Hello, our team is interested in exploring realtime upsert tables, but I am curious about the maintenance and scaling of the table going forward. Conceptually I understand that the same partition of data has to always route through the same server for this to work. Referencing these docs: https://docs.pinot.apache.org/manage-data/data-import/upsert-and-dedup/upsert#enable-upserts-in-pinot I see we must use

{
  "routing": {
    "instanceSelectorType": "strictReplicaGroup"
  }
}

and also

numInstancesPerPartition=1

With this is mind, is it still possible to scale up the number of servers horizontally once the table is set up? And what is the process then to do so?

You can safely scale the number of servers. The only caveat is scaling number of partitions. So you want to slightly over provision partition count in upstream

Okay thanks that's good to know