Constant IMPORT_ROUND_SIZE 

const IMPORT_ROUND_SIZE: u64 = _; // 67_108_864u64

While a bulk import goes on (set_importing), full rounds wait until this device appended this much since the last one: the import’s records go out once, in the rounds that continue the last full one, and a single full round follows the import, not one every few megabytes of it.