Waits for every queued data-key row to land, so a writer of sealed values
stores nothing before the keys it was sealed under. Every flusher of sealed
rows calls it first.
Returns Promise<any[]>
a promise, resolved when they have (whatever their outcome)
Waits for every queued data-key row to land, so a writer of sealed values stores nothing before the keys it was sealed under. Every flusher of sealed rows calls it first.