# Synchronous SUBSCRIBE Handling

CybusMQ processes SUBSCRIBE requests synchronously across the cluster. The broker only sends the SUBACK response when all nodes are ready to route messages to the subscribing client.

## How It Works

When a client sends a SUBSCRIBE request, CybusMQ performs the following steps before sending SUBACK:

1. Replicates the subscription data to all cluster nodes.
2. Updates routing tables on all nodes.

This synchronous approach ensures that when a client receives SUBACK, the cluster is ready to deliver messages immediately.

## Message Loss Prevention

During overload scenarios, asynchronous subscription processing can cause the first few messages to be lost after SUBACK is sent. CybusMQ's synchronous approach prevents this by ensuring all cluster nodes are ready before confirming the subscription.


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.cybus.io/broker/cybusmq/configuration/synchronous-subscribe-handling.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.