if ROS master is running in another machine, does it get all topics stream?

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If ROS master is running in another machine, does it get all topics stream?

No, it doesn't.

But that is also the case for a single-machine setup: the master is not involved in topic or service data exchange at all, so it never receives or sends any of that data. No matter where it is running.

As explained on wiki/Master, it only provides naming and registration services. All data exchange between nodes is peer-to-peer and does not pass through the master.

I wonder if the stream of all topics are sent to the rosmaster machine or only to the ones is subscribed to?

Nodes running on different machines will only send data to other machines if those nodes have subscribed to those topics.

If you have a 100 machines, each with a single node, but no subscriptions between them, no data will be transmitted.