Hi n_u,

When we say ephemeral we mean that if the host compute dies in a permanent way (which happens from time to time) the data on the NVMe drives attached to that host is not recoverable by us. AWS/GCP might have recovery mechanisms internally it, but we don't have API access to those APIs.

When we say "semi-synchronous replication" we mean it in the sense of MySQL semi-synchronous replication: https://dev.mysql.com/doc/refman/8.4/en/replication-semisync.... To be honest I'm not exactly sure where the "semi" comes from but here are two possible reasons I can think of why:

1. We actually only require that 1 of the 2 replicas sends an acknowledgement to the primary that it has durably stored the transaction to its relay log before the primary in turn sends an acknowledgement back to the client application. 2. The transaction is visible (can be read) on both the primary and the replica _before_ the primary sends back an acknowledgement that the transaction was committed back to the client application.

Thanks! I see. It's maybe a term they came up with to place it between async and fully synchronous replication.