, reducing latency and load.
Combining With Confirms
The relay should use publisher confirms so it only marks a row published after the broker acknowledges the message, closing the loss window.
Outbox vs Saga
The outbox guarantees a single service reliably emits its events. A saga coordinates a multi-service workflow. They complement each other: each saga step can publish via its own outbox.
Cleanup and Retention
- Periodically delete or archive published rows
- Index on
publishedfor fast polling - Monitor relay lag to catch stalls early
Quick Check
Test your outbox understanding.
Recap
The outbox pattern stores outgoing messages in the same transaction as business data, then a relay publishes them to RabbitMQ asynchronously.
It eliminates the dual-write problem, requires idempotent consumers due to at-least-once delivery, and pairs well with publisher confirms and sagas.
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常见问题解答
「可靠发布的发件箱模式」课时是免费的吗？
是的 — 「可靠发布的发件箱模式」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 RabbitMQ Messaging & Async Systems 课程的其余内容，请升级到 CoddyKit PRO。 RabbitMQ Messaging & Async Systems 课程共包含 4 节课。
「可靠发布的发件箱模式」这节课中我会学到什么？
学习事务发件箱模式，以原子方式提交业务状态和待发送消息，消除事件驱动系统中的双写问题。 你通过在浏览器中直接运行的动手代码来练习 RabbitMQ Messaging & Async Systems，全天候 AI 导师会在你学习这节课的过程中回答你的问题。
学习 RabbitMQ Messaging & Async Systems 需要有经验吗？
无需任何先前经验。CoddyKit 上的 RabbitMQ Messaging & Async Systems 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 4 节课，共 4 节。
「可靠发布的发件箱模式」课时需要多长时间？
大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。
我能在这节 RabbitMQ Messaging & Async Systems 课中编写并运行代码吗？
能。每节 RabbitMQ Messaging & Async Systems 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。