keyviz: support to merge cold logical range

Signed-off-by: Zheng Xiangsheng <hundundm@gmail.com>

pkg/keyvisual/matrix/axis.go

@@ -236,6 +236,61 @@ func (c *chunk) Focus(strategy Strategy, threshold uint64, ratio int, target int
 	}
 	generateBucket(len(c.Values))
 
+	newChunk := createChunk(newKeys, newValues)
+	if len(newValues) >= target*2 {
+		newChunk = newChunk.MergeColdLogicalRange(strategy, threshold, target)
+	}
+	return newChunk
+}
+
+func (c *chunk) MergeColdLogicalRange(strategy Strategy, threshold uint64, target int) chunk {
+	threshold /= 4 // TODO: This var can be adjusted
+
+	newKeys := make([]string, 0, target)
+	newValues := make([]uint64, 0, target)
+	newKeys = append(newKeys, c.Keys[0])
+
+	coldStart := 0
+	coldEnd := 0
+	var coldRangeSum uint64 = 0
+	mergeColdRange := func() {
+		if coldEnd <= coldStart {
+			return
+		}
+		newKeys = append(newKeys, c.Keys[coldEnd])
+		newValues = append(newValues, coldRangeSum)
+		coldStart = coldEnd
+		coldRangeSum = 0
+	}
+	generateRange := func(end int) {
+		if end <= coldEnd {
+			return
+		}
+		var rangeSum uint64 = 0
+		for i := coldEnd; i < end; i++ {
+			rangeSum += c.Values[i]
+		}
+		if coldRangeSum > threshold || rangeSum > threshold {
+			mergeColdRange()
+		}
+		if rangeSum > threshold {
+			newKeys = append(newKeys, c.Keys[coldEnd+1:end+1]...)
+			newValues = append(newValues, c.Values[coldEnd:end]...)
+			coldStart = end
+		} else {
+			coldRangeSum += rangeSum
+		}
+		coldEnd = end
+	}
+
+	for i := range c.Values {
+		if strategy.CrossBorder(c.Keys[i], c.Keys[i+1]) {
+			generateRange(i + 1)
+		}
+	}
+	generateRange(len(c.Values))
+	mergeColdRange()
+
 	return createChunk(newKeys, newValues)
 }