What is the difference between Seeking and Snapshot in Pub/Sub Subscription?
Seeking and Snapshots aren’t directly comparable – one is (sometimes) used as part of the other 🙂
Seeking is basically a way to alter the state of acknowledgement of messages in bulk. For example, you can seek to a timestamp in the past, and all messages received after that time will be marked as unacknowledged. Seeking can also be used to purge a queue, by seeking to a time in the future.
Snapshots are used in seeking as an alternative to a timestamp. You need to create a snapshot at a point in time, and that snapshot will retain all messages that were unacknowledged at the point of the snapshot’s creation, as well as any messages published to the topic thereafter. Unlike timestamps, you don’t need to configure any special topic configuration to use snapshots (like retain_acked_messages). Snapshots are particularly useful when rolling out application updates, so if you roll back a change you can also "roll-back" your topic to a snapshot.
For more info see: https://cloud.google.com/pubsub/docs/replay-overview
Hope this helps!