1. Does the transaction replication have any load on the primary server(pardon my use of generic terms) when its moving data out.
Many factors that it depends --
- On the activity on the primary server which will be the Publisher server. Also, if the distribution agent on the same or different server matters a lot as it will be doing the heavy work of delivering the transactions of the articles that are published by the publisher server.
On the geographic location of the Publisher - subscriber servers due to the limitation of the connectivity between the 2 regions (if geographically distributed).
On how many articles and the the amount of data you are publishing. Remember if for some reasons, the articles subscription expires, then you have to reinitialize the subscribers by a snapshot and the amount of data will affect it. Only replicate what you need. Dont replicate the entire database.
I have seen subscribers lagging data by hours even in same region and same data center due to massive amount of transactions generated by Publisher.
To be concise, there will be latency on the subscriber server and depending on the amount of activity on the publisher server along with whether Distribution database is on the same or different server, there will be some or heavy activity on the publisher (primary -- not accurate term for replication) server.
2. If the subscriber server goes down, will the primary still function
Yes, if the subscriber goes down, there will be no impact on Primary, EXCEPT the replication jobs will be failing and depending on the expiration policy you have setup, you might end up re-initializing the subscribers with a snapshot.