Function check_request_columns 

fn check_request_columns<C: RequestColumn>(
    region_id: RegionId,
    metadata: &RegionMetadata,
    columns: HashMap<&str, C>,
    check_missing: impl FnMut(&ColumnMetadata) -> Result<()>,
) -> Result<bool>

Checks the columns of a write request against the region schema. Each column must be a column of the region, have its data type and, if the request carries one, its semantic type, and contain nulls only if the region column is nullable. check_missing checks the region columns that the request doesn’t have. Returns whether there are such columns.