// dataUsageHash is the hash type used.
type dataUsageHash string

// sizeHistogramV1 is size histogram V1, which has fewer intervals esp. between
// 1024B and 1MiB.
type sizeHistogramV1 [dataUsageBucketLenV1]uint64

// sizeHistogram is a size histogram.
type sizeHistogram [dataUsageBucketLen]uint64

// versionsHistogram is a histogram of number of versions in an object.
type versionsHistogram [dataUsageVersionLen]uint64