graph/api/graph.go中的代码怎么理解

[reymont]

`nowTs := time.Now().Unix()
lastUpTs := nowTs - nowTs%int64(step)
rra1StartTs := lastUpTs - int64(rrdtool.RRA1PointCnt*step)

// consolidated, do not merge
if start_ts < rra1StartTs {
	resp.Values = datas
	goto _RETURN_OK
}`

rra1StartTs 代表什么意思？怎样理解这段代码？