Setting affected by the sync activity level include:
work_mem: The sync query result set sizes may be large for subscriptions that haven't been synced for a while. Also, the subscriptions need to be sorted. By default, the client will sync every 5 minutes so the number of sync changes is not likely to be very large, but clients that are offline will build up large outstanding sync result sets. Setwork_memhigher if clients are expected to be offline for long periods of time.