Function description_lookahead 

fn description_lookahead(
    lookahead: Duration,
    timestamp_interval: Duration,
) -> Option<u64>

How far past the remap upper the minter commits its ceiling while a snapshot pins the frontier, in milliseconds, the unit of mz_repr::Timestamp. None turns committing ahead off.

timestamp_interval is the floor to avoid having data outrun the ceiling. Remap emits a new binding and downgrades its capability together. Rows emitted by reclock under the new binding are racing the new ceiling to the batch writers. At one timestamp interval the previous ceiling already covers the current timestamp’s rows. Rows still outrun it when consecutive probes are further apart than the lookahead, which costs a batch rather than correctness.