Function fresh_segment_count 

pub fn fresh_segment_count(
    plan: &DataQualityPlan,
    may_read_blocks: bool,
) -> SegmentCount

Where a run of plan that reads a new sample gets its segment totals. may_read_blocks is whether the sample may be seeded runs of one file, which see too few rows to count; the head sees too few as well. Every other sample is one streamed pass over the scope, which counts the grain’s key as it goes.